Thermo doi: 10.3390/thermo6020034

Authors: Assadour Khanjian Ibrahim S. Resen Ali Al Shaer Youssef Ezzeddine Mahdi Awada Ahmed Mohsin Alsayah Jalal Faraj Mahmoud Khaled

Creating secondary flows that encourage fluid interchange between hot and cold regions is frequently necessary to improve convective heat transfer in compact channels. A well-known passive method for enhancing mixing and boosting thermal performance in laminar regimes is the use of vortex generators (VGs), which create streamwise and transverse vortices. Laminar forced convection in a rectangular channel with rectangular wing vortex generators with triangular tips is investigated numerically in this work. The primary goal is to assess the impact of the number of tips per wing on pressure drop and heat transfer enhancement at a fixed angle of attack (α). This study examines a single row of rectangular wing vortex generators (VGs) with triangular tips and systematically evaluates how variations in tip number influence not only the global Nusselt number and friction factor but also the three-dimensional vortex structure distribution along the channel. This approach contrasts with many previous studies that primarily focus on global performance indices or on classical delta-type VGs. ANSYS Fluent’s finite volume method is used to solve three-dimensional stable, laminar, incompressible flow and heat transfer. Two Reynolds numbers, Re = 456 and Re = 911, are simulated for different triangular-tip configurations at a fixed angle of attack of α = 30°. To connect flow structures to heat transfer behavior, area-averaged Nusselt numbers and friction factors are calculated for each case, and vortex cores and their spatial locations are examined. The findings demonstrate that heat transfer improvement is directly and significantly impacted by the VG tip arrangement. The trade-off between heat gains and pressure losses is highlighted by the fact that some tip configurations produce stronger, more persistent vortices and higher Nusselt numbers at the expense of an increased friction factor. The conclusions are limited to laminar flow conditions at α = 30°, Reynolds numbers of 456 and 911, and the investigated one-, two-, and three-tip configurations.

Thermo doi: 10.3390/thermo6020033

Authors: Yangfan Zhong Zhijie Gong Taocheng Zhao Chengcheng Fan Chaoqun Shen

As the heat flux of electronic devices continues to increase, conventional air cooling and single-phase liquid cooling technologies are increasingly constrained by heat transfer limits and pumping power consumption. However, systematic investigations on the coupling between microchannel evaporators and the overall dynamic response of MPTL systems remain limited. To address this issue, a visualization experimental platform for the microchannel MPTL was developed, and flow boiling experiments were conducted under varying heat fluxes and circulating flow rates. Key parameters including wall temperature, fluid temperature, pressure drop, and flow patterns were measured to characterize the thermal–hydraulic behavior of the system. The results show that the wall temperature increases stepwise with increasing heat flux, reaching a critical heat flux of 814.2 W/cm2 at a mass flux of 105.6 kg/(m2·s), where heat transfer deterioration occurs. During this transition, inlet temperature oscillations with an average amplitude of 8 °C were observed due to vapor backflow. With decreasing circulating flow rate, the flow pattern evolved sequentially from single-phase flow to bubbly, slug, churn, annular, and reverse annular flow, accompanied by a shift in the dominant heat transfer mechanism from forced convection to nucleate boiling and convective evaporation. The best heat transfer performance occurred under annular flow conditions at an outlet vapor quality of 0.4–0.5. These findings provide useful guidance for the design and operation optimization of microchannel MPTL systems in high-heat-flux electronic cooling applications.

Thermo doi: 10.3390/thermo6020032

Authors: Yujie Yuan Chun Sing Lai Loi Lei Lai Zhuoli Zhao

This paper offers a critical review of cutting-edge research on multi-energy microgrids (MEMs), with a novel exploration of their potential role in supporting urban air mobility (UAM), specifically electric vertical takeoff and landing (eVTOL) aircraft. While extensive research has focused on improving the economic performance and emission reductions of MEMs, particularly in the context of electric vehicle (EV) charging, there remains a significant gap in understanding how microgrids can support the decarbonization of UAM. The paper examines the opportunities and challenges of integrating microgrids with UAM operations, highlighting the need for more research to optimize energy management systems that balance renewable energy use with the growing demand for aerial transport. Thermal energy storage systems are emphasized as a critical component for addressing transportation energy needs, offering a promising solution to reduce carbon emissions while enhancing system efficiency. This review aims to provide new insights into how the coupling of microgrids and UAM can contribute to the development of economically and environmentally sustainable smart cities.

Thermo doi: 10.3390/thermo6020031

Authors: Ana Ivette Delgado-Moreno Raúl Ricardo Quiñonez-López María de Jesús Palacios-Sánchez Oscar Guillermo Zúñiga-González Francisco Javier Moscoso-Sánchez Eulogio Orozco-Guareño Jesús Baudelio Campos-García

The thermochemical properties of Norharmane, Harmane, and Harmine were investigated using DSC, combustion calorimetry, thermogravimetry, and G3B3 computational methods. DSC measurements enabled accurate determination of melting temperatures and fusion enthalpies. Complementary IR, NMR, and HPLC analyses performed for Harmine indicate that partial degradation occurs during the melting process, becoming more evident at higher temperatures (above ~330 °C). The standard enthalpies of formation in the solid state were 159.6 kJ·mol−1 (Norharmane), 80.5 kJ·mol−1 (Harmane), and −47.0 kJ·mol−1 (Harmine). Using sublimation enthalpies derived from TGA, the gas-phase formation enthalpies were established as 282.7, 186.0, and 87.4 kJ·mol−1, respectively. Homodesmotic G3B3 calculations showed excellent agreement with experimental data, with absolute deviations below 1.5 kJ·mol−1. The combined results reveal a consistent thermodynamic stability trend in both phases: Harmine > Harmane > Norharmane.

Thermo doi: 10.3390/thermo6020030

Authors: Mihaela Constantin Antonios Detzortzis Cătălina Dobre

This study presents a combined numerical and experimental investigation of transient multiphase compressible flow inside a profiled-rotor rotary volumetric compressor. While most existing studies rely on high-fidelity CFD approaches, a low-order thermodynamic chamber-based model implemented in MATLAB Release 2023a is proposed to predict the temporal evolution of pressure, temperature, and vapor volume fraction during the compression cycle. The model is based on mass and energy conservation applied to variable-volume control chambers and incorporates a simplified cavitation criterion derived from local pressure relative to saturation vapor pressure. An open-loop experimental test bench was developed to measure air mass flow rate, suction and discharge pressures, temperatures, torque, and shaft power under controlled operating conditions. These measurements are used to validate the numerical predictions. The results show good agreement between measured and simulated pressure levels and global performance indicators, with deviations quantified using mean absolute percentage error values remaining below 5% over the investigated operating range. The numerical analysis further reveals the occurrence of localized low-pressure zones during the suction phase, indicating incipient cavitation or microbubble formation at specific rotor positions. The proposed modeling approach provides a computationally efficient alternative to full CFD simulations and enables rapid parametric analysis of rotor geometry and operating conditions. The cavitation formulation does not aim to resolve detailed bubble dynamics or erosion mechanisms, but rather to identify cavitation tendency based on thermodynamic pressure thresholds.

Thermo doi: 10.3390/thermo6020029

Authors: Sharif Md. Yousuf Bhuiyan Md. Kamrul Hasan Rajib Mahamud

Electrohydrodynamic effects can significantly alter transport processes in reacting flows, even when the plasma is weakly ionized. However, predictive modeling of such plasma–flame interactions remains challenging due to the multiscale coupling among charge transport, fluid motion, and chemical kinetics. This study presents a charge-transport closure model to investigate electrohydrodynamic influences on laminar non-premixed flames. A two-dimensional computational framework in cylindrical coordinates is used to simulate plasma-assisted methane–air diffusion flames under weak electric-field conditions representative of practical combustion environments. To represent plasma–flow coupling in a computationally feasible yet physically consistent manner, a charge-transport formulation based on the drift–diffusion approximation is employed. The model solves transport equations for representative positive and negative charge carriers coupled with Poisson’s equation for the electric potential to obtain a self-consistent electric field. This formulation assumes a weakly ionized regime for low-temperature plasma-assisted combustion, in which neutral species dominate the mass and momentum transport, while ionization chemistry is simplified and charge transport primarily influences the flow through electrohydrodynamic body forces and Joule heating. Assuming a weak electric field, the steady flamelet model is applied, in which plasma effects primarily influence scalar transport and local thermal balance rather than inducing significant bulk ionization dynamics. The governing equations are discretized using a high-order compact finite-difference scheme that provides improved resolution of steep gradients in temperature, species concentration, and space-charge density near thin reaction zones. The canonical laminar flame model configuration was validated using the established laminar methane–air diffusion flame benchmark, and steady-state spatial profiles of key transport properties were evaluated. Two-dimensional analysis identified the discharge coupling location as an important factor. The application of discharge in the fuel-air mixing region leads to a clear restructuring of the flame. When the discharge is activated, electrohydrodynamic forcing and ion-driven momentum transfer produce a highly localized, columnar flame with sharp gradients and a confined reaction zone. Compared with the baseline case, the plasma-assisted flame localizes the OH-rich reaction zone, confines the high-temperature region into a narrow column, and enhances downstream H₂O formation.

Thermo doi: 10.3390/thermo6020028

Authors: Qi He Chunyu Qu Wenjie Zuo

AI data-center (DC) growth is increasingly constrained by limited deliverable electricity, interconnection capacity, and cooling demand. This study develops a boundary-consistent screening framework for waste-to-energy (WtE)-coupled AI DC cooling, treating cooling as an energy service that can be supplied through grade matching rather than solely through electricity-driven mechanical chilling. The framework translates plant-side exportable heat into corridor-level planning objects by explicitly accounting for thermal attenuation, absorption-based conversion, and parasitic electricity associated with delivery and auxiliaries. Three results structure the analysis. First, a reference-case energy-service ledger shows how a representative regulated WtE plant with municipal solid-waste throughput of 1500 t/day and lower heating value of 10 MJ/kg yields ~78.1 MWth of exportable driving heat and, at a 20 km corridor, ~53.0 MWcool of delivered cooling and ~8.0 MWe of net avoided cooling electricity after parasitic debiting. Second, the coupled system is governed by operating regimes, not a single efficiency score. Under the baseline package, full thermal coverage is maintained up to ~20.9 km, the stricter quality-adjusted criterion remains positive to ~22.9 km, and the electricity–relief criterion remains positive to ~44.7 km. Third, deployment-scale translation for a 1 GW IT campus (u=0.70, L=5 km) implies a net grid relief of ~116.9–264.4 MW across scenario packages, while the required WtE footprint ranges from roughly three to 148 equivalent representative plants, or about 0.6–40 full-load-equivalent plants at a 25% displacement target. The contribution is a siting-ready planning framework that identifies when WtE-coupled cooling remains corridor-feasible, when it becomes hybrid and marginal, and when infrastructure scale rather than thermodynamic benefit becomes the binding constraint. It is intended as a screening tool for planning and comparison, not as a project-specific hydraulic or plant-cycle design.

Thermo doi: 10.3390/thermo6020027

Authors: Laurențiu Mihail Constantin Lavinia Grosu Tiberiu Catalina Adalia Andreea Percembli (Chelmuș) Daniel Taban Claudia Ioniță Alexandru Dobrovicescu

This study investigates steady-state conductive heat transfer and water-vapor diffusion through the external wall of a refrigerated warehouse with a specified load-bearing wall assembly. The formal analogy between heat conduction and mass diffusion is stated and used to establish a practical calculation framework for estimating heat and moisture ingress through multilayer cold-store walls. Calculation routines are presented to determine the temperature field and the corresponding water-vapor saturation and partial-pressure distributions across (and within) the insulation layer, enabling the identification of regions prone to interstitial condensation. The analysis highlights the roles of (i) the vapor diffusion resistance of the vapor barrier layer, (ii) the thermal resistance of the insulation, and (iii) key outdoor boundary conditions in governing condensation risk. Increasing insulation thermal resistance reduces external heat gains; however, it may also increase the likelihood of condensation in layers close to the cold side by lowering local temperatures and saturation pressures. Among external parameters, outdoor relative humidity exerts the strongest influence on interstitial condensation risk. For the investigated wall assembly, increasing outdoor relative humidity by 50% shifts the condensation onset location within the insulation toward mid-thickness. The effects of vapor barrier diffusion resistance, insulation thermal resistance, and changes in outdoor conditions (relative humidity, temperature, and wind speed) are reported in tabulated form and illustrated through pressure–position and temperature–position profiles.

Thermo doi: 10.3390/thermo6020026

Authors: Yitbarek Firew Minale Ivan Gajdoš Tamas Szabo Annamaria Polyákné Kovács Andrea Ádámné Major Kálmán Marossy Grzegorz Janowski

Polyvinyl chloride (PVC) is widely used in engineering applications; however, its inherent thermal instability associated with dehydrochlorination limits its processing window and long-term performance. While blending with thermoplastic polyurethane (TPU) and plasticization are common strategies to improve flexibility, their combined influence on the thermal behavior and stability of PVC, particularly when bio-based plasticizers are employed, has not been thoroughly investigated. In this study, the thermal behavior and stability of PVC/TPU blends plasticized with glycerol diacetate monolaurate, a bio-based plasticizer derived from waste cooking oil, were investigated. Dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy (FTIR) were used to examine segmental mobility and intermolecular interactions, while scanning electron microscopy (SEM) provided insight into microstructural organization. Thermal stability was evaluated through conductivity-based dehydrochlorination measurements, complemented by thermogravimetric and derivative thermogravimetric analyses (TGA/DTG) to assess degradation behavior. The results showed that neither TPU nor the bio-plasticizer alone improved the resistance of PVC to dehydrochlorination. In contrast, ternary PVC/TPU/bio-plasticizer blends exhibited a pronounced delay in HCl evolution, accompanied by a more homogeneous phase distribution and interaction-driven modification of the molecular environment. TGA/DTG analysis indicated that this stabilization arises from altered degradation kinetics rather than a simple shift in degradation onset. Overall, the findings clarify the thermal behavior of PVC-based blends and demonstrate a sustainable formulation approach for achieving flexible and thermally balanced PVC materials while reducing reliance on potentially toxic phthalate plasticizers.

Thermo doi: 10.3390/thermo6020025

Authors: Cuitlahuac Iriarte-Cornejo Resty L. Durán Victor M. Maytorena Jesús F. Hinojosa Sául F. Moreno

Heating gases to high temperatures is essential for supplying energy to thermal and thermochemical processes. This study presents the optical–thermal design of a mini heliostat field coupled with a tubular solar receiver equipped with second optics, aiming to heat nitrogen to approximately 850 K. The secondary optical system redistributed up to 40% of the incident solar flux from the front to the rear surface of the receiver, improving radial temperature uniformity and significantly reducing thermal gradients along the tube wall. An overall optical efficiency of 65.25% was achieved, accounting for atmospheric attenuation, shading, blocking, and the cosine effect. A coupled computational model was developed by solving the conservation equations of mass, momentum, and energy, with the spatially resolved solar flux distribution obtained via ray tracing used as a thermal boundary condition. The simulation results, validated with an empirical correlation, include solar flux contours, nitrogen temperature distributions, surface temperatures, and heat transfer coefficients. The configuration with a 12 mm vertex spacing between secondary reflectors demonstrated the best thermal performance, reducing the maximum tube surface temperature by 11% and improving radial symmetry, while maintaining nitrogen outlet temperatures near the design target of 850 K. These results confirm the suitability of the system for high-temperature applications such as solar pyrolysis using nitrogen as the heat transfer fluid to deliver the required thermal energy.

Thermo doi: 10.3390/thermo6020024

Authors: Hassan Abdulmouti Muhammed Elmnefi Muhanad Hajjawi Nawwal Ismael Ibrahim Zakwan Skaf Mazhar Azeem

This study experimentally investigates the dynamics of air bubble plumes in water under varying thermal and hydrodynamic conditions using a two-dimensional Particle Image Velocimetry (PIV) system. The experimental setup consists of a transparent acrylic tank equipped with a bubble generator, a controlled heating system, and a synchronized PIV arrangement to capture both bubble motion and the induced liquid flow field. Experiments were conducted over a range of water temperatures (21–60 °C), air flow rates, and water depths (200–600 mm) to systematically quantify their coupled influence on bubble plume behavior. The results demonstrate that bubble rising velocity (defined here as the mean vertical, buoyancy-driven component of bubble motion measured in the fully developed plume region) increases with water temperature, gas flow rate, and water depth. For a fixed gas flow rate and water depth, increasing the water temperature from 40 °C to 60 °C resulted in an approximately twofold increase in bubble rising velocity, primarily due to reduced liquid viscosity and enhanced buoyancy forces. Bubble velocity also increased with gas flow rate and water depth, reflecting stronger momentum input and extended acceleration distances within taller water columns. PIV-resolved velocity fields further reveal that the surrounding fluid velocity increases proportionally with bubble rising velocity and temperature, confirming a strong coupling between bubble motion and plume-induced circulation. The surrounding liquid velocity reached approximately 30–60% of the corresponding bubble rising velocity, depending on operating conditions. These findings provide quantitative experimental insight into the coupled effects of thermal conditions, gas injection rate, and liquid depth on bubble–liquid interactions. The results contribute valuable validation data for multiphase flow modeling and offer practical relevance for thermal–hydraulic, chemical, and environmental engineering applications involving bubble-driven transport processes.

Thermo doi: 10.3390/thermo6020023

Authors: Mónika Ferencz Barna Nagy János Gyenis Tivadar Feczkó

This study investigates how an internal PCM–gypsum plaster lining modifies orientation-dependent heat transfer through lightweight model house envelopes over a full spring season. Two identical container houses (reference and PCM plastered) were monitored for 105 days under free-floating conditions, and surface temperatures of all opaque elements were processed into characteristic temperature differences and corresponding heat flux densities at daily extrema. The analysis showed that wall and roof orientation strongly governed both the magnitude and variability of these characteristic heat fluxes. West-facing façades and the roof exhibited the highest values due to solar gains and radiative exchanges, while the floor and north wall remained comparatively stable. Under conditions of nearly constant mean wall temperature, the characteristic flux framework revealed that the PCM lining systematically reshaped the temporal distribution of heat transfer and reduced the effective net energy exchange between indoor space and outdoor environment, most notably on solar-exposed west and south walls and on the roof. These orientation-resolved heat flux indicators provided a physically transparent basis for deciding on which envelope surfaces PCM integration could be most advantageous and where its application could be omitted without significantly compromising thermal performance under similar climatic conditions.

Thermo doi: 10.3390/thermo6010022

Authors: Martín Salazar-Pereyra Ladislao Eduardo Méndez-Cruz Wenceslao Bonilla-Blancas Raúl Lugo-Leyte Sergio Castro-Hernández Helen D. Lugo-Méndez

Cogeneration system optimization in refineries confronts the challenge of simultaneously integrating design parameter selection and topological configuration. The literature typically addresses these aspects separately: parametric optimization with fixed topology or configuration optimization for specific nominal conditions. This work develops a comprehensive methodology integrating exhaustive parametric exploration with superstructure-based optimization through mixed-integer nonlinear programming (MINLP), applied to the Miguel Hidalgo refinery in Tula, Mexico. The systematic procedure generates superstructures considering all viable expansion and tempering routes under steam quality restrictions (x≥0.88), evaluating 84–105 combinations of generation pressure (PHRSG=70–140 bar) and superheater outlet temperature (Ts4=500–560 °C). The analysis reveals three topologically distinct configurations identified as generating maximum power under different operating conditions and characterizes how transitions between high-performing configurations occur at discrete thermodynamic thresholds that correlate with constraint activation contradicting the conventional assumption of continuous parameter-configuration relationships. Multi-criteria evaluation positions Configuration 1 as the recommended design, generating 25% increase in electric generation, 11% improvement in utilization factor (UF: 0.640→0.710) and 20% reduction in specific fuel consumption (SFC: 0.259→0.207 kg/kWh). The methodology is directly generalizable to other refineries through universal thermodynamic principles, with a systematic five-step procedure applicable to any multi-pressure steam demand profile. The characterization of discrete transition phenomena and the associated methodology for their thermodynamic explanation challenges the conventional assumption of continuous parameter–configuration relationships in optimization approaches, with immediate implications for the design of flexible cogeneration systems in refineries worldwide.

Thermo doi: 10.3390/thermo6010021

Authors: Márcio Santos André Sousa Jorge André Ricardo Mendes José B. Ribeiro

Carnot batteries based on the coupling of high-temperature heat pumps (HTHPs) and Organic Rankine Cycles (ORCs) emerge as promising solutions for large-scale and long-duration energy storage, enabling sector coupling and the valorization of industrial waste heat. In such systems, the charging subsystem plays a dominant role, as variations in heat pump performance influence the round-trip efficiency more strongly than comparable variations in the ORC. This work presents a thermodynamic assessment of Rankine-based HP–ORC Carnot batteries focusing on the influence of heat pump configuration and working fluid selection. System performance is evaluated using the heat pump coefficient of performance, volumetric heat capacity, ORC efficiency, and Carnot battery round-trip efficiency through a grid-search optimization over a wide range of storage outlet and waste heat source temperatures. The results show that single-stage configurations are optimal at low to moderate temperature lifts, while two-stage and cascade systems become advantageous at higher lifts. Among the investigated fluids, R-601 provides the highest round-trip efficiencies at elevated storage temperatures, whereas R-600 enables more compact systems due to its higher volumetric heat capacity. These findings provide design guidance for selecting heat pump configurations and working fluids in industrial waste-heat-assisted Carnot battery applications.

Thermo doi: 10.3390/thermo6010020

Authors: Ivan Ignatkin Nikolay Shevkun Dmitry Skorokhodov

Ensuring the required microclimate parameters is the most critical task in hot climates. In pig farms, air cooling is provided by means of steam-compression chillers or evaporative cooling, which is the simplest way to cool the air. The implementation of evaporative cooling depends largely on the interaction of the media involved in this process. This paper considers the process of interaction of cooling water with the surface of a cellular polycarbonate heat exchanger. A mathematical model describing the process of wetting the sprayed surface of the heat exchanger is obtained. The authors determined the theoretical water flow rate required to provide air cooling for a given operation mode. Experimental trials of a recuperative heat recovery unit with a heat exchanger made of cellular polycarbonate equipped with a water evaporative cooling system were carried out. The authors conducted a comparative assessment to evaluate the effectiveness of evaporative cooling in a heat recovery unit equipped with a polycarbonate heat exchanger versus panel evaporative systems using wetted paper pads at pig farms in the Vladimir and Tambov regions of Russia. The panel evaporative coolers provided a temperature reduction of 11.3 °C without any splashing effect. Under the same operating conditions, the heat recovery unit achieved an inlet air temperature reduction of 10.5 °C, accompanied by splashing. When the water flow rate supplied for evaporation was reduced until the splashing ceased, the cooling temperature drop decreased to 10.1 °C, which is 11% lower, compared with the paper pads. The study revealed characteristic operating modes for the unit that ensure effective air cooling, depending on the cooling water flow rate. Since the prevailing temperature during the system’s main operating time is significantly lower than the design temperature (the absolute temperature maximum), to achieve effective cooling of the supply air without splashing or excessive water waste, the cooling circuit water should circulate at a flow rate within 40 to 63% of the maximum design value. Alternatively, an automated control system should be employed to regulate the water supply based on outdoor air temperature and humidity.

Thermo doi: 10.3390/thermo6010019

Authors: Aubrey Jaffer

Based on Jaffer’s (2023) heat engine analysis of natural convection, this investigation mathematically derives a novel, comprehensive formula predicting the natural convective heat transfer from an inclined cylinder given its length, diameter, angle, and Rayleigh number and the fluid’s Prandtl number and thermal conductivity. The present formula was tested with 93 inclined cylinder measurements having length-to-diameter ratios between 1.48 and 104 in nine data-sets from three peer-reviewed studies, yielding (data-set) root-mean-squared relative error values between 1.9% and 4.7%.

Thermo doi: 10.3390/thermo6010018

Authors: Ashraf Emad Almerane Aizat Abas

While twisted tape inserts are widely used for heat transfer enhancement, the specific impact of tape thickness remains under-explored. This study provides a systematic numerical investigation into the thermo-hydraulic performance of a double-pipe heat exchanger equipped with twisted perforated tape (TPT) inserts of varying thicknesses (1, 1.5, and 2 mm). Using a validated 3D SST k−ω model across Re = 1000–12,000, the research establishes a mechanistic distinction between flow regimes. The results indicate that the 2 mm TPT yields the highest enhancement, achieving a 78.6% increase in the average Nusselt number (Nuavg) and a 67.8% improvement in the overall heat transfer coefficient at Re = 12,000. Quantitative analysis of secondary flow intensity and turbulence kinetic energy confirms a transition from geometry-induced swirl at low Re to turbulence-driven shear at high Re. Despite a pressure drop penalty of up to 3.26 times the plain tube, the thermal performance factor remained above unity for all cases, peaking at 1.17 at Re ≈ 4000. These findings establish tape thickness as a first-order design variable for optimizing high-performance thermal systems.

Thermo doi: 10.3390/thermo6010017

Authors: José-María Martínez-Val Ignacio López-Paniagua

Thermodynamic cycles used with external combustion are typically based on compression, heating, expansion and cooling, admitting variants to enhance efficiency or power. This paper carries out a thorough theoretical study of isochoric heating and non-adiabatic expansion processes and proposes a new thermodynamic cycle based on three instead of four stages. The compressor is removed because the working fluid (a gas) is pressurized by heating it isochorically. A novel concept of an engine is proposed (patent ES2992009A, WO 2025/257447), and it shows potential for power generation that has to be explored.

Thermo doi: 10.3390/thermo6010016

Authors: Aiym Kereikulova Yelnar Yerdesh Yerzhan Belyayev Amankeldy Toleukhanov Olivier Botella Abdelhamid Kheiri Mohammed Khalij

Thermal stratification strongly affects the efficiency and operational reliability of sensible thermal energy storage (TES) tanks in energy systems. This study numerically investigates the combined influence of inlet configuration and mass flow rate on the charging performance of a vertical cylindrical TES tank (H = 3 m, D = 1 m) using transient CFD simulations. Five inlet designs—open, orifice, groove, shower, and shower-groove are analyzed at three flow rates: Q1 = 0.0003 m3/s, Q2=Q1/2, and Q3=Q1/3. System performance is evaluated using key thermal and stratification metrics. Increasing the flow rate from Q3 to Q1 enhances convective heat transfer and energy and exergy efficiencies, but significantly intensifies mixing and degrades thermal stratification. At Q1, the groove inlet achieves the highest capacity ratio and exergy efficiency (0.87), while exhibiting increased mixing. Reducing the flow rate to Q2 and Q3 limits inlet-induced momentum, leading to improved stratification for all configurations. The shower-groove inlet reaches a maximum stratification level (tail factor) of 1.13 at Q3, indicating superior thermal layering, albeit with lower energetic efficiency (≈0.40–0.45). The groove inlet provides the best overall compromise at Q2, combining high efficiency with stable stratification. These results demonstrate a clear efficiency-stratification trade-off and highlight the importance of selecting inlet-flow combinations according to application-specific objectives.

Thermo doi: 10.3390/thermo6010015

Authors: Masoud Sahami Hojat Ghassemi Angel Terziev Kostadin Fikiin Borislav Stankov George Pitchurov Martin Ivanov

The rapid evaporation of liquid droplets across a normal shock wave is a phenomenon of critical importance in advanced propulsion and clean energy systems, such as NH3 supersonic separation. The conventional Spalding d2-law is commonly used to model such phenomena, but it is not suitable for predicting the complete vaporization of sub-micron droplets, particularly as evaporation approaches the free-molecular regime. To address this issue, this paper introduces a novel time-dependent one-dimensional CFD model, which is used to analyze the shock structure, the non-equilibrium heat and mass transfer between the liquid and gas phases, and the evolution of the droplets’ size through the shock. The model describes the evaporation of NH3 sub-micron droplet sprays across a stationary normal shock for various fractions of the liquid phase. The Gyarmathy evaporation model is utilized to accurately account for the transition from diffusion-governed to free-molecular regimes, alongside a new two-phase Rankine–Hugoniot shock jump formulation. The study reveals the influence of a steady normal shock on the physical structure of a droplet-laden flow, including the existence of an initial droplet size swelling through the shock, and quantifies the subsequent complete evaporation of the suspended droplets. The maximum swelling throughout the shock is up to 17%, which corresponds to the case with 8% liquid phase mass fraction in the flow. The model provides acceptable accuracy in calculating the two-phase parameters in high-speed flows and can be extended for modeling more complex, multidimensional detonation and propulsion systems.

Thermo doi: 10.3390/thermo6010014

Authors: Sharif H. Zein

Thermochemical conversion of plastic waste to hydrogen and synthesis gas represents a potential pathway for energy recovery from heterogeneous waste streams. The feasibility and performance of such systems are fundamentally governed by thermodynamic constraints and heat-management requirements. This review critically examines the thermodynamic and heat-integration aspects of plastic waste conversion to hydrogen and syngas, with emphasis on pyrolysis, steam reforming, gasification, and system-level behaviour. Key thermodynamic features of plastic pyrolysis, reforming, and gasification are discussed, including reaction endothermicity, equilibrium limitations, temperature effects, and product distribution trends. The role of steam reforming and water–gas shift reactions in enhancing hydrogen yield is assessed from equilibrium and energy-demand perspectives. Heat integration emerges as a critical determinant of overall efficiency, with recoverable waste heat present at multiple process stages offering opportunities for internal heat recovery. Energy and exergy analyses identify dominant sources of irreversibility and enable comparison of plastic-derived hydrogen systems with conventional thermochemical hydrogen production routes. Quantitatively, conventional steam methane reforming achieves energy efficiencies of 65–75% and exergy efficiencies of 60–70%, whilst plastic-derived systems without extensive heat integration report 45–60% and 40–55%, respectively. Key challenges include limited thermodynamic property data for real plastic-derived mixtures, insufficient reconciliation of equilibrium and kinetic behaviour, incomplete system-level heat-integration analysis, and scarcity of comprehensive exergy-based evaluations. This review provides a thermodynamic framework for assessing the opportunities and limitations of hydrogen production from plastic waste.

Thermo doi: 10.3390/thermo6010013

Authors: Fabio Iozzino Andrea Fragnito Gerardo Mauro Carlo Roselli

The integration of Foamed Concrete (FC) into 3D Concrete Printing (3DCP) processes facilitates the design of energy-efficient building envelopes. However, strategies for optimizing material porosity and printing topology to balance winter and summer performance remain underexplored. This study presents a 2D numerical thermal analysis of an innovative 3D-printed building envelope block characterized by sinusoidal internal partitions. Through a parametric variation in porosity (ranging from 10% to 50%) and internal geometry (amplitude and period of the partitions), 45 distinct configurations were simulated. Performance was evaluated by calculating the steady-state thermal transmittance (U) and the periodic thermal transmittance (Yie) under dynamic climatic conditions. The results demonstrate that porosity is the governing parameter; increasing porosity from 10% to 50% reduces U by 31% and, contrary to traditional assumptions for massive structures, also improves Yie by 12.3%. These outcomes are physically driven by the drastic reduction in thermal conductivity, which overcompensates for the loss of thermal mass, leading to a net reduction in overall thermal diffusivity. While internal topology plays a secondary role, its optimization allows for fine-tuning dynamic damping without compromising insulation. The study confirms that 3D printing with foamed concrete enables the overcoming of the traditional trade-off between insulation and thermal inertia. High-porosity configurations (50%) with optimized internal topology emerge as the most effective solution, simultaneously guaranteeing beneficial steady-state and dynamic thermal performance for sustainable buildings.

Thermo doi: 10.3390/thermo6010012

Authors: Huibo Zhang Jinwu Xiang Dawei Bie Daochun Li Zi Kan Lintao Shao Zhi Geng

In the original publication [...]

Thermo doi: 10.3390/thermo6010011

Authors: Abdulwahed Mushabbab Abdulelah Alhamayani Andrew Chiasson

Photovoltaic–thermal (PVT) collectors often experience limited heat extraction under laminar cooling conditions, and the influence of controlled flow pulsation on full-scale PVT performance has not been clearly established. This study experimentally investigates a water-cooled PVT system operated under pulsating flow using an indoor solar simulator to quantify its thermal and electrical response. Flow pulsations were generated using a solenoid valve at frequencies of 0.25, 0.5, 1, and 2 Hz across inlet flow rates of 1–4 L/min, with average irradiance maintained between 700 and 800 W/m2. System performance was benchmarked against uncooled and continuous-flow reference cases. Pulsating operation reduced the PVT surface temperature and produced a clear enhancement in thermal performance relative to continuous flow, while electrical efficiency exhibited a smaller but consistent improvement that followed the same thermal trend. A pulsation frequency of 0.5 Hz yielded the most favorable results, achieving thermal efficiencies exceeding 50% at higher flow rates without any measurable increase in average pressure drop. Electrical efficiency stabilized at approximately 9.82%, slightly higher than that obtained under continuous-flow operation. The results indicate that low-frequency pulsating flow can significantly improve thermal energy extraction in PVT systems under controlled conditions, with modest associated electrical gains, and provide a basis for further investigation of flow-modulation strategies for thermally driven PVT applications.

Thermo doi: 10.3390/thermo6010010

Authors: Manuel G. Satué Alfredo P. Vega-Leal Juana M. Martínez-Heredia Manuel R. Arahal

Recently, different techniques have been proposed for the scheduling and loading problems in cooling plants with chillers in a parallel configuration. Two broad groups can be considered: the online control-based group and the offline optimization-based group. The first group is exemplified by Model Predictive Control, where the selection of control moves provides a solution to both scheduling and loading. The second group includes Optimal Chiller Loading and Optimal Chiller Sequencing algorithms. They usually derive operating plans with some lead time in a batch-like fashion for long horizons. Both groups use forecasts of important factors such as the cooling demand and ambient conditions; hence, they have to deal with inaccuracies in the forecasts. In this paper, a comparison among these two groups is made considering demand uncertainties. The severity of the uncertainty is shown to play a role in the results as well as the controller tuning in the case of the predictive approach. The results are favorable to OCS with respect to overall consumption (up to 15%) but uses more on/off changes in the chiller’s operation (double in some cases).

Thermo doi: 10.3390/thermo6010009

Authors: Stanislava Ivanova Charles F. Croft Tsveta Sarafska James N. Smith Lea Kukoc Spas D. Kolev Tony G. Spassov

The development of deep eutectic solvents (DESs) is a key issue for the realization of green and efficient metal extraction processes. The present study aims to experimentally construct the phase diagram of the binary system consisting of tri-n-octylphosphine oxide (TOPO) and 4,4,4-trifluoro-1-phenyl-1,3-butanedione (HBTA) and, thus, determine its eutectic composition for the solvent extraction of Li+. Differential scanning calorimetry was used to characterize the phase transitions (melting temperatures and enthalpies) over the entire composition range of the binary mixture. Its eutectic composition was established at HBTA:TOPO mass ratio of 60:40. For further validation of the eutectic composition from the experimentally measured thermal effects for melting of different HBTA:TOPO mass ratios, a Tammann diagram was also constructed. Only mixtures with HBTA:TOPO mass ratios of 70:30, 60:40 (eutectic composition), and 50:50 were liquids at 30 °C, while at room temperature of 25 °C, the 70:30 mixture formed crystals. All three mixtures, which were liquids at 30 °C, were found to extract Li+ effectively. However, at a room temperature of 25 °C, only the eutectic mixture (60:40 mass ratio) extracted Li+ effectively, while the mixture with HBTA:TOPO mass ratio of 50:50 formed crystals when mechanically agitated and, therefore, was deemed as unsuitable for Li+ extraction.

Thermo doi: 10.3390/thermo6010008

Authors: Edwin N. Hernandez-Estrada José B. Robles-Ocampo Perla Y. Sevilla-Camacho Marco Antonio Zúñiga Reyes Roberto Adrian González Domínguez Juvenal Rodriguez-Resendiz

A firewood stove’s combustion chamber can withstand temperatures of 1500 °C. To prevent the deterioration of a firewood stove due to excessive heat, it is necessary to use thermal insulation materials that stop heat transfer to the walls. These materials must be economical and durable. This work examines the materials used in the construction of combustion chambers of firewood stoves in southern Mexico and Central America. This field study collects information and samples of materials used in the manufacture of firewood stoves. Heat transfer experiments are conducted, and the thermal properties of each material are analyzed. As a result, methodology and information is provided for the manufacture of future plancha-type firewood stoves used in the study area, such as pine wood (pinus chiapensis) which is mainly used as casing for firewood stoves in coniferous forest areas; in addition, the use of wood ash as thermal insulation material is proposed since it does not present direct costs and has a thermal conductivity between 0.10 and 0.20 W/m°C and a melting point greater than 1500 °C. The next layer proposed is hollow brick, a high-temperature-resistant material that can be used as support due to its mechanical strength and low thermal conductivity of 0.6 W/m°C. Finally, the use of calcium hydroxide as a coating material is proposed, applied in the form of a paste or paint to detail the imperfections of the combustion chamber construction as it resists temperatures above 1000 °C.

Thermo doi: 10.3390/thermo6010007

Authors: Alevtina Gosteva Alexander M. Kalinkin Vladimir Vinogradov Diana Manukovskaya Viktor Nikolaev Vasilii Semushin Maria Teplonogova

Double complex salts (DCSs) of the composition [Co(NH3)6][Fe(CN)6] are a promising precursor for the preparation of catalysts for the hydrogenation of carbon oxides (CO and CO2) by Fischer–Tropsch synthesis. The specific surface area is an important parameter for catalysts. Our article investigates the influence of mechanochemical activation (MCA) on this DCS in order to determine the conditions for obtaining the largest specific surface area of the intermetallic compound, a product of the DCS thermolysis. In this work, the effect of MCA on the physicochemical properties of the DCS [Co(NH3)6][Fe(CN)6] and the products of its thermal decomposition in an argon atmosphere were investigated. It was shown that MCA leads to partial reduction of Fe+3 to Fe+2, changes in the coordination of ammonia, amorphization of the structure and a decrease in the thermal stability of DCS. Thermolysis at 650 °C of samples subjected to MCA for 10 min results in the formation of nanocrystalline intermetallic compound Co0.5Fe0.5. The results demonstrate the potential of using MCA to control the properties of functional materials based on DCS.

Thermo doi: 10.3390/thermo6010006

Authors: Rogério Pazetto Saldanha da Gama Rogério Martins Saldanha da Gama Maria Laura Martins-Costa

This work presents a straightforward procedure for constructing the solution to the steady-state energy-transfer process in a system of two convex, opaque, gray bodies, with the aim of determining the temperature distribution within these bodies when separated by a vacuum. The methodology proposed in this work combines a sequence of elements that are functions obtained from the solution of uncomplicated, well-known linear, uncoupled heat transfer problems, thereby enabling solutions to be obtained using tools found in basic engineering textbooks. Specifically, these well-known problems resemble classical conduction-convection heat transfer problems, in which the boundary condition is described by the noteworthy Newton’s law of cooling. The limit of sequences of elements that are solutions to straightforward linear problems corresponds to the original, complex, coupled nonlinear problem. The convergence of these sequences is mathematically proven. The phenomenon (considered in this work) encompasses those involving black bodies. Since each element of the sequence arises from a well-known linear problem, numerical approximations can be used to obtain it, yielding a simple and powerful tool for simulations. Some presented results highlight the importance of considering thermal interaction between the two bodies, even in the absence of physical contact. In particular, the alterations in the temperature distributions of two separate gray bodies are explicitly shown to result from their thermal interaction.

Thermo doi: 10.3390/thermo6010005

Authors: Laszlo Garbai Robert Santa Mladen Bošnjaković

To balance the quantity of heat generated and consumed, thermal energy storage systems are crucial for power plants and district heating systems. Particularly when phase transitions and pressure variations are not adequately covered in the existing literature, their work frequently takes place under complicated, changing temperature and fluid dynamic settings. The goal of this research is to create a thermodynamic model that incorporates the effects of steam condensation, steam injection, and heating failures to describe the transient behaviour of temperature and pressure in pressure vessels containing single-phase and two-phase fluids. To account for nonlinear, temperature-dependent steam properties, as well as initial and boundary constraints, the study proposes energy balance models for hot water and saturated steam cases. Numerical simulations evaluating sensitivity to parameter changes are presented alongside analytical solutions for isochoric and isobaric systems. The model also includes direct steam injection heating and the use of a heat exchanger. It explains the changes in temperature and pressure that occur in thermal energy storage systems over time, including significant events such as steam cushion collapse and condensate drainage. According to the sensitivity analysis, the main factors influencing the system’s safety limitations and transient dynamic phenomena are thermal power, heat exchanger capacity, and thermal insulation efficiency. The proposed thermodynamic model closes a major gap in the literature by providing reliable predictions of the transient behavior needed for the safe design and reliable operation of pressure vessels utilized for heat storage in district heating networks. This model can be used by engineers and researchers to optimize system design and steer clear of risky operational situations.

Thermo doi: 10.3390/thermo6010004

Authors: Perla Yadav Lakith Jinadasa Alex Wray Simon Petrovich Marios Georgiou Kambiz Ebrahimi

Improving the architecture and control strategies of thermal management systems (TMSs) is crucial for minimizing energy consumption in heating and cooling components, thereby enhancing the driving range of Battery Electric Vehicles (BEVs). This study presents a holistic approach for developing an Integrated Thermal Management System (ITMS) based on an Octo-valve-type architecture, designed to efficiently manage the thermal demands of both the cabin and powertrain components. Empirical data were collected under various heating and cooling scenarios across a wide operating temperature range (−20 °C to 40 °C), and these data were used to parametrize and validate key ITMS components. Experimental results demonstrated that the parametrized simulation model closely replicated the cabin and battery thermal behavior observed in vehicle tests, particularly under cooling conditions. Minor deviations, such as cabin temperature overshoot during heating scenarios, were attributed to duct thermal effects and control tuning limitations. Overall, the optimized Octo-valve-based ITMS architecture exhibited thermal trends consistent with literature references and effectively validated the proposed control strategy, demonstrating improved thermal efficiency and potential range enhancement for BEVs across diverse environmental conditions. Furthermore, ITMS energy consumption over the indicated temperature range is quantified in this research paper.

Thermo doi: 10.3390/thermo6010003

Authors: Wichean Singmai Pichet Janpla Suparat Jamsawang Kittiwoot Sutthivirode Tongchana Thongtip

This work proposes the design, construction, and field test of a vacuum seawater desalination system (VSDS) driven by an evacuated tube solar collector (with a total absorption area of 1.86 m2) under tropical climatic condition (Thailand ambient at latitude 13°43′06.0″ N, longitude 100°32′25.4″ E). The VSDS prototype was designed and constructed to be driven by hot water, which is produced by two heat source conditions: (1) an electric heater for laboratory tests and (2) an evacuated tube solar collector for field tests under real climatic conditions. A comparative experimental study to assess the ability to produce fresh water between a conventional dripping/pipe feed column and spray falling film column is proposed in the first part of the discussion. This is to demonstrate the advantage of the spray falling film distillation column. The experimental method is implemented based on the batch system, in which the cycle time (distillation time) considered is 10–20 min so that heat loss via the concentrated seawater blow down is minimized. Later, the field test with solar irradiance under real climatic conditions is demonstrated to assess the freshwater yield and the system performance. The aim is to provide evidence of the proposed vacuum desalination system in real operation. It is found experimentally that the VSDS working with spray falling film provides better performance than the dripping/pipe feed column under the specified working conditions. The spray falling film column can increase the distillated freshwater volume from 1.33 to 2.16 L under identical cycle time and working conditions. The improvement potential is up to 62.4%. The overall thermal efficiency can be increased from 33.7 to 70.8% (improvement of 110.1%). Therefore, the VSDS working with spray falling film is selected for implementing field tests based on real solar irradiance powered by an evacuated tube solar collector. The ability to produce fresh water is assessed, and the overall performance via the average distillation rate and the thermal efficiency (or Gain Output Ratio) is discussed with the real solar irradiance. It is found from the field test with solar time (8.00–16.00) that the VSDS can produce a daily freshwater yield of up to 4.5 L with a thermal efficiency of up to 19%. The freshwater production meets the requirement for international standard drinking water criteria, indicating suitability for household/community use in tropical regions. This work demonstrates the feasibility of VSDS working under real solar irradiance as an alternative technology for sustainable fresh water.

Thermo doi: 10.3390/thermo6010002

Authors: Anarbay Kudaykulov Azat Tashev Bagdat Teltayev Aizhan Muta

In this study, the thermomechanical behavior of a variable cross-section rod with fixed ends is studied using an analytical method. A rod with a radius that varies quadratically with length is considered, and it is thermally insulated on its side surface. Heat flow is applied to the left end of the rod, and heat exchange with the environment occurs at the right end. Based on the obtained temperature distribution, the thermal strains, stresses, displacements, and total elongation are determined. The results highlight the influence of boundary thermal conditions on the thermomechanical response of the rod, which is of interest for the design and analysis of structural elements operating under conditions of uneven thermal stress.

Thermo doi: 10.3390/thermo6010001

Authors: Aurang Zaib Abdur Rehman Mazhar Cheng Zeng Tariq Talha Hasan Aftab Saeed

The low thermal conductivity of phase-change materials (PCMs) remains a key limitation in latent heat thermal energy storage systems, leading to slow melting and incomplete energy recovery. To address this challenge, this study explores extended Y-Fin geometries as a novel heat transfer enhancement strategy within a concentric-tube latent heat thermal energy storage configuration. Six fin designs, derived from a baseline Y-shaped structure, were numerically compared to assess their influence on the melting and solidification behavior of stearic acid. A two-dimensional transient enthalpy–porosity model was developed and rigorously verified through grid, temporal, and residual convergence analyses. The results indicate that fin geometry plays a critical role in enhancing heat transfer within the PCM domain. The extended Y-Fin configuration achieved the fastest melting time, 28% shorter than the baseline Y-Fin case, due to improved thermal penetration and bottom-region accessibility. Additionally, the thermal performance was evaluated using nano-enhanced PCMs (10% Al2O3 and CuO in stearic acid) and paraffin wax. The addition of Al2O3 nanoparticles significantly improved thermal conductivity, while paraffin wax exhibited the shortest melting duration due to its lower melting point and latent heat. This study introduces an innovative fin architecture combining extended conduction paths and improved convective reach for efficient latent heat storage systems.

Thermo doi: 10.3390/thermo5040059

Authors: Brent Mellows Yolanda Sanchez-Vicente

Biofuels represent a viable alternative to fossil fuels due to their lower greenhouse gas emissions, potential for large-scale production, and renewable nature. Orange oil, turpentine, and their hydrogenated derivatives have emerged as promising candidates for biofuel components. Efficient design and operation of internal combustion engines require knowledge of biofuel density and viscosity as functions of temperature; however, experimental data on these properties remain limited. In this work, the densities and viscosities of turpentine, orange oil, hydrogenated turpentine, and hydrogenated orange oil were measured at atmospheric pressure over the temperature range (293.15–373.15) K. The measurements were performed with uncertainties below 0.05 kg·m−3 for density and 0.3 mPa·s for viscosity. The experimental data were correlated as a function of temperature using a quadratic function for density and the Andrade equation for viscosity, with absolute average relative deviations of 0.01% for density and 0.5% for viscosity. For all substances, both viscosity and density decrease with increasing temperature, and they are lower than the values for biodiesel. Orange oil and turpentine exhibited higher densities but lower viscosities than their hydrogenated counterparts, which can be attributed to differences in molecular size and packing efficiency. Finally, the measured density and viscosity values are compared with the limit values specified in the European and American biodiesel standards. The analysis shows that blending these essential oils with conventional biodiesel could result in biofuel mixtures that meet both standards.

Thermo doi: 10.3390/thermo5040058

Authors: Diana Marel Ruiz-Ruiz Luis Jesús Ramírez-Ramírez Aarón Almaraz-Gómez Ayrton Homero Bautista-Aguilar José Guadalupe Chacón-Nava Gabriel Plascencia

To satisfy the needs of an ever-growing population, it is imperative to cope with the extended demand for copper. To do so, copper makers mostly rely on pyrometallurgical processes that are characterized by emitting hazardous gases and solid wastes, and by the fact that these processes are energy demanding. Additionally, copper makers face the issue of processing leaner ore bodies or exploiting mineral deposits already overexploited or about to end their productivity cycle. These problems compromise the sustainable production of copper. Because of that, this study focuses on the leading technology in use to assess and identify possible solutions in order to improve the efficiency of energy usage and to decrease the amount of wastes generated in copper pyrometallurgy. To do so, reliable thermodynamic databases and Sankey diagrams were used to determine possible improvements. For example, it is determined that by increasing the mass ratio of Fe/Cu in the mineral feedstock may result in increasing the copper content in the matte, and thus reducing the exergy flows, resulting in improved energy usage. Another positive impact is that using oxygen-enriched air with higher copper concentrations could decrease SO2 emissions by nearly 25%. Among other detrimental environmental issues, they entail.

Thermo doi: 10.3390/thermo5040057

Authors: Mateo Kirinčić Tin Fadiga Boris Delač

This study investigates the thermal performance of a passive vertical aluminum heat sink with plate fins through combined experimental measurements and numerical simulations. Using a custom-made experimental apparatus which used water as the heat source, heat transfer rate was determined, and heat transfer coefficient was compared against established empirical correlations, demonstrating good agreement. A 3D steady-state mathematical model was developed to capture the conjugate heat transfer problem of conduction and natural convection, with buoyancy-driven airflow modeled with the incompressible ideal gas law. The problem was solved numerically using the finite volume method through ANSYS Fluent 18.2 solver and validated against experimental data and analytical correlations, exhibiting good agreement throughout. Parametric analysis followed, investigating the influence of various base (50, 65, 80 °C) and ambient (19, 24, 29 °C) temperatures, resulting in base-to-ambient temperature differences from 21 to 61 °C. Increasing this temperature difference led to a significant increase in heat transfer rate, while heat transfer coefficient increased and overall thermal resistance decreased moderately. Additionally, a Nusselt–Rayleigh (Nu–Ra) number correlation, consistent with ranges reported in the literature, was derived, providing the scaling to predict the thermal performance of similar natural convection-governed heat sinks. The validated computational methodology, combined with obtained experimental and numerical results, presents a foundation for future studies focused on more complex heat sink geometries and physics.

Thermo doi: 10.3390/thermo5040056

Authors: Thouraya Ghnimi Lamine Hassini Mohamed Bagane

This paper presents a new study and analysis of the thermo-hygroscopic behavior of Arthrospira platensis using dynamic vapor sorption (DVS) system. Thermo-hygroscopic characterization is essential for optimizing the drying process and enhancing storage conditions. Therefore, the objective of this work was to investigate the thermo-hygroscopic properties of Arthrospira (Spirulina) platensis using a dynamic vapor sorption (DVS) system. This thermo-hygroscopic analysis focused on three fundamental parameters, namely: the desorption isotherms, the net isosteric heat of water desorption, and the moisture diffusivity. Desorption isotherms were measured at five different temperatures (25 °C, 40 °C, 50 °C, 60 °C and 80 °C) over a relative humidity range of 10–80%. The desorption isotherm data were fitted to five semi-empirical models: GAB, Oswin, Smith, Henderson, and Peleg. The results indicated that the GAB model provided the best fit for the experimental data. The net isosteric heat of desorption was determined using the Clausius–Clapeyron relation. It decreased from 21.3 to 4.29 KJ/mol as the equilibrium moisture content increased from 0.02 to 0.1 Kg/Kg (dry basis). Additionally, the moisture diffusivity of Arthrospira platensis was estimated based on Fick’s second law of diffusion and the desorption kinetics obtained from the DVS equipment. This parameter varied between 1.04 10−8 m2/s and 1.46 10−7 m2/s for average moisture contents ranging from 0.003 Kg/Kg to 0.191 Kg/Kg (dry basis). Furthermore, the activation energy for desorption was estimated to be approximately 33.7 KJ/mol.

Thermo doi: 10.3390/thermo5040055

Authors: Thorstein Wang Zhiliang Zhang Jianying He

As devices and systems shrink in size, understanding heat transfer at the mesoscopic scale becomes increasingly critical for the design of efficient thermal management strategies. This study investigates convective heat transfer in concentric cylinders, a geometry which is relevant to small-scale technologies. Finite elements simulation are used to examine the influence of geometry and temperature on effective thermal conductivity, and on a parameter introduced as the apparent heat transfer coefficient. It is found that the effective thermal conductivity goes above unity for inner and outer radii at the millimeter scale, which is smaller than that predicted by the available analytical studies. This deviation is attributed to the fact that finite element simulations capture the behavior of temperature boundary layers more accurately at small scales than these analytical models. These insights aid in identifying conditions in which convection can be ignored, significantly simplifying thermal simulations. This work also reveals that at the mesoscale, the ratio between outer and inner radius for which a cylinder can be considered free-standing is much larger than at the macroscale. This highlights the importance of taking the surrounding surfaces into consideration when performing experiments on the heat transfer properties of mesoscale cylinders such as wires.

Thermo doi: 10.3390/thermo5040054

Authors: Beyza Bozali Sepideh Ghodrat Kaspar M. B. Jansen

Knitted heaters have attracted significant interest due to their flexibility and ease of integration into smart textile applications. However, uneven heat distribution remains a major challenge, leading to comfort issues and inefficient energy usage. This study presents an analytical, physics-based model that links the resistance, power distribution, and surface temperature of knitted heaters to key design parameters such as size, configuration, material properties, and knitting structure to establish guidelines for achieving a desired temperature rise over a specified surface area. The model was validated experimentally across a range of heaters (3–12 lines) arranged in ladder and diagonal configurations. Results showed good agreement between predictions and measurements for higher line counts (10–12), while larger deviations occurred in smaller heaters (3–5 lines) due to contact resistance and current losses. A prototype knitted wristband demonstrated physiologically relevant heating (>33 °C) under safe, low-voltage operation. These findings provide a quantitative design framework for optimizing knitted heaters and highlight their potential for scalable integration into wearable and therapeutic applications.

Thermo doi: 10.3390/thermo5040053

Authors: Niloufar Ziasistani Andrés Meana-Fernández Antonio José Gutiérrez-Trashorras

The building sector accounts for nearly 40% of global energy consumption and over one-third of energy-related carbon emissions. Therefore, it is vital to adopt low-carbon design strategies. Double-Skin Façades (DSFs) offer significant potential to improve energy efficiency through the dynamic control of heat and daylight. This study evaluates the combined effects of building orientation, fixed shading devices, and adjustable blinds on the performance of DSFs across six cities representing diverse climate types: Phoenix, Stockholm, Kuala Lumpur, London, Cape Town, and Tokyo. Using a model developed in DesignBuilder, 852 scenarios were simulated with 5-min time steps over a full year. The results show that optimal orientation depends on the climate and that cooling load may be reduced up to 59%, with CO2 emission savings up to 11.7% compared to a base south-facing configuration. External blinds outperformed internal blinds in reducing the cooling demand, reaching reductions of up to 27.7% in hot climates, though often increasing the heating load in cold climates. Combining overhangs and external blinds provided additional cooling savings in some cases but was generally less effective than external blinds alone. The findings highlight the importance of climate-specific DSF designs, with orientation and external blinds being the most effective strategies for reducing operational energy use and emissions.

Thermo doi: 10.3390/thermo5040052

Authors: Lorenz Hammerschmidt Zlatko Raonic Michael Tielsch

Air cycle systems, once largely replaced by vapour-compression technologies due to efficiency concerns, are now re-emerging as a viable and sustainable alternative for highly dynamic thermal applications and excel in ultra-low temperature. By using air as the working fluid, these systems eliminate the need for synthetic refrigerants and comply naturally with evolving environmental regulations. This study presents the conceptual design and simulation-based analysis of a novel air cycle machine developed for advanced automotive testing environments. The system is intended to replicate a wide range of climatic conditions—from deep winter to peak summer—through the use of fast-responding turbomachinery and a flexible control strategy. A central focus is placed on the radial turbine, which is designed and evaluated using a modular, open source framework that integrates geometry generation, off-design CFD simulation, and performance mapping. The study outlines a potential operating strategy based on these simulations and discusses a control architecture combining lookup tables with zone-specific PID tuning. While the results are theoretical, they demonstrate the feasibility and flexibility of the proposed approach, particularly the turbine’s role within the system.

Thermo doi: 10.3390/thermo5040051

Authors: Claudio Giorgi Angelo Morro

This paper is devoted to the modelling of nonlocality in continuum physics through constitutive functions that depend on suitable gradients. For definiteness, the attention is addressed to elastic solids, heat conductors, and magnetic solids. Models are developed where both the requirements of the second law of thermodynamics and the balance equations are satisfied for the constitutive functions that involve gradients of strain, temperature, heat flux, and magnetization. Concerning elastic and magnetic solids, it is shown that, depending on the chosen variables, the standard symmetry property of the stress holds identically. The models so developed are free from any hyperstress tensor frequently considered in the literature.

Thermo doi: 10.3390/thermo5040050

Authors: Alevtina Gosteva Semen Lapuk Alexander Gerasimov

Complex compounds are under close scrutiny by scientists as precursors, which are needed to produce functional materials. When the thermolysis method of double complex salts is used on an industrial scale, the most detailed information on the thermal decomposition, including the kinetics of decomposition, is required. The kinetics of pyrolysis, solid, and gaseous products of [Co(NH3)6][Fe(C2O4)3]∙2H2O (I) and [Co(en)3][Fe(C2O4)3] (II) (en—ethylenediamine) thermolysis were studied in this work. The solid products of thermal decomposition were studied using scanning electron microscopy and elemental analysis, and the specific surface area (8 and 71 m2/g, respectively) was measured. It was determined that a double complex salt (DCS) with a coordinated en has a higher thermal stability than with NH3 due to the chelation effect.

Thermo doi: 10.3390/thermo5040049

Authors: Ngoc-Thien Tran Van-Thuc Nguyen Thanh Trung Do Van-Sung Nguyen

Heat input always plays a crucial role in enhancing penetration depth within the heat-affected zone (HAZ) of the orbital TIG welding process. The heat tint, in addition, caused by heat input, is a decisive factor for the quality of sanitary tube welds, which AWS D18.2 strictly regulates. Therefore, controlling heat input to achieve complete penetration while maintaining an acceptable heat tint level is considered essential in sanitary tube welding. For this reason, this study conducted 27 experimental welds with variations in the parameters of the Orbital TIG Welding process to determine the optimal welding parameters for sanitary tubes with an outer diameter of Ø38.1 mm and a thickness of 1.65 mm. Taguchi analysis identified the optimal parameter combination to achieve full penetration as a welding current of 100 A, an arc length of 1.5 mm, and a welding speed of 5 mm/s. In addition, the use of internal backing gas and arc time significantly improved the heat tint level of the welds produced under the proposed parameter set.

Thermo doi: 10.3390/thermo5040048

Authors: Srinivasan Venkatraman Chandrasekaran Selvam

The present study aims to experimentally investigate pool boiling heat transfer characteristics, such as critical heat flux (CHF) and boiling heat transfer coefficient (BHTC), of pure distilled water (d-H2O) and functionalised graphene nanoplatelet (f-GnPs)–d-H2O nanofluids using a nichrome (Ni-Cr) test wire as the heating element. The distilled water (dH2O) and GnP (5–10 nm and 15 µm, Cheap Tubes, USA) were chosen as the base fluid and nanomaterial, respectively. The GnP was chemically functionalized and dispersed in dH2O using a probe sonicator. The nanofluids were characterized by measuring the zeta potential distribution and pH to ensure stability on day 1 and day 10 following preparation. The results show that the zeta potential values range from −31.6 mV to −30.6 mV, while the pH values range from 7.076 to 7.021 on day 1 and day 10, respectively. The novelty of the present study lies in the use of f-GnPs with a controlled size and stable nanofluid, confirmed through zeta potential and pH analysis, to determine the heat transfer behaviour of a Ni-Cr test wire under pool boiling conditions. The pool boiling heat transfer characteristics, such as CHF and BHTC, were observed using the fabricated pool boiling heat transfer test facility. Initially, the dH2O and f-GnP–dH2O nanofluids were separately placed in a glass container and heated using a pre-heater to reach their saturation point of 100 °C. The electrical energy was gradually increased until it reached the critical point of the Ni-Cr test wire, i.e., the burnout point, at which it became reddish-yellow hot. The CHF and BHTC were predicted from the experimental outputs of voltage and current. The results showed an enhancement of ~15% in the CHF at 0.1 vol% of f-GnPs. The present study offers a method for enhancing two-phase flow characteristics for heat pipe applications.

Thermo doi: 10.3390/thermo5040047

Authors: Caimiao Zheng Jianli Hao Shiwang Yu Luigi Di Sarno Yuan Shi Ji Han

Coal-to-Synthetic Natural Gas (SNG) plays a crucial role in China’s decarbonization strategy but faces significant sustainability challenges due to its carbon-intensive nature. This study integrates Life Cycle Assessment (LCA) with Box–Behnken Design and Response Surface Methodology (BBD-RSM) to quantify and optimize key parameters for emission reduction. The LCA results indicate that 90.48% of total emissions originate from the SNG production stage, while coal mining accounts for 9.38%, leading to a carbon intensity of 660.92 g CO2eq/kWh, second only to conventional coal power. Through BBD-RSM optimization, the optimal parameter combination was identified as a raw coal selection rate of 62.5%, an effective calorific value of 16.75 MJ/kg, and a conversion efficiency of 83%, corresponding to an energy-based rate of return (ERR) of 49.79%. The optimized scenario demonstrates a substantial reduction in total life-cycle emissions compared with the baseline, thereby improving the environmental viability of coal-to-SNG technology. Furthermore, this study employs the energy-based rate of return (ERR) as a normalization and comparative evaluation metric to quantitatively assess emission reduction potential. The ERR, combined with BBD-RSM, enables a more systematic exploration of emission-driving factors and enhances the application of statistical optimization methods in the coal-to-SNG sector. The findings provide practical strategies for promoting the low-carbon transformation of the coal-to-SNG industry and contribute to the broader advancement of sustainable energy development.

Thermo doi: 10.3390/thermo5040046

Authors: Mariana Luna Lourenço Pedro Akira Bazaglia Kuroda Carlos Roberto Grandini

When it comes to developing new titanium alloys for biomaterials, β metastable alloys have been gaining the most attention from researchers, as they have a lower elastic modulus and the microstructure can be altered by adding other elements and heat treatments (HT), which makes the material a promising biomaterial. The Ti-10Mo-Mn alloys were melted in an arc furnace. After ingot casting, a homogenization treatment (#T) was carried out, followed by the mechanical processing of hot rolling (#1) and subsequent annealing HT (#2). This work aimed to analyze the influence of some HT on the phase constituents, percentages, morphologies, distributions and selected mechanical properties, such as microhardness and elastic modulus in Ti-10Mo-xMn system alloys, ranging from 0 to 8% by weight. The results showed that alloys with low manganese content, classified as metastable, were sensitive to the HT in this study. From 4% manganese, the alloys had a stable β phase and were, therefore, not sensitive to the HT. The hardness of the alloys with 0 and 2% manganese remained high, possibly due to the presence of the omega phase. The elastic modulus increased from the hot rolling condition (#1) to annealing condition (#2) in all compositions. The Ti-10Mo-2Mn#1 alloy stood out among the alloys studied. It showed the lowest elastic modulus (~87 GPa), making it suitable for use as a biomaterial.

Thermo doi: 10.3390/thermo5040045

Authors: Pablo Salgado Sánchez Antonio Rosado Lebrón Andriy Borshchak Kachalov Álvaro Oviedo Jeff Porter Ana Laverón Simavilla

This paper describes a laboratory set-up designed to support hands-on learning of heat transfer principles in aerospace engineering education. Developed within the framework of experiential and project-based learning, the set-up enables students to experimentally characterize the convective coefficient of a cooling fan and the thermo-optical properties of aluminum plates with different surface coatings, specifically their absorptivity and emissivity. A custom-built, LED-based radiation source (the ESAT Sun simulator) and a calibrated temperature acquisition system are used to emulate and monitor radiative heating under controlled conditions. Simplified physical models are developed for both the ESAT Sun simulator and the plates that capture the dominant thermal dynamics via first-order energy balances. The laboratory workflow includes real-time data acquisition, curve fitting, and thermal model inversion to estimate the convective and thermo-optical coefficients. The results demonstrate good agreement between the model predictions and observed temperatures, which supports the suitability of the set-up for education. The proposed activities can strengthen the student’s understanding of convective and radiative heat transport in aerospace applications while also fostering skills in data analysis, physical and numerical reasoning, and system-level thinking. Opportunities exist to expand the material library, refine the physical modeling, and evaluate the long-term pedagogical impact of the educational set-up described here.

Thermo doi: 10.3390/thermo5040044

Authors: Serhii Sharapov Danylo Husiev Anton Verbytskiy Roman Vaskin Ivan Kozii Leonid Plyatsuk Iryna Vaskina Dmytro Hopkalo Yuliia Denysenko

This article presents experimental results for motive nozzles with profiled supersonic parts of parabolic, hyperbolic, and elliptical shapes, compared to conical nozzles with unprofiled supersonic parts. This study examined the effect of nozzle geometry and profile on thermodynamic and flow parameters of the vaporization process. The measured parameters included outlet pressure, flow velocity, and mass vapor content, along with dimensionless efficiency indicators, such as relative outflow velocity and the velocity coefficient. Graphical dependencies of these parameters on the relative initial underheating, (1 − εs0), were obtained. This parameter represents the ratio of the pressure difference between inlet and saturation conditions (at inlet temperature) to the inlet pressure. The results show that profiled nozzles operate effectively over a wider range of (1 − εs0) = 0.20–0.45, compared to conical unprofiled nozzles. The vaporization constant for profiled nozzles remained at bn ≈ (2/3)0.5 along their length. The velocity coefficients for profiled designs were 4–6% higher, and the volumetric vapor content at the outlet was also greater, indicating a more efficient vaporization process. Overall, the findings demonstrate that profiling the supersonic section of a motive nozzle improves the operating range, flow characteristics, and vaporization quality compared to conventional conical designs.

Thermo doi: 10.3390/thermo5040043

Authors: Gerardo G. Esquivel-Patiño Fabricio Nápoles-Rivera Arturo Jiménez-Gutiérrez

Biogas has been identified as a sustainable resource of renewable and clean energy because of its social, economic, and environmental benefits. In this work, the analysis of a biogas combined cycle power plant coupled with a carbon capture and utilization (CCU) technology and an organic Rankine cycle (ORC) was considered. The integrated process was subjected to a multi-objective assessment considering energy, economic, environmental, and safety items. The CCU system was taken to produce syngas as a value-added product, and the use of different working fluids for the ORC, namely, R1234yf, R290, and R717, was also examined. Such working fluids were selected to represent options with varying environmental and inherent safety implications. It was shown that the integration of the CCU and ORC components to the biogas cycle plant can provide significant benefits that include a 48.65 kt/year syngas production, a decrease in carbon capture energy penalty by 33%, and a reduction in e-CO2 emissions above 80% with respect to the stand-alone power plant. Comparison with conventional technologies also showed important environmental benefits. The analysis of inherent safety showed that the selection of working fluids for the ORC can have a significant impact on the process risk. From the set of working fluids considered in this work, R717 provided the best choice for the integrated system based on its lowest operational risk and the highest electricity production (355 kWe). The multi-objective approach used in this work allowed the quantification of benefits provided by the integration of CCUs and ORCs with respect to the base process within an overall economic, sustainability, and inherent safety assessment.

Thermo doi: 10.3390/thermo5040042

Authors: Zhenwei Wang Ke An Xueyong Zhou Yingdong Zhu Yuanfu Zhou Linjie Li

This study systematically investigates the variation in the ceiling flame tilt angle in an immersed tube tunnel under the combined effect of longitudinal ventilation and sidewall smoke extraction. The experimental program considers different longitudinal velocities, various sidewall smoke exhaust rates and multiple relative distances between the fire source and the sidewall exhaust outlet, aiming to comprehensively reveal the flame tilt angle under multi-factor coupling conditions. Experiments were carried out in a reduced-scale tunnel model (6.64 m long, 0.96 m wide and 0.5 m high). A porous gas burner supplied a steady heat release, with its distance from the sidewall exhaust outlet systematically varied. Results indicate that the flame tilt angle decreases as the distance between the fire source and the sidewall exhaust outlet increases. A theoretical model was developed to predict the flame tilt angle by incorporating both the sidewall smoke exhaust rate and the relative fire source–exhaust distance. The model accounts for mass loss due to smoke extraction, estimated from the local longitudinal velocity distribution. Predictions from the proposed model agree well with the experimental data.

Thermo doi: 10.3390/thermo5040041

Authors: Flávio S. Pereira Argimiro R. Secchi Alexandre Szklo

The decarbonization of hard-to-defossilize sectors, such as international maritime transport, requires innovative, and at times disruptive, energy solutions that combine efficiency, scalability, and climate benefits. Therefore, power-to-liquid (PtL) routes have stood out for their potential to use low-emission electricity for the production of synthetic fuels, via electrolytic hydrogen and CO2 capture. However, the high energy demand inherent to these routes poses significant challenges to large-scale implementation. Moreover, PtL routes are usually at most neutral in terms of CO2 emissions. This study evaluates, from a thermo-energetic perspective, the optimization potential of an e-methanol synthesis route through integration with a biomass oxy-fuel combustion process, making use of electrolytic oxygen as the oxidizing agent and the captured CO2 as the carbon source. From the standpoint of a first-law thermodynamic analysis, mass and energy balances were developed considering the full oxygen supply for oxy-fuel combustion to be met through alkaline electrolysis, thus eliminating the energy penalty associated with conventional oxygen production via air separation units. The balance closure was based on a small-scale plant with a capacity of around 100 kta of methanol. In this integrated configuration, additional CO2 surpluses beyond methanol synthesis demand can be directed to geological storage, which, when combined with bioenergy with carbon capture and storage (BECCS) strategies, may lead to net negative CO2 emissions. The results demonstrate that electrolytic oxygen valorization is a promising pathway to enhance the efficiency and climate performance of PtL processes.

Thermo doi: 10.3390/thermo5040040

Authors: Huibo Zhang Jinwu Xiang Dawei Bie Daochun Li Zi Kan Lintao Shao Zhi Geng

Hydrogen-powered unmanned aerial vehicles (UAVs) offer significant advantages, such as environmental sustainability and extended endurance, demonstrating broad application prospects. However, the hydrogen fuel cells face prominent thermal management challenges during flight operations. This study established a numerical model of the fuel cell thermal management system (TMS) for a hydrogen-powered UAV. Computational fluid dynamics (CFD) simulations were subsequently performed to investigate the impact of various design parameters on cooling performance. First, the cooling performance of different fan density configurations was investigated. It was found that dispersed fan placement ensures substantial airflow through the peripheral flow channels, significantly enhancing temperature uniformity. Specifically, the nine-fan configuration achieves an 18.5% reduction in the temperature difference compared to the four-fan layout. Additionally, inlets were integrated with the fan-based cooling system. While increased external airflow lowers the minimum fuel cell temperature, its impact on high-temperature zones remains limited, with a temperature difference increase of more than 19% compared to configurations without inlets. Furthermore, the middle inlet exhibits minimal vortex interference, delivering superior thermal performance. This configuration reduces the maximum temperature and average temperature by 9.1% and 22.2% compared to the back configuration.

Thermo doi: 10.3390/thermo5040039

Authors: Barah Ahn Macey Schmetzer Paul I. Ro

The acceleration of climate change and increasing weather-related disasters require more active utilization of renewable energy. To maximize the use of renewable energy, energy storage is an essential part. Liquid piston gas compressors have recently drawn attention because of their applicability to compressed air-based energy storage. Aqueous foam can be used to enhance the efficiency of liquid piston gas compression by boosting heat transfer. To validate the effectiveness of the combination of liquid piston and aqueous foam in a multi-stage compression system, which can contribute to higher efficiency, the present work performed experimental study at various pressure levels. Compressions were performed with and without aqueous foam at three different initial pressure levels of 1, 2, and 3 bars. For each cycle of compression, a pressure ratio of 2 was used, and the impact of pressure levels on compression efficiency was measured. With the use of foam, isothermal efficiencies of 91.4, 88.2, and 86.6% were observed at 1, 2, and 3 bar(s), which improved by 2.2, 2.1, and 1.3% compared to the baseline compressions. To identify the cause of the effectiveness variations, the volume changes in the foam at the different pressure levels were visually compared. In higher-pressure tests, a significant reduction in the foam amount was observed, and this change may contribute to the decreased effectiveness of the technique.

Thermo doi: 10.3390/thermo5040038

Authors: Tianshuo Li Zhenyuan Zhang Guojin Feng Xinhua Chen Ziqi Hao

Infrared thermography for human skin temperature measurement, when calibrated with standard blackbodies, suffers from errors due to the mismatch in emissivity between a blackbody and human skin. This study introduces a novel calibration method utilizing a human skin-like gradient radiation source to enhance measurement accuracy. A custom radiation source with six temperature points and skin-like emissivity was developed. Thermal imagers were calibrated using this source, and their performance was compared against traditional blackbody calibration. The proposed method reduced the calibration error to 0.04 °C, a significant improvement over the 0.15 °C error obtained with blackbody calibration. Calibration with a skin-like radiation source proves superior to the blackbody method, enabling high-accuracy (less than 0.1 °C) human skin temperature measurement for improved fever screening.

Thermo doi: 10.3390/thermo5040037

Authors: María Linares Gisela Orcajo

This study evaluates the impact of using group concept maps in the teaching of Applied Thermodynamics in the Bachelor’s Degree in Industrial Electronics and Automation Engineering. The methodology consisted of selecting topics with a high conceptual load, collaboratively creating concept maps, and subsequently evaluating them by both students and teaching staff. Students achieved average scores above 7/10 in the concept map activity, with teacher and student evaluations averaging 7.8 and 7.3, respectively. Knowledge assessment via pre- and post-tests revealed a 20% increase in concept comprehension. For example, in the topic of Principles of Thermodynamics, the percentage of correct answers on the most complex question increased from 13% in the Pre-Test to 40% in the post-test. In the topic of Refrigeration Cycles, some questions showed an improvement from 18% to 25%. The students’ perception of the activity was positive, with an average satisfaction rating of 6.9 out of 10. Furthermore, most students acknowledged that the activity helped them stay engaged with the subject matter and identify errors in their own learning. The high participation in the activity, despite its low impact on the final grade, demonstrates the students’ strong motivation for this study approach. Therefore, the implementation of concept maps not only facilitated the understanding of key concepts but also promoted critical reflection and collaborative learning, establishing itself as an effective strategy in the teaching of Applied Thermodynamics.

Thermo doi: 10.3390/thermo5030035

Authors: Sagar D Shama Ravichandran Raja Ramar

A novel architectural design is proposed to optimize the thermal management of lithium-ion batteries (LiBs) through a software-enabled switching mechanism. This approach addresses critical challenges such as hot-spot generation, peak temperature rise, and uneven thermal distribution—issues commonly observed in conventional single-terminal battery modules (STBMs). The proposed dual-terminal configuration integrates an enhanced battery pack structure with a software-enabled switching algorithm that identifies the 50% depth of discharge (DoD) and toggles the current path between two terminals to supply the load. Correspondingly, the module also incorporates the division of four thermal zones and four regions concept in the battery module (BM). Experiments were conducted to evaluate the performance of the proposed model at five different C-rates: 0.5C, 0.75C, 1C, 1.25C, and 1.5C. The results demonstrate that the software-enabled dual-terminal switching (Se-DTS) consistently outperforms the STBM across three key aspects. First, in terms of peak temperature, Se-DTS achieved reductions of 19.33%, 17.83%, and 12.72% at C-rates of 1C, 1.25C, and 1.5C, respectively. Second, in thermal distribution, Se-DTS improved performance, with an 86.1% reduction at 1.25C. Third, regarding hot-spot reduction, improvements of 100% (regional level) and 72.22% (zonal level) were observed at 1.25C, while at 1.5C, an 80% improvement was achieved at the zonal level, without using a cooling system.

Thermo doi: 10.3390/thermo5030036

Authors: Alevtina Gosteva Oleg Golubev Vladimir Vinogradov Sergei Svidersky Alena Grabchak Diana Manukovskaya Mihail Ivantsov Mayya Kulikova

The method of obtaining functional materials almost always influences the physicochemical properties of the resulting substances. The plasma treatment of solid materials is considered to be a more energy efficient method when compared with thermal destruction. Our work is the first to treat double complex salt (DCS) [Co(NH3)6][Fe(CN)6] with different plasma discharge modes. We have demonstrated the possibility of obtaining a single-phase spinel with a CoFe2O4 structure as a result of the calcination in air of the plasma destruction product. The crystallite sizes of the obtained spinel are 40 nm, with a lattice constant 8.38 Å.

Thermo doi: 10.3390/thermo5030034

Authors: Fabricio Aguirre Guillermina Luque Gabriel Imwinkelried Fernando Cometto Clara Saux Mariano Teruel María Belén Blanco

The thermal processing of walnut shells was investigated through pyrolysis within the range of 100–650 °C, highlighting the influence of thermal engineering parameters on biomass conversion. The resulting biochar was subjected to chemical activation with phosphoric acid, and its physicochemical properties were evaluated to determine how thermal processing enhances its performance as a cathode material for lithium–sulfur (Li–S) batteries. This approach underscores the role of thermal engineering in bridging biomass valorization with energy storage technologies. In parallel, the gaseous fraction generated during walnut shell fast pyrolysis was collected, and for the first time, volatile organic compounds (VOCs) under atmospheric conditions were identified using solid-phase microextraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS). The composition of the VOCs was characterized, quantifying aromatic compounds, hydrocarbons, furans, and oxygenated species. This study further linked the thermal decomposition pathways of these compounds to their atmospheric implications by estimating tropospheric lifetimes and evaluating their potential contributions to air quality degradation at the local, regional, and global scales.

Thermo doi: 10.3390/thermo5030033

Authors: Mehdi Kabir Corey Field David Howe

To date, two-phase flow boiling has been extensively investigated for various working fluids and geometries, mainly under operating pressures and mass fluxes in the range of medium to high. However, very limited studies have been conducted, focusing on low-pressure low-flow (LPLF) conditions. Given insufficient experimental data available in the literature, most of the existing empirical correlations fail to properly predict boiling heat transfer coefficients (BHTCs) in LPLF conditions, highlighting the need for further experimental investigations. The present study experimentally investigates the heat transfer performance of single-phase and two-phase flow boiling of distilled water in a horizontal conventional tube at constant wall heat flux under LPLF conditions where the operating pressure is set to be subatmospheric and the mass flux ranges below 20 kg/m2-s. For the saturated flow boiling, the effects of mass flux and local vapor quality on the local BHTCs and Nusselt were evaluated, revealing that local BHTCs reach a peak at a certain range of vapor qualities between 55% and 75%, while increasing with the mass flux. It was also found that the impact of mass flux is stronger than that of vapor quality on the local BHTCs. The experimental results in the present study were then compared with several well-known empirical BHTC correlations in the literature to identify those with least deviations under the LPLF conditions. In contrast to single-phase flow, heat loss estimation and vapor quality measurement are known as one of the main error sources in characterizing heat transfer coefficients for two-phase flow boiling. Accordingly, the present study employs two approaches, in parallel, to reliably estimate heat losses, calibrate heat supplies, and measure local vapor qualities under the operating conditions investigated.

Thermo doi: 10.3390/thermo5030032

Authors: Luiz P. B. Braun Rodrigo G. Reis Carlos A. R. Nascimento Alexsandro S. Silveira Christian J. L. Hermes

This study is aimed at evaluating the combined influence of running conditions that affect frost morphology and defrost strategies on the thermal-fluid-dynamic performance of tube-fin ‘no-frost’ evaporators. To this end, two purpose-built experimental apparatuses were designed and constructed, one based upon a fully instrumented two-door bottom-mount ‘combi’ refrigerator with independent temperature and humidity control in both compartments, and another devised specifically for testing evaporator–heater assemblies under controlled frosting and defrosting cycles. Frost accumulation was studied for different surface temperatures and air humidity levels, revealing that higher humidity and lower surface temperatures led to lower frost density and thermal conductivity. Defrosting operations were analyzed for two different psychrometric conditions using three control strategies: step, ramp and pulse-width modulation (PWM). The ramp strategy yielded the highest defrost efficiency, reaching 36.7% in milder frost conditions, while the step strategy led to lower defrosting times. Such findings support the optimization of evaporator design and defrost strategies to improve energy efficiency in household refrigerating appliances.

Thermo doi: 10.3390/thermo5030031

Authors: Igor Donskoy Oleg Khamisov

A usual problem in chemical engineering and fuel processing is to achieve the highest possible efficiency concerning the target products. In this paper, we consider the inverse problem of chemical equilibrium and propose mathematical methods to obtain conditions under which the equilibrium state of the reacting system achieves the required characteristics. For the case of maximising the aim component yield, a new two-step algorithm is developed based on the inverse problem solution. The methods are tested using the methane reforming example.

Thermo doi: 10.3390/thermo5030030

Authors: Tahmid Orville Monem Tajwar Raghav Bihani Parnab Saha Mohammed Abdul Hannan

Over the last several years, a significant advancement in high-voltage electronic packaging techniques has paved the way for next-generation power electronics. However, controlling the thermal properties of these new packaging solutions is still a major challenge. The utilization of wide bandgap semiconductors such as SiC and GaN offers effective methods to minimize thermal inefficiencies caused by conduction losses through high-frequency switching topologies. Nevertheless, the need for high voltage in electrical systems continues to pose significant barriers, as heat generation remains one of the most significant obstacles to widespread implementation. The trend of electronics design miniaturization has driven the development of high-performance cooling concepts to address the needs of high-power-density systems. As a result, the design of effective cooling systems has emerged as a crucial aspect for successful implementation, requiring seamless integration with electronic packaging to achieve optimal performance. This review article explores various thermal management approaches demonstrated in electronic systems. This paper aims to provide a comprehensive overview of heat transfer enhancement techniques employed in electronics thermal management, focusing on core concepts. The review categorizes these techniques into concepts based on fin design, microchannel cooling, jet impingement, phase change materials, nanofluids, and hybrid designs. Recent advancements in high-power density devices, alongside innovative cooling systems such as phase change materials and nanofluids, demonstrate potential for enhanced heat dissipation in power electronics. Improved designs in finned heat sinks, microchannel cooling, and jet impingement techniques have enabled more efficient thermal management in high-density power electronics. By fixing key insights into one reference, this review serves as a valuable resource for researchers and engineers navigating the complex landscape of high-performance cooling for modern electronic systems.

Thermo doi: 10.3390/thermo5030029

Authors: Victor-Eduard Cenușă Ioana Opriș

High-efficiency design solutions for cogeneration steam power plants are studied for different steam consumer requirements (steam pressures between 3.6 and 40 bar and heat flow rates between 10 and 40% of the fuel heat flow rate into the steam generators). Using a genetic algorithm, optimum designs for schemes with extraction-condensing steam turbines, reheat, and supercritical parameters were found considering four objective functions (high global efficiency, low specific investment in equipment, high exergetic efficiency, and high power-to-heat ratio in full cogeneration mode). A second Pareto front was computed from the prior solutions, considering the first two objective functions, resulting in the high-efficiency cogeneration schemes with a primary energy savings (PES) ratio higher than 10%. The results showed that the PES ratio depends strongly on the steam consumer requirements, rising from values under 10% for low heat flow rates and few preheaters to over 25% for a higher number of preheaters, high heat flow rates, and low steam pressures to the consumer. At the same heat flow rate to the consumer, the power-to-heat ratio in full cogeneration mode increases with the decrease in the required steam pressure to the consumer.

Thermo doi: 10.3390/thermo5030028

Authors: Mihaela Constantin Cătălina Dobre Mugurel Oprea

This paper presents a detailed thermodynamic and mathematical modeling study of the oxygenation processes in stationary water bodies, focusing on improving oxygen transfer efficiency, an essential factor in sustaining aquatic ecosystem health. The study employed mathematical models implemented in MATLAB R2024a to simulate the influence of temperature, bubble size, and mass transfer parameters. Key parameters, such as dissolved oxygen concentration, volumetric mass transfer coefficient (akL), and water temperature, were evaluated under different operational scenarios. The oxygenation system was powered by solar energy and included rotating fine-bubble generators mounted on a floating platform. Mathematical modeling carried out in MATLAB validated the theoretical models, showing how environmental factors such as temperature and bubble size influence oxygen dissolution. Initial experimental data, including dissolved oxygen levels (C0 = 3.12 mg/dm3), saturation concentrations at various temperatures (Cs = 8.3 mg/dm3 at 24 °C; Cs = 7.3 mg/dm3 at 30 °C), and a mass transfer coefficient of akL = 0.09 s−1, were used to support the model accuracy. The results highlight the potential of digitally controlled energy-efficient aeration technologies for applications in lake restoration, aquaculture, and sustainable water management. This paper introduces a coupled approach to oxygen transfer and temperature evolution validated experimentally, which has rarely been detailed in the literature. The novelty of this study lies in the combined thermodynamic modeling and exergy–entropy analysis along with real-time tracking, showing the relevance of energy-optimized, digitally monitored oxygenation platforms powered by solar energy.

Thermo doi: 10.3390/thermo5030027

Authors: Paul Rübsamen-v. Döhren Sönke Maus Zhiliang Zhang Jianying He

Ice accretion from marine icing events accumulating on structures poses a significant hazard to ship and offshore operations in cold regions, being relevant for offshore activities like oil explorations, offshore wind, and shipping in arctic regions. The adhesion strength of such ice is a critical factor in predicting the build-up of ice loads on structures. While the adhesion strength of freshwater ice has been extensively studied, knowledge about sea spray ice adhesion remains limited. This study intends to bridge this gap by investigating the adhesion strength of sea spray icing under controlled laboratory conditions. In this study, we built a new in situ ice adhesion test setup and grew ice at −7 °C to −15 °C on quadratic aluminium samples of 3 cm to 12 cm edge length. The results reveal that sea spray ice adhesion strength is in a significantly lower range—5 kPa to 100 kPa—compared to fresh water ice adhesion and shows a low dependency on the temperature during the spray event, but a notable size effect and influence of the brine layer thickness on the adhesion strength. These findings provide critical insights into sea spray icing, enhancing the ability to predict and manage ice loads in marine environments.

Thermo doi: 10.3390/thermo5030026

Authors: Mohamad Kanaan Semaan Amine Mohamed Hmadi

Evaporative cooling (EC) offers an energy-efficient alternative to direct expansion (DX) cooling but suffers from high water consumption. This limitation can be mitigated by pre-cooling incoming fresh air using cooler exhaust air via energy recovery. This study presents and optimizes a solar-driven EC system integrated with underfloor air distribution (UFAD) to enhance thermal comfort and minimize water use in a temporary office in Riyadh’s arid climate. A 3D CFD model was developed and validated against published data to simulate indoor airflow, providing data for thermal comfort evaluation using the predicted mean vote model in cases with and without energy recovery. A year-round hourly energy analysis revealed that the solar-driven EC-UFAD system reduces grid power consumption by 93.5% compared to DX-based UFAD under identical conditions. Energy recovery further cuts annual EC water usage by up to 31.3%. Operational costs decreased by 84% without recovery and 87% with recovery versus DX-UFAD.

Thermo doi: 10.3390/thermo5030025

Authors: Ivan R. Kennedy Migdat Hodzic Angus N. Crossan

Atmospheric climate science lacks the capacity to integrate thermodynamics with the gravitational potential of air in a classical quantum theory. To what extent can we identify Carnot’s ideal heat engine cycle in reversible isothermal and isentropic phases between dual temperatures partitioning heat flow with coupled work processes in the atmosphere? Using statistical action mechanics to describe Carnot’s cycle, the maximum rate of work possible can be integrated for the working gases as equal to variations in the absolute Gibbs energy, estimated as sustaining field quanta consistent with Carnot’s definition of heat as caloric. His treatise of 1824 even gave equations expressing work potential as a function of differences in temperature and the logarithm of the change in density and volume. Second, Carnot’s mechanical principle of cooling caused by gas dilation or warming by compression can be applied to tropospheric heat–work cycles in anticyclones and cyclones. Third, the virial theorem of Lagrange and Clausius based on least action predicts a more accurate temperature gradient with altitude near 6.5–6.9 °C per km, requiring that the Gibbs rotational quantum energies of gas molecules exchange reversibly with gravitational potential. This predicts a diminished role for the radiative transfer of energy from the atmosphere to the surface, in contrast to the Trenberth global radiative budget of ≈330 watts per square metre as downwelling radiation. The spectral absorptivity of greenhouse gas for surface radiation into the troposphere enables thermal recycling, sustaining air masses in Lagrangian action. This obviates the current paradigm of cooling with altitude by adiabatic expansion. The virial-action theorem must also control non-reversible heat–work Carnot cycles, with turbulent friction raising the surface temperature. Dissipative surface warming raises the surface pressure by heating, sustaining the weight of the atmosphere to varying altitudes according to latitude and seasonal angles of insolation. New predictions for experimental testing are now emerging from this virial-action hypothesis for climate, linking vortical energy potential with convective and turbulent exchanges of work and heat, proposed as the efficient cause setting the thermal temperature of surface materials.

Thermo doi: 10.3390/thermo5030024

Authors: Ayah Marwan Rabi’ Jovana Radulovic James M. Buick

In recent years, packed-bed systems have emerged as an attractive design for thermal energy storage systems due to their high thermal efficiency and economic feasibility. As integral components of numerous large-scale applications systems, packed-bed thermal energy stores can be successfully paired with renewable energy and waste heat to improve energy efficiency. An analysis of the thermal performances of two packed beds (hot and cold) during six-hour charging and discharging cycles has been conducted in this paper using COMSOL Multiphysics software, utilizing the optimal design parameters that have been determined in previous studies, including porosity (0.2), particle diameters (4 mm) for porous media, air as a heat transfer fluid, magnesia as a storage medium, mass flow rate (13.7 kg/s), and aspect ratio (1). The performance has been evaluated during both the charging and discharging cycles, in terms of the system’s capacity factor, the energy stored, and the thermal power, in order to understand the system’s performance and draw operational recommendations. Based on the results, operating the hot/cold storage in the range of 20–80% of the full charge was found to be a suitable range for the packed-bed system, ensuring that the charging/discharging power remains within 80% of the maximum.

Thermo doi: 10.3390/thermo5030023

Authors: Abir El Abed Ghalia Nassreddine Obada Al-Khatib Mohamad Nassereddine Ali Hellany

Modern energy storage systems for both power and transportation are highly related to lithium-ion batteries (LIBs). However, their safety depends on a potentially hazardous failure mode known as thermal runaway (TR). Predicting and classifying TR causes can widely enhance the safety of power and transportation systems. This paper presents an advanced machine learning method for forecasting and classifying the causes of TR. A generative model for synthetic data generation was used to handle class imbalance in the dataset. Hyperparameter optimization was conducted using Optuna for four classifiers: Support Vector Machine (SVM), Multi-Layer Perceptron (MLP), tabular network (TabNet), and Extreme Gradient Boosting (XGBoost). A three-fold cross-validation approach was used to guarantee a robust evaluation. An open-source database of LIB failure events is used for model training and testing. The XGBoost model outperforms the other models across all TR categories by achieving 100% accuracy and a high recall (1.00). Model results were interpreted using SHapley Additive exPlanations analysis to investigate the most significant factors in TR predictors. The findings show that important TR indicators include energy adjusted for heat and weight loss, heater power, average cell temperature upon activation, and heater duration. These findings guide the design of safer battery systems and preventive monitoring systems for real applications. They can help experts develop more efficient battery management systems, thereby improving the performance and longevity of battery-operated devices. By enhancing the predictive knowledge of temperature-driven failure mechanisms in LIBs, the study directly advances thermal analysis and energy storage safety domains.

Thermo doi: 10.3390/thermo5030022

Authors: Akram Kharmouch Md. Kamrul Hasan El Yatim Sabik Hicham Bouali Hayati Mamur Mohammad Ruhul Amin Bhuiyan

Cryosurgery employs extremely low temperatures to destroy abnormal or cancerous tissue. Conventional systems use cryogenic fluids like liquid nitrogen or argon, which pose challenges in handling, cost, and precise temperature control. This study explores thermoelectric (TE) cooling using the Peltier effect as an efficient alternative. A numerical optimization of multi-stage TE coolers using bismuth telluride (Bi2Te3) is performed through finite element analysis in COMSOL Multiphysics. Results show that the optimized multi-stage TE system achieves a minimum temperature of −70 °C, a 90 K temperature difference, and 4.0 W cooling power—outperforming single-stage (SS) systems with a maximum ΔT of 73.27 K. The study also investigates the effects of material properties, current density, and geometry on performance. An optimized multi-stage (MS) configuration improves cooling efficiency by 22.8%, demonstrating the potential of TE devices as compact, energy-efficient, and precise solutions for cryosurgical applications. Future work will explore advanced nanomaterials and hybrid systems to further improve performance in biomedical cooling.

Thermo doi: 10.3390/thermo5030021

Authors: Peter Futas Alena Pribulova Jozef Petrik Peter Blasko Marek Solc Marcin Brzezinski

Cast iron is a longtime reliable material for the production of heat-treated stressed castings, i.e., those that are long, are cyclically heated, and heat-stressed. The durability of thermally stressed castings used in practice is dependent on the choice of the optimum chemical composition, metallurgy of production, macro- and microstructures, construction, and the way of exploitation. Today, the successful solution of this problem is dominated by simulation programs. The comprehensive analysis of heat stress is very important, i.e., the impacts of various physical quantities on its rise, progress, and size. This paper provides a comprehensive analysis of thermal stress mechanisms in gray iron castings, with a particular emphasis on the relationships between the material properties, microstructural characteristics, and component performance under thermal loading conditions. The theoretical foundations are complemented by experimental data, establishing practical guidelines for optimizing cast iron compositions and processing parameters for thermal applications.

Thermo doi: 10.3390/thermo5020020

Authors: Vassilis P. Panoskaltsis

Based on the First and the Second laws of Thermodynamics the energy dissipated in engineering materials and structures is calculated in a multidimensional mechanics framework. The existing practice of computing the dissipated energy by the area of the stress-strain (or force-displacement) curve is objected to. The conditions under which the area of a stress-strain diagram correctly measures the dissipated energy are derived and clearly presented. A general mathematical form for the dissipated energy when those conditions are not satisfied is provided. An internal variables formulation is employed in this work. Erroneous results from the literature calculating the dissipated energy are given. Erroneous calculations are abundant in publications, Theses and Dissertations, books, and even engineering codes. The terms hysteresis and hysteretic loss are technically explained and their wrong use in cases other than in viscoelasticity is explicated.

Thermo doi: 10.3390/thermo5020019

Authors: Onawale O. Tairu Olusegun O. Ajide Olawale S. Ismail Olanrewaju M. Oyewola

This study investigates the effects of varying hydrogen percentages in fuel blends on combustion dynamics, engine performance, and emissions. Experimental data and analytical equations were used to evaluate combustion parameters such as equivalent lambda, in-cylinder pressure, heat release rate, and ignition timing. The findings demonstrate that hydrogen blending enhances combustion stability, shortens ignition delay, and shifts peak heat release to be closer to the top dead center (TDC). These changes improve thermal efficiency and reduce cycle-to-cycle variation. Hydrogen blending also significantly lowers carbon dioxide (CO2) and hydrocarbon (HC) emissions, particularly at higher blend levels (H0–H5), while lower blends increase nitrogen oxides (NOx) emissions and risk pre-ignition due to advanced start of combustion (SOC). Engine performance improved with an average hydrogen energy contribution of 12% under a constant load. However, the optimal hydrogen blending range is crucial to balancing efficiency gains and emission reductions. These results underline the potential of hydrogen as a cleaner additive fuel and the importance of optimizing blend ratios to harness its benefits effectively.

Thermo doi: 10.3390/thermo5020018

Authors: Arnaud Nzendjang Mbakouop Claude Bertin Nzoundja Fapi André Désire Siéwé Hyacinthe Tchakounté Awoh Innocentia Ankungha

A crucial stage in the post-harvest processing of cocoa beans, drying, has a direct effect on the finished product’s quality and market value. This study investigates the efficiency, quality outcomes, and environmental implications of a mixed forced convection solar dryer designed for drying cocoa beans in Ntui, Cameroon, compared to traditional open-air drying methods. The solar dryer’s design, incorporating a solar collector, forced ventilation, and thermal storage, leverages local materials and renewable energy, offering an environmentally sustainable alternative by reducing fossil fuel reliance and post-harvest losses. Experimental trials were conducted to assess key drying parameters, including the temperature, relative humidity, water removal rate, pH, and free fatty acid (FFA) content, under the equatorial climate conditions of high solar irradiation and humidity. Results demonstrate that the solar dryer significantly reduces drying time from an average of 4.83 days in open-air drying to 2.5 days, a 50% improvement, while maintaining optimal conditions for bean quality preservation. The solar-dried beans exhibited a stable pH (5.7–5.9), a low FFA content (0.282% oleic acid equivalent, well below the EU standard of 1.75%), and superior uniformity in texture and color, meeting international quality standards. In contrast, open-air drying showed greater variability in quality due to weather dependencies and contamination risks. The study highlights the dryer’s adaptability to equatorial climates and its potential to enhance cocoa yields and quality for small-scale producers. These findings underscore the viability of solar drying as a high-performance, eco-friendly solution, paving the way for its optimization and broader adoption in cocoa-producing regions. This research contributes to the growing body of knowledge on sustainable drying technologies, addressing both economic and environmental challenges in tropical agriculture.

Thermo doi: 10.3390/thermo5020017

Authors: Xing Wang Chun Wang Jiangjun Zhu Huizhao Wang Chenxi Dai Li Sun

In the age of widespread renewable energy integration, coal-fired power plants are transitioning from a primary baseload role to a more flexible peak-shaving capacity. Under frequent load changes, the thermal efficiency will significantly decrease. In order to achieve efficient dynamic operation, this study proposes a comprehensive mechanical model of a 300 MW drum-type boiler. Based on the Modelica/DYMOLA platform, the multi-domain equations describing energy and mass balance are programmed and solved. A comprehensive evaluation of the energy transformation within the boiler’s heat exchange components was performed. Utilizing the principles of exergy analysis, this study investigates how fluctuating operational conditions impact the energy dynamics and exergy losses in the drum and heating surfaces. Steady-state simulation reveals that the evaporator and superheater units account for 81.3% of total exergy destruction. Dynamic process analysis shows that the thermal inertia induced by the drum wall results in a significant delay in heat transfer quantity, with a dynamic period of up to 5000 s. The water wall exhibits the highest total dynamic exergy destruction at 9.5 GJ, with a destruction rate of 7.9–8.5 times higher than other components.

Thermo doi: 10.3390/thermo5020016

Authors: William Keeley Richard Turner Bashir Mitchell Nils Warnken

Thermal modelling of additive manufacturing is a key method for furthering the quality of the components produced, as it allows for analysis that is not possible via experimental methods due to the difficulties involved with in situ monitoring. The thermal gradients present during the additive manufacturing process have a large impact on the formation of defects, such as porosity, residual stress, and cracking. The thermal gradients also have a large impact on material properties by controlling the microstructure formed. Thermal modelling methods are often based on numerical solutions of the heat conduction equation. Whilst numerical methods can be more accurate, they are often very slow because of the fine mesh requirements to capture high thermal gradients and iterative solvers to approximate the real-world solution to the required thermal field equations. An analytical model was developed to provide a fast solution to the problem. The analytical model used in this research was based on the Rosenthal equation and was analysed under a range of process parameters. A temperature-dependent Rosenthal model was also created with the aim of improving the results. The analytical model was then compared with a finite element numerical model to act as verification for the results. The analytical model accurately predicted the meltpool width over a range of process conditions. The analytical model underestimated the meltpool length compared to the numerical model, especially at high velocities. When using the standard Rosenthal model, the use of room-temperature or high-temperature thermal conductivities underestimated or overestimated the cooling rates from the meltpool, respectively. A temperature-dependent Rosenthal model was shown to produce more accurate cooling rates compared to the original Rosenthal equation.

Thermo doi: 10.3390/thermo5020015

Authors: Muhammad Sajjad Muhammad Zahid Mumtaz A. Qaisrani

Passive solar desalination with no discharge promises great potential for sustainable desalination. Herein, we provide a comprehensive modelling scheme for the investigation of coupled heat and mass transport in passive desalination devices. Our modelling approach integrates mass, momentum, species, and energy transport models to study the coupled phenomena of wicking, solar-driven evaporation, and salt precipitation. Our numerical model can predict the impact of spatiotemporal variation in temperature, salt concentration, and wicking velocity on the evaporation flux and thermal efficiency of solar evaporators. The impact of the evaporator’s shape, solar flux, salt concentration, and light reflection by salt crystals has been studied on the evaporator’s performance. We observed a two-fold increase in evaporation flux when solar irradiance increases from 1000 W/m2 to 2500 W/m2. A reduction in the thermal efficiency of the evaporators is predicted at higher solar fluxes. The modelled evaporator can achieve an evaporation flux of over 0.5 kg/m2h under 1000 W/m2 for 3.5 wt.% saline water. The salt concentration along the z-position of the evaporator exhibited a double arch-shaped profile, which influences its evaporation performance. These findings provide vital guidelines for the design of high-throughput solar desalination systems.

Thermo doi: 10.3390/thermo5020014

Authors: Alice Cavalerie Jasmin Raymond Louis Gosselin Jean Rouleau Ali Hakkaki-Fard

Energy transition is a challenge for remote northern communities mainly relying on diesel for electricity generation and space heating. Solar-assisted ground-coupled heat pump (SAGCHP) systems represent an alternative that was investigated in this study for the Kuujjuaq Forum, a multi-activity facility in Nunavik, Canada. The energy requirements of community buildings facing a subarctic climate are poorly known. Based on energy bills, technical documents, and site visits, this study provided an opportunity to better document the energy consumption of such building, especially considering the recent solar photovoltaic (PV) system installed on part of the roof. A comprehensive model was developed to analyze the building’s heating demand and simulate the performance of a ground-source heat pump (GSHP) coupled with PV panels. The air preheating load, accounting for 268,200 kWh and 47% of the total heating demand, was identified as an interesting and realistic load that could be met by SAGCHP. The GSHP system would require a total length of at least 8000 m, with boreholes at depths between 170 and 200 m to meet this demand. Additional PV panels covering the entire roof could supply 30% of the heat pump’s annual energy demand on average, with seasonal variations from 22% in winter to 53% in spring. Economic and environmental analysis suggest potential annual savings of CAD 164,960 and 176.7 tCO2eq emissions reduction, including benefits from exporting solar energy surplus to the local grid. This study provides valuable insights on non-residential building energy consumption in subarctic conditions and demonstrates the technical viability of SAGCHP systems for large-scale applications in remote communities.

Thermo doi: 10.3390/thermo5020013

Authors: Reem Alzubaidi Makram A. Fakhri László Pohl

In this study, a thin film of silicon carbide (SiC) was deposited on a porous silicon (P-Si) substrate using pulsed laser deposition (PLD). The photo–electrochemical etching method with an Nd: YAG laser at 1064 nm wavelength and 900 mJ pulse energy and at a vacuum of 10−2 mbar P-Si was utilized to create a sufficiently high amount of surface area for SiC film deposition to achieve efficient SiC film growth on the P-Si substrate. X-ray diffraction (XRD) analysis was performed on the crystalline structure of SiC and showed high-intensity peaks at the (111) and (220) planes, indicating that the substrate–film interaction is substantial. Surface roughness particle topography was examined via atomic force microscopy (AFM), and a mean diameter equal to 72.83 nm was found. Field emission scanning electron microscopy (FESEM) was used to analyze surface morphology, and the pictures show spherical nanoparticles and a mud-sponge-like shape demonstrating significant nanoscale features. Photoluminescence and UV-Vis spectroscopy were utilized to investigate the optical properties, and two emission peaks were observed for the SiC and P-Si substrates, at 590 nm and 780 nm. The SiC/P-Si heterojunction photodetector exhibited rectification behavior in its dark I–V characteristics, indicating high junction quality. The spectral responsivity of the SiC/P-Si observed a peak responsivity of 0.0096 A/W at 365 nm with detectivity of 24.5 A/W Jones, and external quantum efficiency reached 340%. The response time indicates a rise time of 0.48 s and a fall time of 0.26 s. Repeatability was assured by the tight clustering of the data points, indicating the good reproducibility and stability of the SiC/P-Si deposition process. Linearity at low light levels verifies efficient photocarrier generation and separation, whereas a reverse saturation current at high intensities points to the maximum carrier generation capability of the device. Moreover, Raman spectroscopy and energy dispersive spectroscopy (EDS) analysis confirmed the structural quality and elemental composition of the SiC/P-Si film, further attesting to the uniformity and quality of the material produced. This hybrid material’s improved optoelectronic properties, achieved by combining the stability of SiC with the quantum confinement effects of P-Si, make it useful in advanced optoelectronic applications such as UV-Vis photodetectors.

Thermo doi: 10.3390/thermo5010012

Authors: Johan Jacquemin

As we embark on a new chapter in 2025, it is with immense pride and gratitude that we reflect on the remarkable journey of Thermo (ISSN 2673-7264; [...]

Thermo doi: 10.3390/thermo5010011

Authors: Luísa Amaral Manuel Ribeiro da Silva

The thermochemical properties of three sulfur-containing furan derivatives, 2-furanmethanethiol, furfuryl methyl sulfide, and methyl 2-methyl-3-furyl disulfide, were investigated using experimental and theoretical methods. Standard molar enthalpies of combustion were determined by combustion calorimetry, while enthalpies of vaporization were obtained through Calvet microcalorimetry. These experimental results allowed for the calculation of standard molar enthalpies of formation in the gas phase at 298.15 K. Theoretical calculations using high-level quantum chemical methods (G3) were performed to complement the experimental data. A comparison between experimental and theoretical values revealed good agreement, validating the computational approach. This study enhances the understanding of the energetic properties of sulfur furan derivatives, contributing reliable thermochemical data to existing databases and aiding in the development of predictive models for related molecular systems.

Thermo doi: 10.3390/thermo5010010

Authors: Gergely Balázs Patthy Zsófia Závodi-Fodor Miklós Jakab

The growing volume of end-of-life photovoltaic (PV) panels, projected to reach 60–78 million tons by 2050, poses significant environmental challenges. With landfilling being the most cost-effective but unsustainable disposal method, developing eco-friendly processes to recover valuable materials is essential. One potential solution for recovering raw materials from PV panels is thermal treatment. Therefore, in this study, PV modules were heat-treated at a low heating rate, and their components were manually separated with an average efficiency of 90%. The recovered silicon wafers and tempered glass sheets were utilized to fabricate new PV panels using lamination technology. The applied heating parameters enabled the cells to be removed from the PV panels without structural damage. However, the results of electroluminescence tests showed that thermal treatment significantly damages the p-n junctions, rendering direct reuse in new panels unfeasible. The thermal separation methods outlined in this study offer valuable opportunities for industries employing various PV-panel-recycling technologies. These methods lay the groundwork for environmentally responsible management and recovery of materials from end-of-life solar panels, advancing sustainable recycling practices.

Thermo doi: 10.3390/thermo5010009

Authors: Francesco Calise Francesco Liberato Cappiello Luca Cimmino Massimo Dentice d’Accadia Maria Vicidomini

This study addresses the critical challenge of performing a detailed calculation of energy savings in buildings by implementing suitable actions aiming at reducing greenhouse gas emissions. Given the high energy consumption of buildings’ space heating systems, optimizing their performance is crucial for reducing their overall primary energy demand. Unfortunately, the calculations of such savings are often based on extremely simplified methods, neglecting the dynamics of the emitters installed inside the buildings. These approximations may lead to relevant errors in the estimation of the possible energy savings. In this framework, the present study presents a novel 0-dimensional capacitive model of a radiator, the most common emitter used in residential buildings. The final scope of this paper is to integrate such a novel model within the TRNSYS 18simulation environment, performing a 1-year simulation of the overall building-space heating system. The radiator model is developed in MATLAB 2024b and it carefully considers the impact of surface area, inlet temperature, and flow rate on the radiator performance. Moreover, the dynamic heat transfer rate of the capacitive radiator is compared with the one returned by the built-in non-capacitive model available in TRNSYS, showing that neglecting the capacitive effect of radiators leads to an incorrect estimation of the heating consumption. During the winter season, with a heating system turned on from 8 a.m. to 4 p.m. and from 6 p.m. to 8 p.m., the thermal energy is underestimated by roughly 20% with the commonly used non-capacitive model.

Thermo doi: 10.3390/thermo5010008

Authors: Efstathios E. Michaelides

Carbon capture and sequestration have been recently presented as a viable option to reduce atmospheric carbon dioxide emissions and mitigate global climate change. The concept entails the capture, compression, transportation, and injection of the gas into a medium suitable for storage. This paper examines the thermodynamic and transport properties of carbon dioxide that are pertinent to its sequestration and storage, describes the various methods that have been recommended for its separation from the mixture of the flue gases, and determines the mechanical power and heat rate required for the capture of the gas. The power required for the compression and transportation of the gas by a pipeline is also determined, as well as the effect of the ambient temperature on the transportation power. Calculations for the total power required are performed for two cases, one a cement production unit and the second a coal power plant. The mechanical power needed for the sequestration of CO2 is substantial in both cases, with the cement unit needing less power because of the availability of high-temperature waste heat. In both cases, the equivalent mechanical work needed for the sequestration and storage of this gas is on the order of 1 MJ per kg CO2 sequestered.

Thermo doi: 10.3390/thermo5010007

Authors: Krishna Kota Sarada Kuravi Prasanna Jayaramu

This study explored the relationship between the Nusselt number and the friction factor in the laminar boundary slip flow of a Newtonian liquid between parallel plates. In addition, simplified equations were developed to estimate two key parameters—slip velocity and temperature jump—both of which are typically difficult to measure in experimental settings. The primary objectives of investigating the relationship between the Nusselt number and the friction factor were twofold: (1) to uncover the previously unknown mathematical connection (or analogy) between momentum transfer and heat transfer in the presence of boundary slip and (2) to enable predictions of either the pressure drop or the heat transfer coefficient by measuring just one of these quantities, thus simplifying experimental procedures. Considering the difficulty of conducting experiments of this type of flow (as described in the published literature), a finite element-based numerical model built in COMSOL Multiphysics software was used to validate the theoretically developed relationship over a wide range of Reynolds numbers and boundary slip values. While surface modifications like dimples, bumps, and ribs typically modify both the Nusselt number and pressure drop, leading to their increase for a given fluid and constant inlet Reynolds number, their behavior changes when boundary slip is present, particularly in cases where there is a low temperature jump at the wall. The analysis identified a specific threshold for the dimensionless temperature jump below which the Nusselt number with boundary slip will exceed 8.235. Furthermore, the analysis showed that for the Nusselt number to rise above 8.235, the non-dimensional velocity slip must be at least 3.19 times larger than the non-dimensional temperature jump. This means that the velocity slip has to be significantly larger than the temperature jump to achieve enhanced heat transfer in boundary slip flows.

Thermo doi: 10.3390/thermo5010006

Authors: Lina Ju Peng Jiang Xing Zhou Ruiwen Liu Yanmei Kong Yuxin Ye Binbin Jiao Honglin Sun Fan Wei

When chips perform numerous computational tasks or process complex instructions, they generate substantial heat, potentially affecting their long-term reliability and performance. Thus, accurate and effective temperature measurement and management are crucial to ensuring chip performance and lifespan. This paper presents a multi-channel temperature measurement system based on a diode temperature-sensitive array thermal test chip (TTC). The thermal test chip accurately emulates the heat power and thermal distribution of the target chip, providing signal output through row and column address selection. The multi-channel temperature measurement system centers around a microcontroller and includes voltage signal acquisition circuits and host computer software. It enables temperature acquisition, storage, and real-time monitoring of 16 channels in a 4 × 4 array thermal test chip. During experiments, the system uses a constant current source to drive temperature-sensitive diodes, collects diode output voltage through multiplexers and high-precision amplification circuits, and converts analog signals to digital signals via a high-speed ADC. Data transmission occurs via the USB 2.0 protocol, with the host computer software handling data processing and real-time display. The test results indicate that the system accurately monitors chip temperature changes in both steady-state and transient thermal response tests, closely matching measurements from a semiconductor device analyzer, with an error of about 0.67%. Therefore, this multi-channel temperature measurement system demonstrates excellent accuracy and real-time monitoring capability, providing an effective solution for the thermal design and evaluation of high power density integrated circuits.

Thermo doi: 10.3390/thermo5010005

Authors: Tarik Boushaki Kacem Mansouri

Gas turbines are widely used in power generation due to their efficiency, flexibility, and low environmental impact. Modeling, especially in thermodynamics, is crucial for the designer and operator of a gas turbine. An advanced and rigorous thermodynamic model is essential to accurately predict the performance of a gas turbine under on-design operating conditions, off-design or failure. Such models not only improve understanding of internal processes but also optimize performance and reliability in a wide variety of operational scenarios. This article presents the development of a thermodynamic model simulating the off-design performance of a gas turbine. The mathematical relationships established in this model allow for quick calculations while requiring a limited amount of data. Only nominal data are required, and some additional data are needed to calibrate the model on the turbine under study. A key feature of this model is the development of an innovative relationship that allows direct calculation of the mass flow of air entering the turbine and, thus, the performances of the turbine according to atmospheric conditions (such as pressure, temperature, and relative humidity) and the position of the compressor inlet guide vanes (IGV). The results of the simulations, obtained using code implemented in MATLAB (R2014a), demonstrate the efficiency of the model compared to experimental data. Indeed, the model relationships exhibit high determination coefficients (R2 > 0.95) and low root mean square errors (RMSE). Specifically, the simulation results for the air mass flow rate demonstrate a very high determination coefficient (R2 = 0.9796) and a low root mean square error (RMSE = 0.0213).

Thermo doi: 10.3390/thermo5010004

Authors: Chao Zhang Xinbin Ma Mengxi Li Yubin Qiu Moon Keun Kim Jiying Liu

The accurate assessment of parameters such as burn degree, volume, and depth is a prerequisite for the effective treatment of patients. However, as an unsteady heat transfer process, the temperature of the burn damage volume changes over time, and it is difficult to accurately calculate the integral value of the damage, which is used to assess the burn degree. Therefore, it is impossible to accurately determine the location and volume of damage at all burn degrees. In this study, the C language is used to program a user-defined function of the burn damage integral formula, and the coupled numerical simulation method is used to calculate the heat transfer and damage in a high-temperature water burn process. Then, the temperature and burn damage integral value of each point can be determined to accurately assess and distinguish the burn degree in real time, and estimate the position distribution, volume size, and transient change trend of each burn degree. Under the working conditions selected in this paper, the heat source mainly affects the epidermis and dermis directly below, and has less influence on the area above, which is in convective heat transfer. The damage integral value is very sensitive to temperature, and the highest damage integral value caused by 373 K is two and four orders of magnitude higher than that of 363 K and 353 K, respectively. The increase in the heat source temperature caused the volume of a third-degree burn to increase rapidly in the early stage of injury, but the volume of second-degree and first-degree burns did not change much. After heating at 373 K for 15 s and delaying the action for 45 s, the volume of first-, second-, and third-degree burns accounted for 0.4, 2.9, and 1.9%, respectively, and the total volume of damage accounted for only 5.2% of the total volume.

Thermo doi: 10.3390/thermo5010003

Authors: Heba Alzaben Roydon Fraser

The second law of thermodynamics investigates the quality of energy, or in other words exergy, described as the maximum useful to the dead-state work. The objective of this paper is to investigate the energy and exergy flows in a crop plant system in order to identify the dominant flows and parameters (e.g., temperature) affecting crop plant development. The need for energy and exergy analyses arises from the hypothesis that crop stress can be detected via surface temperature measurements, as explained by the exergy destruction principle (EDP). Based on the proposed energy model, it is observed that radiation and transpiration terms govern all other terms. In addition, as a result of exergy analysis, it is observed that solar exergy governs all input and output terms. The results obtained from this study support the hypothesis that crop surface temperature can be utilized as an indicator to detect crop stress.

Thermo doi: 10.3390/thermo5010002

Authors: Ayah Marwan Rabi’ Jovana Radulovic James M. Buick

In the original publication [...]

Thermo doi: 10.3390/thermo5010001

Authors: Victor-Eduard Cenușă Ioana Opriș

Steam thermal power plants represent important energy production systems. Within the energy mix, these could allow flexible generation and the use of hybrid systems by integrating renewables. The optimum design solution and parameters allow higher energy efficiency and lower environmental impact. This paper analyzes single reheat supercritical steam power plants design solutions using a genetic heuristic algorithm. A multi-objective optimization was made to find the Pareto frontier that allows the maximization of the thermal cycle net efficiency and minimization of the specific investment in the power plant equipment. The Pareto population was split and analyzed depending on the total number of preheaters. The mean values and the standard deviations were found for the objective functions and main parameters. For the thermal cycle schemes with eight preheaters, the average optimal thermal cycle efficiency is (48.09 ± 0.16)%. Adding a preheater increases the average optimal thermal cycle efficiency by 0.64%, but also increases the average optimum specific investments by 7%. It emphasized the importance of choosing a proper ratio between the reheating and the main steam pressure. Schemes with eight and nine preheaters have an average optimum value of 0.178 ± 0.021 and 0.220 ± 0.011, respectively. The results comply with data from the literature.

Thermo doi: 10.3390/thermo4040028

Authors: Fabio Peluso

In this paper, a reliable model of the viscosity in liquids in the dual model of liquids (DML) framework is developed. The analytical expression arrived at exhibits the correct T–dependence Arrhenius-like exponential decreasing trend, which is typical of Newtonian simple fluids. The model is supported by the successful comparison with both the experimental values of the viscosity of water, and with those related to the mechano-thermal effect in liquids under low-frequency shear, discovered a few years ago, for which the first-ever theoretical interpretation is given by the DML. Moreover, the approach is even supported by the results of numerical models recently developed, that have shown that dual liquid models, such as the DML, provides very good agreement with experimental data. The expression of viscosity contains terms belonging to both the subsystems constituting the liquid, and shows an explicit dependence upon the sound velocity and the collective vibratory degrees of freedom (DoF) excited at a given temperature. At the same time, the terms involved depend upon the Boltzmann and Planck constants. Finally, the physical model is coherent with the Onsager postulate of microscopic time reversibility as well as with time’s arrow for macroscopic dissipative mechanisms.

Thermo doi: 10.3390/thermo4040027

Authors: Mamoun Clévie Aboni Akodzi Pierre Girods Timoléon Andzi-Barhé Yann Rogaume

A kinetic model based on the two-stage semi-global multi-reaction model of Grioui was developed using the TG and DTG curves for the by-products of Kambala and Ayous. These two tropical species are widely used in the Republic of Congo. The TG and DTG curves were obtained through thermogravimetry at five different heating rates (3, 7, 10, and 20 K/min) up to a final temperature of 800 °C under a nitrogen atmosphere. The thermal decomposition of both species started at similar temperatures, but the profiles exhibited notable differences. Kambala showed a distinct profile with two peaks at approximately 500 °C and 700 °C, which upon further investigation were found to correspond to ash decomposition. Additionally, the shoulder present in Ayous between 250 °C and 300 °C, attributed to hemicelluloses degradation, was absent in the DTG curves for Kambala. The kinetic model for Ayous was formulated in three steps, while the model for Kambala consisted of four steps. Both models accurately predicted the thermal degradation of the wood species, and the resulting kinetic parameters aligned with those reported in the literature.

Thermo doi: 10.3390/thermo4040026

Authors: Mario García-González Guanggui Cheng Duc Thuan Bui Josué Aarón López-Leyva

Due to modern comfort demands and global warming, heating, ventilation, and air conditioning (HVAC) systems are widely used in many homes and buildings. However, HVAC based on the Vapor Compression System (VCS) is a major energy consumer, accounting for 20–50% of a building’s energy consumption and responsible for 29% of the world’s CO2 emissions. Dew-point evaporative coolers offer a sustainable alternative yet face challenges, e.g., dew point and wet bulb effectiveness. Given the above, dew point evaporative cooling systems may find a place to dethrone conventional air conditioning systems. This research aims to design a dew point evaporative cooler system with better performance in terms of dew point and wet bulb effectiveness. In terms of methodology, a heat exchanger as part of a counter-flow dew point cooling system was designed and analyzed using COMSOL simulations under different representative climatic, geometric, and dimensional conditions, taking into account turbulent flow. Next, our model was compared with other cooling systems. The results show that our model performs similarly to other cooling systems, with an error of around 6.89% in the output temperature at low relative humidity (0–21%). In comparison, our system is more sensitive to humidity in the climate, whereas heat pumps can operate in high humidity. The average dew point and wet bulb effectiveness were also higher than reported in the literature, at 91.38% and 147.84%, respectively. In addition, there are some potential limitations of the simulations in terms of the assumptions made about atmospheric conditions. For this reason, the results cannot be generalized but must be considered as a starting point for future research and technology development projects.

Thermo doi: 10.3390/thermo4040025

Authors: Claudia Ongil Úrsula Martínez Pablo Salgado Sánchez Andriy Borshchak Kachalov Jose Miguel Ezquerro Karl Olfe

Here, we investigate the performance of phase-change materials (PCMs) in the passive thermal control of space habitats. PCMs are able to absorb and release large amounts energy in the form of latent heat during their (typically, solid-to-liquid) phase transition, which makes them an ideal choice for passive temperature control. In this study, a conceptual design of an igloo-shaped habitat is proposed. A scaled model for laboratory experiments is manufactured via 3D printing, using tap water as the PCM. The setup is used to conduct experiments and analyze PCM performance, based on temperature measurements inside and outside the habitat. Results demonstrate the effectiveness of PCMs in increasing thermal inertia and stabilizing the habitat interior temperature around the melting temperature, confirming that PCMs can be a suitable alternative for passive thermal control. The present study holds significant interest for the future of space exploration, with the emerging need to design habitats that are capable of accommodating astronauts.

Thermo doi: 10.3390/thermo4040024

Authors: Pavlos Nikolaidis

Global efforts aiming to shift towards renewable energy and smart grid configurations require accurate unit commitment schedules to guarantee power balance and ensure feasible operation under different complex constraints. Intelligent systems utilizing hybrid and high-level techniques have arisen as promising solutions to provide optimum exploration–exploitation trade-offs at the expense of computational complexity. To ameliorate this requirement, which is extremely expensive in non-interconnected renewable systems, radically different approaches based on enhanced priority schemes and Boolean encoding/decoding have to take place. This compilation encompasses various mappings that convert multi-valued clausal forms into Boolean expressions with equivalent satisfiability. Avoiding any need to introduce prior parameter settings, the solution utilizes state-of-the-art advancements in the field of artificial intelligence models, namely Boolean mapping. It allows for the efficient identification of the optimal configuration of a non-convex system with binary and discontinuous dynamics in the fewest possible trials, providing impressive performance. In this way, Boolean mapping becomes capable of providing global optimum solutions to unit commitment utilizing fully tractable procedures without deteriorating the computational time. The results, considering a non-interconnected power system, show that the proposed model based on artificial intelligence presents advantageous performance in terms of generating cost and complexity. This is particularly important in isolated networks, where even a-not-so great deviation between production and consumption may reflect as a major disturbance in terms of frequency and voltage.

Thermo doi: 10.3390/thermo4040023

Authors: Kaspar M. B. Jansen

Textile heaters are made from knitted conductive yarns integrated into their fabric, making them stretchable, washable, breathable and suitable for close-to-skin wear. However, the non-zero resistance in the lead wires causes non-uniform power distribution, which presents a design challenge. To address this, the electrical performance of the heaters is modeled as an n-ladder resistor network. By using the finite difference method, simple, closed-form expressions are derived for networks with their power source connected to input terminals A1B1 and A1Bn, respectively. The exact results are then used to derive approximations and design criteria. The solutions for the ladder networks presented in this paper apply to a wider class of physical problems, such as irrigation systems, transformer windings, and cooling fins.

Thermo doi: 10.3390/thermo4030022

Authors: Ariel A. Chialvo

This review provides a critical assessment of the current state of affairs regarding the solvation thermodynamics involving mixed-solvent systems. It focuses specifically on (i) its rigorous molecular-based foundations, (ii) the underlying connections between the microstructural behavior of the mixed-solvent environment and its thermodynamic responses, (iii) the microstructural characterization of the behavior of the mixed-solvent environment around the dilute solute via unique fundamental structure-making/-breaking functions and the universal preferential solvation function, (iv) the discussion of potential drawbacks associated with the molecular simulation-based determination of thermodynamic preferential interaction parameters, and (v) the forensic examination of frequent modeling pitfalls behind the interpretation of preferential solvation from experimental data of Gibbs free energy of solute transfer.