Thermo, Volume 6, Issue 3 (September 2026) – 26 articles

High-temperature proton-exchange membrane fuel cells (HT-PEMFCs) generate useful thermal energy that can be recovered for additional power production. This study investigates an integrated HT-PEMFC–organic Rankine cycle (ORC) system by combining response surface methodology (RSM) with thermodynamic energy analysis. A 17-run response-surface design was used to quantify the effects of pressure, temperature, and current density on polarization voltage. Power density was derived directly from the RSM-predicted voltage using P_d = iE to preserve physical consistency. The electrochemical model was benchmarked against published phosphoric-acid-doped polybenzimidazole HT-PEMFC polarization data under comparable conditions. The constrained optimization identified an operating condition of 400 kPa, 443 K, and approximately 1.198 A cm⁻², giving a predicted voltage of 0.5395 V and a power density of approximately 0.6462 W cm⁻². This represents a 12.9% increase in power density relative to the adopted reference condition. Separately, the reference thermodynamic case produced 13.08 kW of gross HT-PEMFC stack electrical power and 15.45 kW of thermal output assumed available to the ORC. The available legacy R409A reference case was evaluated at an evaporator pressure of 2 MPa, yielding approximately 1.24 kW of ORC net power and a net thermal efficiency of about 8.02%. The resulting combined modeled electrical output was approximately 14.32 kW before unmodeled balance-of-plant auxiliary power consumption, with the ORC contribution corresponding to about 9.5% of the gross HT-PEMFC stack output. The results demonstrate the complementary potential of physically consistent HT-PEMFC operating-condition optimization and waste-heat recovery, while the ORC results remain specific to the retained R409A reference dataset. Full article

In this study, the combustion behavior of Çayırhan coal under an oxygen atmosphere was investigated, and its combustion kinetics and thermodynamic parameters were determined. Thermal analyses (TGA, DTG, and DSC) revealed that the combustion process occurs in two consecutive steps. The first step, in which 85% of the total weight loss takes place, requires a relatively low activation energy. Conversely, the second step, corresponding to the remaining 15% of the combustion, requires a significantly higher activation energy. Both combustion steps were analyzed using model-free isoconversional methods. The average activation energies were calculated as 139.65 ± 9.66 kJ/mol for Combustion 1 and 402.27 ± 65.53 kJ/mol for Combustion 2. Subsequent kinetic modeling studies demonstrated that both combustion reactions are highly compatible with the diffusion mechanism. Following the determination of the most suitable reaction model, the Arrhenius pre-exponential factor (A) and other thermodynamic parameters of the activated complex (ΔS^‡, ΔH^‡, and ΔG^‡) were successfully evaluated. These thermodynamic and kinetic insights clarify the distinct combustion regimes of Çayırhan coal under laboratory conditions. Ultimately, the selected diffusion-based kinetic models offer a practical baseline framework for evaluating combustion performance and providing preliminary insights for reactor considerations in low-rank coal applications. Full article

High arch dams are structurally efficient hydraulic structures for demanding loading conditions, including extreme loading, and are widely recognized for the transfer mechanism of such loads acting on them. The distinctive performance of these thin concrete structures during their service life is often intriguing and worth investigating. Unlike in the case of concrete gravity dams, in arch dams—especially, thin arch dams—the impact of temperature loads assumes significance due to the geometry and load-transfer mechanism. In this paper, an existing high double-curvature thin concrete arch dam experiencing fluctuations in reservoir levels is analyzed regarding the combined effect of thermal loads and the deflections and stresses caused. Thermal loads arising from continuous exposure of intrados and extrados faces contribute to critical loading scenarios. The FEM-based simulations assisted with field monitoring data and were used to study the structural response under the influence of temperature in steady-state conditions. The study found that the increase in body temperature is a cause of undesirable tensile stresses in the upper parts of the dam body, close to 2.0 MPa, which may cause the development of horizontal cracks. Small areas of upstream heel portion also develop higher tensile stresses due to temperature loads. The dam in its 50-year service life showed apparently aberrant behavior in deflections. The seasonal temperature variation—an increase—can be a cause of the atypical response of the dam. The anomalous nature of the behavior cannot be considered unusual, but the study also found that mitigation measures are effective, suggesting that continuous monitoring is required for sustained healthy functioning. Full article

This study integrates a Radial Basis Function Neural Network (RBFNN) with Adaptive Dynamic Programming (ADP) to develop an Action-Dependent Heuristic Dynamic Programming (ADHDP) framework for the cost-effective control of an Ice Storage Air-Conditioning (IAC) system. The proposed approach aims to establish a self-learning control strategy for reducing the overall operating cost of the system. In this study, the operational states of the air-conditioning system and the ice-storage/release states of the ice-storage tank are selected as the control variables. To approximate the nonlinear cost-to-go function of the IAC scheduling problem, an RBFNN is employed as the critic-network function approximator. Its local nonlinear approximation capability enables the controller to evaluate the long-term operating costs associated with different ice-storage, ice-melting, and air-conditioning actions. As a result, the proposed ADHDP method can evaluate feasible operating actions and select the action associated with the minimum estimated cost-to-go. Furthermore, an actual IAC system is adopted as the research subject. Field operational data are collected and utilized for system modeling and analysis. Simulations are conducted to compare the Conventional Control Strategy (CCS), ADP, and the ADHDP approach, with operating cost serving as the primary evaluation index. For the investigated representative operating scenario, ADHDP achieved operating costs approximately 7.24% and 1.66% lower than CCS and ADP, respectively. These values represent case-study results under the specific operating conditions considered in this study. Moreover, the ADHDP framework exhibits stronger adaptability to varying cooling loads and electricity pricing conditions, thereby improving the operational efficiency and energy management capability of the IAC system. Full article

Buildings account for roughly 37% of energy-related CO₂ emissions, and space cooling already consumes nearly 10% of global electricity. Cooling demand is rising fastest in tropical cities, where air-conditioning could reach 45% of peak load, especially in India by 2050. This review critically examines thermal energy storage (TES) as a flexibility resource across three distinct scales: individual buildings, district heating and cooling networks, and city-level multi-energy systems. Using a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-based search of Scopus, Web of Science, and IEEE Xplore with primary and supplementary strings, 4447 records were identified, of which 174 were included. Each quantitative study was classified by validation level (simulation, laboratory, pilot, or operational) and by the centrality of thermal storage. Sensible, latent, and thermochemical storage technologies are compared using energy density (10–500 kWh/m³), efficiency (40–95%), cycle stability, and technology readiness. The review then evaluates the role of artificial intelligence (AI), machine learning, and Internet of Things platforms in forecasting, predictive control, and operational optimization of TES networks. Thirteen method families, grouped into AI and machine learning methods, optimization methods, control methods, and digital enabling technologies, are assessed against six explicitly defined criteria with evidence-coded scores. Among 47 quantitative studies, 37 (78.7%) are simulation-only, and only four (8.5%) report operational data. Direct TES-AI studies report simulated energy savings of 8–64% and peak load reductions of about 35%, whereas field-validated intelligent control reports 17% energy savings in a single real building experiment. The review also identifies inherent drawbacks of artificial intelligence-based operations, including limited interpretability, high data and computational demands, concept drift, and cyber vulnerabilities that increased peak electric load by 17.4% in a simulated attack. A structural imbalance in the literature is evident: most validated deployments remain at the building-scale, whereas urban-scale evidence is confined to district cooling, aquifer and pit storage, and multi-energy hub studies; no study reports the coordinated operation of distributed TES assets across multiple districts. A conceptual framework and a staged roadmap linking building, district, and urban scales are proposed. Priority research needs include urban-scale pilots in tropical climates, techno-economic assessment, interpretable and drift-robust AI, and interoperability standards that support United Nations’ Sustainable Development Goals 7, 11, and 13. Full article

Extremely fast charging (XFC) of high-energy-density lithium-ion batteries is fundamentally constrained by the intrinsic waveform characteristics of conventional variable-current profiles (VCPs), limiting further reductions in charging time while maintaining electro-thermal safety. In the present study, a computational electro-thermally constrained optimization framework is developed in which a square-wave VCP is reformulated using a finite Fourier series to improve XFC performance. An electro-thermal numerical model is employed to evaluate the charging behavior of the resulting Fourier series-based square wave (F-square wave) with the number of harmonic terms ranging from N = 1 to 100. The optimal charging performance is achieved at N = 10, reducing the charging time from 940 to 878 s (6.6%) and satisfying the U.S. DOE 15-min XFC target (900 s). The performance enhancement originates from two complementary effects: the Gibbs overshoot, which locally increases the charging current near the allowable current limit, and the finite-series approximation, which smooths the current transition before and after the waveform discontinuity. Rather than treating the Gibbs overshoot associated with Fourier approximation as an undesirable numerical artifact, this study demonstrates that it can be computationally exploited as a controlled perturbation to accelerate charging while maintaining electro-thermal safety. Although the Fourier perturbation slightly increases the terminal voltage risk near the waveform discontinuity, all electrical and thermal constraints remain satisfied throughout the charging process. These findings demonstrate that finite Fourier perturbation provides an effective computational design strategy for overcoming the intrinsic waveform limitations of discontinuous charging profiles and advancing electro-thermally constrained XFC of lithium-ion batteries. Full article

Uncertainty propagation and transient heat transfer for a hollow sphere are analyzed. The stochastic Biot number, stochastic linear non-dimensional initial conditions, and various boundary conditions are introduced to define uncertainty propagation influencing the temperature distribution throughout the hollow sphere. The resulting uncertainty amplitude was observed to have transient evolution in time. The uncertainty can either increase or decrease depending on the stochastic parameters. Results are presented for the variation in temperature due to uncertainties in the initial conditions and particular boundary conditions. Full article

To comply with stringent emission regulations, the deployment of hybridized powertrains is continuously expanding. However, architectures such as plug-in and parallel hybrids intrinsically reduce the overall runtime of the internal combustion engine (ICE). Because the battery state-of-charge (SOC) dictates intermittent engine activation, this operational strategy inevitably induces frequent cold-start events. This study investigates the thermal dynamics of commercial catalyst geometries (300–1200 cpsi, 2–8 mil) via 1D numerical simulations under real-world driving conditions. Without active heating, high-thermal-mass substrates unexpectedly outperform ultra-thin-wall variants by buffering against convective quenching during prolonged idling. However, integrating start–stop functionality halts cold exhaust flow, elevating mean temperatures and marginalizing geometric disparities. Evaluating electrically heated catalysts (EHCs) reveals that discrete preheating is highly inefficient due to rapid heat dissipation. Conversely, continuous closed-loop heating coupled with start–stop functionality sustains operational temperatures for over 90% of the cycle. Under continuous heating, substrate geometry ceases to dictate thermal performance; instead, it governs electrical efficiency. Low-thermal-mass monoliths minimize cumulative energy demand to 213 kJ (versus 277 kJ for high-mass variants), incurring a negligible CO₂ penalty. Consequently, future hybrid architectures must integrate lightweight EHCs to ensure sustainable emission control. Full article

In this work, the effect of mechanical activation (MA) on the double complex salt (DCS) [Co(NH₃)₆][Fe(C₂O₄)₃]·3H₂O and its thermolysis is investigated. Mechanical activation is a promising “green chemistry” method that allows improving the physicochemical properties of the DCS [Co(NH₃)₆][Fe(C₂O₄)₃]·3H₂O and the products of its thermal decomposition in an argon atmosphere. The conditions of the MA process and the effect of MA and passivation on the process and kinetics of DCS thermal degradation were investigated. It was shown that due to the removal of outer-sphere coordinated water and carbonation of the DCS during MA, the number of thermal degradation stages changes. It was established that passivation at 450 °C for MA times of 0 and 10 min prevents spontaneous “combustion” of the thermal degradation products of the DCS. Optimal conditions for DCS processing were determined to be 5 min of MA and heat treatment at 450 °C without passivation. Under these conditions, the yield of the CoFe intermetallic compound reaches 82.6 wt%. This optimal combination of sample production conditions allows for a reduction in MA time and the elimination of the passivation process, making the process more cost-effective and creating conditions for optimizing the production of functional materials. Full article

Pyrolysis is a leading route for valorizing lignocellulosic residues, yet detailed multi-step kinetic schemes have so far been deployed only in costly commercial simulators, limiting reproducibility. This work couples thermogravimetric (TGA) characterization with process simulation in the free, open-source simulator DWSIM to predict the pyrolysis product distribution of corn cob from Córdoba, Colombia. The lignocellulosic composition (hemicellulose 24.3 ± 2.9, cellulose 36.4 ± 3.0, lignin 39.3 ± 0.9 wt%) was obtained by deconvolving the derivative thermogravimetric (DTG) curve with a five-parameter asymmetric double sigmoidal (Asym2sig) function (R² > 0.9996). Pseudocomponent activation energies from the Coats–Redfern method (154.2, 124.6, and 29.9 kJ/mol) calibrated the primary reactions of a 17-reaction Ranzi scheme, extended with 18 secondary gas-phase steam reforming reactions. Validated against eight lignocellulosic biomasses, the calibrated model yielded a consolidated R² = 0.853 and average absolute deviation (AAD) = 9.8%, with char predictions most accurate (AAD = 8.9%). For corn cob, a bio-oil-optimized yield of 55.0 wt% was predicted at 500 °C, transitioning to a syngas-rich regime (51.0 wt% gas) at 750 °C. This constitutes the calibrated Ranzi-scheme implementation in DWSIM, offering an accessible, reproducible pathway for biomass pyrolysis modeling. Full article

This study presents a transient two-dimensional model devised to predict frost build-up, pressure drop, and sensible and latent heat transfer rates in tube-fin evaporators, commonly used in ‘frost-free’ refrigerators. Based on the first principles of mass, momentum, and energy conservation for the airflow and the frost layer, the model accurately simulates evaporator blockage over time. Furthermore, it incorporates the interaction between the heat exchanger air-side impedance and the fan performance characteristic curve, using an iterative fluid-dynamic sub-model that predicts airflow reduction and redistribution in an evaporator with three fin densities. Frost accretion experiments were conducted using a purpose-built test setup consisting of a bottom-mount refrigerator cabinet maintained at controlled temperature and humidity in both the fresh and frozen-food compartments. Model validation demonstrated that the predicted results closely matched experimental observations. The results show that localized frost accumulation at fin density transitions causes severe airflow blockage, resulting in a 75% reduction in effective heat transfer area due to uneven air distribution. Finally, an analysis of two dimensionless competing indices demonstrates that fin density selection involves a critical trade-off between the initial cooling capacity and long-term frost resilience. Full article

Accurate prediction of coupled heat-transfer and fluid-flow phenomena is essential for the thermal design, performance assessment, and optimization of heat exchangers (HXs). Among key HXs, concentric tube heat exchangers (CTHXs) are widely used in thermal energy systems, where their performance is governed by the coupled interaction of fluid flow and heat transfer. Although computational fluid dynamics (CFD) provides detailed insights into these transport phenomena, its high computational cost limits its applicability in design optimization and real-time monitoring applications. To overcome this limitation, the present study proposes a physics-guided neural network (PGNN) for the accurate and efficient prediction of CTHX thermo-hydraulic performance, including the overall heat-transfer coefficient (U) and the pressure drops of the cold (ΔP_c) and hot (ΔP_h) streams. The PGNN introduces correlation-based physical guidance through established Nusselt number, overall thermal-resistance, and Darcy–Weisbach pressure-drop relations. Accordingly, the proposed framework is a correlation-guided PGNN rather than a residual-based physics-informed model, because the local conservation-equation residuals are not explicitly enforced during training. For comparison, a standard artificial neural network (ANN) with the same architecture and input parameters was also developed. Both models were trained on a dataset generated from 1575 CFD simulations covering a wide range of operating and geometric conditions, including the Reynolds and Prandtl numbers of both fluids, inner and outer tube diameters, and inlet temperatures. A comprehensive error analysis demonstrates the superior predictive capability of the PGNN over the ANN under various flow and geometric conditions. On the unseen test dataset, the PGNN achieved mean absolute percentage errors of 2.03%, 1.09%, and 1.11% for predicting U, ΔP_c, and ΔP_h, respectively. The proposed PGNN therefore provides a reliable, high-fidelity, and computationally efficient alternative to CFD, supporting the analysis, optimization, and operation of thermal energy systems. Full article

This study addresses the energy demand profiles of commercial buildings by developing an optimal dispatch strategy for a regional high-efficiency distributed energy system integrating electricity, cooling, and storage through source–load coordination. The spatiotemporal distribution characteristics of cooling, heating, and electrical loads are analyzed and an integrated energy system model is established, comprising gas internal combustion engine, a lithium bromide absorption chiller/heater, gas-fired boiler, centrifugal chillers, and an ice storage system. Taking into account seasonal electricity pricing policies and meteorological variations in Shanghai, a load grading system and a time-of-use (TOU) pricing response mechanism are constructed, leading to the development of operational strategy portfolios for different typical scenarios. A multi-objective optimization dispatch model is formulated with the dual aims of minimizing operating costs and maximizing energy efficiency. The results indicate that, compared to a fixed operational mode, the optimized strategy achieves average CO₂ emission reduction rates of 16.4% in summer, 25.2% in non-summer periods, and 20.9% annually. Additionally, annual grid electricity purchases are reduced by 10.2%, with a static investment payback period of 11.37 years. This research provides an intelligent, practically applicable operational solution for distributed energy systems in commercial buildings, effectively overcoming the limitations of traditional approaches in terms of flexibility and economic performance. Full article

Ventilated façades are increasingly used in building renovations, often containing non-renewable and CO₂-emissions-intensive cement-based materials. Renewable biomass-based materials offer a more sustainable alternative with a high amount of sequestered CO₂. However, water uptake is a critical factor in exterior applications. This study investigates the water resistance of high-density particleboards made of wheat straw (WS), grey alder (GA), and softwood (SW) for façade-related exterior applications. Two general board types were produced from each biomass using (1) steam explosion (SE) treatment and (2) the addition of birch-bark-derived suberinic acids (SAs) as the bio-based binder. In addition, the influence of conventional and mold hot pressing was investigated. The particleboards were coated with four types of innovative finishes, comprising (1) purified SA, (2) SA + chitosan (SH), (3) SA + earth pigment (SP), and (4) SHP. The water resistance of the particleboards was evaluated using an internal bonding (IB) test after 2 h of boiling and by measuring the water drop contact angle. FTIR analysis was performed to identify differences between the board varieties and to explain the obtained results. Only two board varieties (GASA and SWSA) fulfilled the Type P5 EN 312 water resistance requirement (0.15 N/mm²), achieving IB values of 0.81 ± 0.23 N/mm² and 0.22 ± 0.07 N/mm², respectively. In turn, the coatings used did not significantly increase the static contact angle compared to the reference board. Although the results of this study confirm the inherent moisture sensitivity of engineered particleboards, two board varieties demonstrate promising potential for façade-related exterior applications. Full article

Decarbonizing industrial heating in cold climates remains challenging due to high thermal demand and strong seasonal variability. While the existing literature predominantly relies on steady-state or isolated component analyses, this study introduces a novel, multi-scale dynamic modeling framework. This framework evaluates the annual transient performance of an integrated renewable architecture. The proposed system couples a building-envelope Transpired Solar Collector (TSC) with a series-connected Photovoltaic Thermal/Solar Thermal (PVT-ST) array. Computational Fluid Dynamics (CFD) is employed to resolve the localized convective heat transfer within the TSC. Subsequently, a data-driven clustering methodology scales these transient results into a comprehensive annual system-level simulation featuring sensible Thermal Energy Storage (TES). The results demonstrate robust performance under Canadian winter conditions. The TSC maintains stable thermal efficiencies between 50% and 60%, peaking at over 64%. Annually, the integrated dual-source system delivers 229.7 MWh of useful thermal energy to offset primary fossil fuel consumption. Furthermore, the analysis identifies 128.76 MWh of seasonal surplus capacity. This underscores the critical necessity of dynamic TES integration. Ultimately, this framework establishes a highly defensible, predictive methodology for designing and implementing synergistic solar thermal networks for industrial decarbonization. Full article

Conventional continuum thermodynamics is characterized by a classical form of the energy law and the second law of thermodynamics in the form of the Clausius–Duhem inequality. This thermodynamic framework fails to capture certain features in material response as, e.g., length scale effects, temperature waves in rigid heat conductors and diffusion phenomena. Typically, such material characteristics are associated with pronounced non-localities in time and space. To tackle these issues, non-conventional thermodynamic approaches might be appropriate. The employment of non-conventional thermodynamics is very attractive, as it enables the extension of the applicability of conventional thermodynamics in a simple way. A specific non-conventional thermodynamic framework has previously been proposed as a generalization of irreversible thermodynamics. Energy supply effects were neglected in this work. However, energy supply terms may become important when discussing thermodynamical consistency of many physical models. The present paper extends the applicability of the proposed non-conventional thermodynamic framework by accounting for energy supply densities and demonstrates its capabilities by addressing Cattaneo’s heat conduction law—known for predicting temperature waves—and thermo-diffusion coupling theories. It is shown that, within the adopted thermodynamics, the considered physical models are thermodynamically consistent and that the resulting field theories admit formulations within a variational framework for rate problems; in this sense, the models are properly formulated. Full article

Tables giving gas properties at low pressure enable the efficient analysis of processes in which the gas is approximated as thermally perfect but not calorically perfect. In addition to specific enthalpy and specific internal energy, thermally perfect gas tables include special functions that depend only on temperature—relative pressure and relative specific volume. These functions may be used to determine pressure, volume, and temperature of thermally perfect gases undergoing hypothetical isentropic processes. However, the definitions of these functions included in widely used thermodynamics textbooks are vague, inconsistent, or incorrect. The intent of this work is to discuss common inaccuracies in the definitions and the tabulated values of relative pressure and relative specific volume. The origins of the tabulated data used in many engineering thermodynamics textbooks are reviewed and consistent definitions are proposed. A table listing thermally perfect gas properties for air at low pressure based on the proposed definitions is presented. Full article

Thermal energy storage plays a crucial role in meeting human energy demands and is particularly essential for many solar energy applications. Among the various storage methods, phase change materials (PCMs) have attracted significant attention because their thermal performance can be greatly influenced by the material properties, physical characteristics, and the geometry of the encapsulating container. In this paper, the melting process of phase change materials (PCMs) within an elliptical enclosure using the finite volume method is analyzed. Gallium is selected as a PCM with a low Prandtl number. A physical model employing the enthalpy porosity formulation is elaborated to describe the coupling between natural convection and the melting process of PCMs. Numerical simulations are performed to examine the influence of the aspect ratio (n = b/a), ranging from 1 to 4, and inclination angles from 0° to 90° of the elliptical enclosure on the melting process. It has been found that the use of the elliptical capsule can reduce the melting process time. For a Rayleigh number of ${10}^6$, the melting time decreases as the aspect ratio increases from 1 (circle) to 4. The horizontal orientation (θ = 0°) is found to be the most efficient, with a melting rate higher than that observed for inclined positions (30°, 45°, 60°, and 90°). For a low Rayleigh number of ${10}^4$, the inclination angle has an imperceptible effect on the phase change. Empirical correlations are proposed to relate the Nusselt number to the Rayleigh number, with coefficients adapted to different Fourier numbers and geometric parameters. Full article

The increasing penetration of variable renewable energy sources (RESs) poses significant challenges to power system flexibility and reliability, particularly in systems with high solar generation. At the same time, existing Concentrating Solar Power (CSP) plants in Europe face declining economic viability due to high capital costs and the expiration of incentivized tariff schemes. This study proposes and evaluates a novel approach to repurpose CSP plants as flexible energy assets through the integration of cold thermal energy storage (CTES) within a Thermally Integrated Power-to-Heat-to-Power Energy Storage (TI-PTES) framework. The proposed system combines an ice/water-based cold storage with a CO₂-based refrigeration cycle to enhance the efficiency of the CSP steam cycle by reducing condenser temperatures, while also enabling temporal shifting of electricity consumption. A techno-economic optimization model based on PyPSA is developed to determine the optimal sizing and operation of the storage and refrigeration system under realistic load and electricity price conditions representative of the Spanish market. Results show that the integration of cold storage significantly alters system operation, shifting the chiller from a continuous demand-following mode to an intermittent, high-intensity regime. This leads to a reduction in annual operating expenditures by approximately 32% and an increase in annual profit and net present value (NPV), despite higher capital investment. While hourly net revenue becomes more volatile, with negative values during charging periods, cumulative annual performance improves due to effective temporal optimization. However, the absence of strong electricity price arbitrage and negative price signals limits the revenue potential of the storage system, which primarily acts as a cost-reduction mechanism. The findings demonstrate that cold thermal storage can successfully reposition CSP plants as flexible, value-generating assets in modern electricity systems. The proposed concept offers a promising pathway for extending the operational lifetime of existing CSP infrastructure while supporting higher integration of renewable energy sources. Full article

This numerical study investigates the thermo-hydraulic and thermodynamic performance of a rectangular-channel heat exchanger incorporating isothermal circular tubes, with particular emphasis on geometric design strategies suitable for compact thermal systems. Two configurations with identical total heat transfer surfaces are analyzed: baseline geometry comprising four aligned tubes (G1) and an optimized geometry consisting of eight tubes arranged in two parallel rows (G2) maintaining the same exchange surface. Laminar forced convection is also considered. For the baseline configuration, results show a pronounced thermal shadowing effect, leading to a reduction of nearly 50% in the heat transfer contribution of downstream tubes.In contrast, optimized geometry significantly improves flow redistribution and temperature field uniformity. An optimal inter-row spacing, equal to 0.1, is identified as a robust design parameter, maximizing the total average Nusselt number. At this spacing, all heated surfaces actively contribute to heat transfer, resulting on an overall heat transfer enhancement of approximately 20–40% compared to the baseline configuration. Entropy production analysis shows that increasing Re strongly intensifies thermal irreversibility, while viscous irreversibility exhibits a moderate increase. The impact of nanoparticles addition, carried out on the optimal configuration of G2, shows that heat transfer increases by about 8% for a nanoparticle concentration of 4% at high Re values, with an insignificant change in the Bejan number. The present findings demonstrate that geometric optimization represents a more effective and energetically sustainable enhancement strategy than nanofluid addition for compact tubular heat exchangers. Full article

Additive Manufacturing (AM) for jewelry applications is increasingly adopting Binder Jetting (BJ) to overcome the fusion-related limitations associated with precious metals, including unstable melt pools, excessive reflectivity, and high thermal conductivity. In this context, the present review establishes a thermophysical and manufacturability-oriented framework that redefines thermal management beyond localized melt-pool stabilization toward the furnace-scale control of densification kinetics, shrinkage evolution, atmosphere-assisted sintering, and viscoplastic deformation. Particular emphasis is placed on gold-, silver-, and platinum-based jewelry alloys, with a specific focus on the thermal, mechanical, and chemical phenomena governing Binder Jetting sintering. During consolidation, low-density green bodies (~40–65% relative density) must transform into highly dense components through extensive volumetric shrinkage and gravity-driven deformation, creating major challenges in dimensional fidelity and surface quality. The review further examines predictive viscoplastic constitutive models (SOVS/ROH), reversed-deformation compensation strategies, and atmosphere-engineering approaches for oxide reduction, pore-pressure regulation, and residual-porosity control. By linking thermophysical consolidation, dimensional fidelity, polishability, and jewelry-grade manufacturability within a hierarchical framework, this review provides a structured basis for the development of high-precision and low-waste precious-metal additive manufacturing. Full article

This experimental study investigates the performance and sustainability of a modified double-slope solar still (MDSSS) integrated with a combined water channel to enhance evaporation rates. The integration of the water channel ensures uniform water flow and enhanced heat distribution across the basin surface, thereby improving thermal performance. Experiments were conducted using three types of feed water, groundwater, saline water, and domestic wastewater, to assess the system’s versatility and effectiveness in various water desalination applications. Under identical meteorological conditions, thermal parameters, distillate yield, energy efficiency, and sustainability were analyzed. The results revealed that incorporating the water channel significantly increased evaporation and condensation rates compared to the conventional double-slope solar still (DSSS) configuration. Also, the performance of an MDSSS was evaluated under various water qualities, including physical, chemical, and biological parameters. The experiment begins at half the optimal water depth for water quality, with the remaining half passing through an open-channel attachment into the solar still basin. The modified system effectively reduced pollutants, achieving a 98.18% reduction in chemical oxygen demand in groundwater, complete salt removal from saline water, and a 96.67% reduction in sewage water. Full article

This study investigated the thermophysical properties of mangaba (Hancornia speciosa) and guavira (Campomanesia adamantium) pulps at different soluble solid concentrations (9.0 to 13.5 °Brix) and temperatures (0 to −25 °C). Using mathematical models and experimental data, properties such as density (ρ), apparent specific heat capacity (c_p), thermal conductivity (k), and thermal diffusivity (α) were estimated. The results showed that all properties were strongly influenced by temperature and concentration. Density and apparent specific heat capacity increased with °Brix and temperature, while thermal conductivity and diffusivity were higher in samples with greater moisture content. These results provide useful information for the design, simulation, and optimization of freezing and storage processes for native Cerrado fruit pulps, contributing to their technological valorization and potential use in frozen food products. Full article

An experimental setup has been developed that enables the conversion of a complex stream of polydisperse droplets generated by an ultrasonic dispenser into a stream of nearly identical droplets falling through a vertical channel. The fall of droplets of an aqueous NaCl solution in this channel, filled with heated dry air, is studied. Water from the droplets evaporates quickly, and crystals of a solid salt crust form on their surface. At a later stage of the process, the remaining solution is removed from the droplet using a jet of water vapor that passes through the pores of the polycrystalline crust. It was first observed that some of the drying droplets suddenly shifted to one side under the influence of the reactive force generated by the vapor jet. Images obtained using a scanning electron microscope show that the salt particles formed have a diameter of around 25 µm, are slightly porous, and consist of numerous crystals. It has been proven that these particles do not have a central cavity. The use of seawater and the role of salt particles in protecting against thermal radiation from fires are briefly discussed. Calculations based on Mie theory have shown that the contribution of light scattering by thin-walled hollow sea salt particles formed above the ocean surface during relatively slow evaporation of seawater droplets can be significant to the ocean’s heat balance. Full article

The present paper is motivated by challenges in the design of the surface insulation in borehole thermal energy storage (BTES). A case study of a BTES with nine borehole heat exchangers (BHEs) in a cold climate is considered. Transient numerical modeling of the storage charging phase is performed by solving the three-dimensional heat equation using the finite difference method. Heat conduction through the insulation cover is simulated in accordance with Fourier’s law. A parametric study is conducted with respect to the prescribed heating setpoint temperatures in the BHEs and to the geometry of the insulation cover. The thermal analysis shows that the efficiency of the storage volume is strongly dependent on the heat transfer through the upper boundary. The insulation layer affects the minimum temperature reached within the BTES, with the influence of insulation thickness being most pronounced at thicknesses up to 10 cm. Furthermore, it is demonstrated that the lateral extension of the insulation cover has a greater impact on storage capacity gains than increasing its thickness, and that these energy gains expand progressively over time. Under cold ambient conditions, effective seasonal storage requires managing sharp ambient thermal gradients via a wider peripheral coverage of the insulation layer to offset vertical conductive losses. Full article