Thermo, Volume 6, Issue 2 (June 2026) – 12 articles

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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 ($u=0.70$, $L=5 \mathrm{k}$m) 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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article