Search Results (2,338)

This study systematically investigated flow boiling characteristics within a novel three-layer microchannel heat sink with 3/4 open-ring pin fin arrays, designed for high-heat-flux thermal management of low-carbon metallurgical reactors. Two-phase flow regimes, pressure drop, and wall temperature responses were analyzed. To evaluate the impact of functional surface material properties on thermo-hydraulic behavior, a hydrophilic nano-coating modification was applied to the inner copper channel walls for comparison. Increasing the flow rate triggered a transition from a vapor-dominated confined slug flow to a liquid-dominated dispersed bubble flow, which effectively improved the thermo-hydraulic stability. Hydrophilic surface modification resulted in an average pressure drop reduction of 33% and significantly diminished the sensitivity of flow resistance to velocity variations. Through hydrophilic treatment, the localized vapor film effect at high velocities was suppressed, and temperature field homogenization was promoted, yielding a maximum convective heat transfer coefficient of 7760 W/(m²·°C), i.e., 72.9% enhancement over the baseline heat sink. The underlying mechanism is attributed to the formation of a stable near-wall thin liquid film and the promotion of high-frequency nucleate boiling. These results will be of high relevance for developing efficient cooling solutions for power electronics, thereby supporting the advancement of low-carbon metallurgical reactors. Full article

Integrating a heat exchanger (HEX) into the cooling duct of a high-power fuel-cell-based aircraft presents a critical trade-off between thermal performance and aerodynamic penalties. The present study addresses this challenge through the design and system-level analysis of a HEX integrated into the cooling duct. Developed as part of the Clean Aviation project FAME, the design features a rectangular inlet, a circular outlet, and a tilted HEX. The evaluation is performed using high-fidelity Large Eddy Simulations (LESs). The HEX is modeled with a porous media approach based on the Darcy–Forchheimer equation, while the simulations are carried out using a self-adapted version of the pisoFoam solver, termed pisoTempFoam, to account for heat transfer. The study reveals that while component-level design choices, such as a straight inlet and tilted HEX configuration, successfully mitigate local flow separation and duct-induced losses, a critical system-level performance issue emerges. The analysis demonstrates that the cooling duct design, when subjected to realistic operational conditions, generates the high pressure head to overcome the resistance of the HEX. The external aerodynamic analysis also indicates that the HEX resistance is a critical factor, and without overcoming it the system fails to capture the required air mass flow rate, compromising thermal management. The findings highlight the necessity to optimize the design, by an adapted duct shape or an auxiliary fan, to overcome the HEX-induced pressure drop. The porous media approach is thereby validated as an effective tool for rapid system-level design analysis, despite its inherent limitation in capturing detailed downstream turbulence. Full article

This study presents a controlled three-dimensional conjugate CFD comparison of counter-flow and parallel-flow concentric tube heat exchangers under identical Reynolds number conditions (Re = 1000–2000). By isolating the flow configuration as the only varying parameter, the intrinsic influence of flow arrangement on thermo-hydraulic performance is systematically evaluated. Unlike enhancement-focused studies involving geometric modification or advanced working fluids, the present study focuses exclusively on the influence of flow arrangement under identical operating conditions. The analysis focuses on heat transfer rate, outlet temperature distribution, pressure drop, thermo-hydraulic performance index, and a normalized heat transfer ratio (Ψ). The results show that the counter-flow configuration consistently enhances heat transfer by 3.17–4.29% compared to parallel-flow operation, while maintaining nearly identical pressure-drop values. This improvement is attributed to the preservation of a higher logarithmic mean temperature difference (LMTD) along the exchanger length, sustaining the thermal driving force under laminar flow conditions. In contrast, the parallel-flow configuration exhibits a rapid decay in temperature difference near the inlet region, limiting effective heat transfer. Although heat transfer increases with Reynolds number in both configurations, the thermo-hydraulic performance index decreases due to the relatively higher increase in hydraulic resistance. Comparison with classical laminar flow behavior confirmed the physical consistency and reliability of the numerical model. The findings demonstrate that counter-flow arrangement provides a measurable thermal advantage without additional hydraulic penalty. The study offers a physically consistent and practically relevant framework for the design and optimization of concentric tube heat exchangers used in engine cooling and waste heat recovery applications. Full article

Following a loss-of-coolant accident, the reactor safety injection system is activated, and a large amount of coolant is injected into the reactor pressure vessel (RPV). This induces cold plume phenomena and temperature nonuniformity inside the vessel, which may threaten the structural integrity of the RPV. Transient numerical simulations are performed to investigate the complex cold plumes that arise inside the pressure vessel of a small mobile reactor under safety-injection conditions. By evaluating the flow-field evolution under different injection paths and flow rates, and by innovatively adapting classical plume entrainment theory to define an equivalent coefficient for the nuclear engineering context, this study systematically analyzes the formation and development of the cold plumes and their entrainment–mixing mechanisms. The results indicate that, in such compact RPVs, the entrainment and mixing intensity of the cold plumes is relatively weak, resulting in ineffective thermal mixing during the development stage. Although increasing the injection flow rate enhances heat transfer and reduces thermal gradients, the improvement exhibits diminishing returns. A comparison of different injection paths reveals that a dual-line injection scheme leverages plume–plume interaction to effectively strengthen radial mixing, accelerate temperature-field homogenization, and enlarge the wall-cooling region, thereby alleviating local pressurized thermal shock (PTS). Full article

The fuel and operation efficiency of combustion engines and power plants as a whole depends essentially on the in-cycle air temperature and drops when the temperature increases. Thermally stabilized, fuel-efficient engine operation at lower air temperatures is possible due to cooling. This can be conducted by heat recovery chillers (HRC) consuming the heat removed from the engine. Such combined production of power, heat, and refrigeration, applied for cooling engine in-cycle air, is considered to be a promising trend in integrated energy systems (IES) and energetics as a whole. The in-cycle trigeneration ensures a sustainable, thermally stabilized, and highly fuel-efficient operation of power plants. Starting from the strong influence of cyclic air temperature, the rate of in-cycle air cooling is considered as the rate of engine thermal stabilization (RS) and calculated as a ratio of the real drop in cyclic air temperatures to their target values when cooling air to the desired temperatures. Such a novel approach allows for assessing the effectiveness of cooling air issuing based on both aspects: fuel efficiency and engine thermal stabilization quantitatively by RS as a unified primary criterion indicator to synthesize a cooling system with heightened RS. A case study of an IES with in-cycle trigeneration confirmed that the developed an innovative gas engine cyclic air cooling system provided increased annual average weighted values of RS_avr of about 0.44 with an enlarged duration of engine thermally stabilized operation against 0.24 for a basic typical system. Furthermore, the engine’s thermally stabilized operation due to in-cycle air cooling ensures minimum thermal load fluctuations, caused by air temperature variation. As a result, the concept of sustainable fuel-efficient operation of IES due to in-cycle air cooling and the general approaches, hypotheses, and criteria at its core have been developed. Full article

Carbon nanotube yarn (CNTY) monofilament composites were investigated for integrated temperature sensing by embedding a single CNTY in a vinyl ester resin (VER) and measuring the electrical resistance change by tapping into the thermoresistive response of the CNTY. The effect of curing condition on the thermoresistive response was evaluated using dwell tests and repeated heating–cooling cycles, comparing specimens cured at room temperature (RT) with those post-cured at 140 °C for 1 h. RT-cured CNTY/VER monofilament composites exhibited electrical resistance drift, with the resistance failing to return to its initial value after each thermal cycle, resulting in a residual resistance change of ~8.85%. In contrast, post-cured (PC) specimens showed a much smaller residual change (−0.08%) after cycle completion. Thermal cycling from RT (~25 °C) to 100 °C produced a nearly linear negative thermoresistive response. The average heating and cooling TCR values were −7.98 × 10⁻⁴ °C⁻¹ and −8.32 × 10⁻⁴ °C⁻¹ for CNTY/VER, and −7.93 × 10⁻⁴ °C⁻¹ and −7.13 × 10⁻⁴ °C⁻¹ for CNTY/VER-PC, respectively. The hysteresis decreased from 21.65% for RT-cured specimens to 12.49% after post-curing, accompanied by improved linearity. The influence of heating rate on TCR was also examined for both freestanding CNTYs and CNTY/VER monofilament composites. The observed response is attributed to coupled matrix–yarn effects (wetting, resin infiltration, and shrinkage) together with temperature-dependent electron transport across CNT junctions. Finally, CNTY/VER monofilament composites demonstrated the ability to estimate internal temperatures under various thermal programs. Full article

Soft operational faults can noticeably degrade the performance of heat pumps and influence key monitored variables, emphasizing the need for reliable Fault Detection, Diagnosis, and Evaluation (FDDE) strategies. The BEYOND project tackles this challenge by analyzing simultaneous soft faults using a calibrated simulation model informed by data from a dedicated test rig. Achieving reliable results depends on both accurate measurements and proper model calibration. However, sensor uncertainty and errors in sub-models and correlations calibration can compromise model reliability. This work investigates the influence of measurement accuracy and calibration quality on both experimental variables and simulation outcomes for a residential air-to-water heat pump operating in cooling mode, with particular focus on refrigerant charge estimation. Two sensor configurations—“low accuracy” and “high accuracy”—are assessed, representing commercial- and laboratory-grade instruments, respectively, along with two corresponding calibration strategies. In the low-accuracy case, uncertainties around 10% were found for cooling capacity, energy efficiency ratio, and refrigerant mass flow rate, whereas high-accuracy setups reduced these to approximately 3%. Ultimately, the comparison between experimental and model-derived uncertainties confirms that achieving reliable predictions requires a balanced investment in both high-quality instrumentation and careful model calibration. Overall, this study serves as a crucial tool during the preliminary design of an experimental setup, assisting in the selection of a sensor suite that ensures not only the reliability of secondary variables and KPIs but also a robust and accurate calibration of physics-based models using the acquired experimental data. Full article

This paper develops a novel coupled model to predict the thermal behavior of a high-temperature fast heat storage unit, integrating Power-to-Heat technology with steam generation. A phase change material (PCM) made of a ZnAl₆ metal alloy is used for heat storage. Electricity is used to charge the battery, and the stored energy is used to produce superheated steam during discharge. The coupled model was based on a 3D multiphase CFD model of the heat storage unit and a 1D multiphase water boiling model implemented in Python language. The CFD model solves the transient conservation equations of mass, momentum, and energy using the enthalpy–porosity method to describe phase change, while heat transfer to water is represented by a coupled 1D boiling model. The paper also presents a preliminary design, a computational strategy, and boundary conditions for the operating modes, providing an analytical foundation for detailed engineering, production, and implementation in real-world industrial environments. The presented results confirmed the correct operation of the model and enabled the evaluation of system performance, discharge behavior, and validation of the geometric assumptions required to achieve the target steam parameters. The proposed modular design allows for system scalability, while the entire system is a response to the daily variability of electricity prices resulting from periodic reductions in demand and overproduction of electricity from renewable sources. Estimated thermal behavior of the thermal storage unit for the discharging scenario allows reaching constant output power at the level of 200 kW for 85 min. Integration with a cooling reduction station allows constant system power output to be maintained by increasing the mass flow rate as the steam parameters decrease from over 400 °C to 200 °C with a lowering state of charge. Full article

Decarbonizing HVAC in hot–arid regions is challenging for natatoriums because year-round cooling must be delivered alongside stringent dehumidification and occasional heating under high ambient temperatures. In this paper, a fully renewable system has been developed and evaluated for an indoor swimming pool located in Abu Dhabi with a 679 m² swimming pool hall designed to accommodate 200 pool users. The hybrid system includes a high-temperature linear Fresnel reflector (LFR) solar field, stratified thermal energy storage (TES), a single-effect LiBr–H₂O absorption chiller for cooling, a water-to-water heat pump as a backup system for the stability of cooling and heating rates, and a photovoltaic (PV) system to offset the ancillary equipment power input of the hybrid system. The system performance was simulated and validated by using hourly data from Abu Dhabi. Optimization of design/operation parameters was carried out by a multi-objective genetic algorithm to achieve the maximum coefficient of performance (COP) and the minimum levelized cost of cooling (LCOE). The initial COP and LCOE were 0.701 and 0.037 $/kWh, respectively. They were optimized to 0.825 and 0.0254 $/kWh, respectively. The annual energy balance revealed a synergistic operation of the solar field, TES, and heat pump. The lifecycle assessment was utilized to compare the proposed hybrid system with the conventional vapor-compression systems in terms of energy, cost, and CO₂ emissions, in which the proposed system proved superior over conventional systems with a positive net present value (NPV) and net zero carbon emissions. Full article

Blade tip leakage flow in gas turbines is associated with aerodynamic loss and local heat transfer variation in the tip region. In this study, the flow structure, total pressure loss coefficient, heat transfer coefficient (HTC), and film cooling effectiveness (FCE) were numerically investigated for a plane tip (PLN) and five squealer tip geometries: a conventional squealer tip (SQR), cutback squealer tip (CBS), multi-cavity squealer tip (MCS), triangular-grooved suction-side squealer tip (GSS), and multi-cavity triangular-grooved suction-side squealer tip (MGS). All configurations were compared under the same cascade geometry, tip-clearance condition, and inlet/outlet boundary conditions to examine the geometry-dependent relationship among aerodynamic loss, heat transfer, and film cooling performance. Film cooling was evaluated at blowing ratios of M = 1 and 2 using a camber-line hole arrangement, and the effect of hole rearrangement was further examined at the same blowing ratio and with the same number of cooling holes. The results indicate that the aerodynamic and thermal characteristics of the tip region vary with the leakage-flow path, cavity recirculation, and reattachment behavior formed by each tip geometry. Under the present conditions, SQR showed the lowest downstream total pressure loss coefficient, with a 7.27% reduction relative to PLN, whereas MGS showed the lowest geometry-normalized heat transfer rate among the tested geometries. Increasing the blowing ratio tended to increase FCE, although local cooling performance was affected by high-pressure or reattachment-dominated regions where coolant ejection, surface attachment, or lateral spreading was limited. Compared with the camber-line arrangement, the rearranged hole configuration increased local FCE by up to 29.6% for CBS and 23.3% for MGS at the same blowing ratio. These results may be used as comparative data for evaluating squealer tip geometries and cooling-hole placement during preliminary blade tip cooling design. Full article

Energy consumption and different methods for determining energy efficiency were evaluated for drying of extruded rainbow trout feed pellets using a pilot-scale, heated air, integrated conveyor dryer and cooler. Impact of drying parameters on product quality, especially final moisture and pellet durability index (PDI), was also studied. From an initial moisture of 21.2 to 22.1% wet basis (wb), the drying–cooling process reduced the pellet moisture to 3.5 to 5.0% wb. Dryer throughput (82–121 kg/h) did not have statistically significant impact on final moisture (p = 0.0965) although the highest throughput corresponded to highest moisture; but increase in drying temperature from 93 to 115 °C led to a significant decrease in final moisture (p = 0.0285). Increase in dryer throughput led to a significant increase in PDI from 82.8 to 88.0% (p = 0.0003), while increase in drying temperature resulted in a slight decrease in PDI from 84.3 to 83.6%, although not statistically significant (p = 0.0811). Sorghum-based aquatic feed had a slightly lower PDI than wheat-based feed (82.8 versus 83.7%, respectively), but the difference was not statistically significant (p = 0.3009). Differences in pellet durability were attributed primarily to structural weakness induced by product shrinkage during drying, which in turn was impacted by drying rates. Specific energy consumption (SEC) during drying decreased from 136.3 to 101.1 MJ/kg-water with increase in throughput and increased from 122.5 to 150.1 MJ/kg-water with increase in drying temperature. An inverse trend was observed for various measures of dryer energy efficiency, with increase in efficiency for higher throughput and decrease for higher temperature. Sorghum-based aquatic feed had a higher drying SEC as compared to wheat-based feed and a lower energy efficiency. Overall, the results highlighted trade-offs between throughput, drying efficiency and pellet quality during drying of aquatic feeds. Full article

Unsupported and weakly supported overhang features remain a critical challenge in laser powder bed fusion (LPBF) due to their strong susceptibility to geometric degradation, residual stress accumulation, and part distortion. In this study, bridge-shaped structures with four different arch sizes are fabricated to systematically investigate geometry-dependent macroscopic forming quality, stress evolution, and distortion behavior. Experimental results show that increasing arch size leads to progressive thickness reduction at the arch bottom and eventual overhang closure loss, indicating a monotonic deterioration in geometric fidelity. A thermo-mechanically coupled finite element model is developed and calibrated using 3D scanning measurements of warpage, achieving a maximum deviation below 0.03 mm between predicted and measured displacements. Numerical analyses reveal that larger arch sizes promote local heat accumulation and reduced cooling rates beneath the arch, which reduce the instantaneous load-bearing capacity of the material and increase its susceptibility to downward deformation. Meanwhile, arch size significantly influences the establishment of structural continuity and stress transfer during printing; incomplete closure in large arches interrupts load-bearing paths and alters stress redistribution at intermediate stages, whereas similar stress evolution trends are observed once geometric continuity is achieved. These findings demonstrate that arch closure acts as a key structural transition controlling stress transmission and distortion development during LPBF, thereby providing mechanistic insight into geometry-induced defects and offering quantitative guidance for the design of unsupported features in additively manufactured components. Full article

The rapid global transition toward electric vehicles (EVs) demands lithium-ion battery (LIB) systems that ensure both extreme performance and uncompromising safety. However, the inherent thermal asymmetry within battery packs—driven by non-uniform heat generation and localized hotspots—remains a critical bottleneck, accelerating degradation and triggering thermal runaway. Phase change materials (PCMs) have emerged as pivotal thermal buffers due to their high latent heat capacity and ability to maintain passive thermal symmetry. This review provides a comprehensive analysis of recent advancements in PCM-based battery thermal management systems (BTMSs), transitioning from material-level nanostructural enhancements to system-level hybrid architectures. Unlike traditional reviews, we critically evaluate how the integration of multidimensional conductive fillers and advanced encapsulation technologies resolves the trade-offs between energy density and thermal response rates. Furthermore, the synergistic coordination between PCMs and active cooling strategies (liquid, air, and heat pipes) is synthesized to provide a roadmap for achieving global thermal equilibrium under extreme fast-charging (XFC) conditions. Full article

To enhance the energy efficiency of data center cooling systems, this study introduces Micro-encapsulated Phase Change Material Suspension (MPCMS) into a naturally stratified cold storage system. Leveraging its superior properties, including high latent heat, high specific heat, and excellent fluidity, a three-dimensional transient numerical model was developed to investigate the thermal stratification characteristics during the discharging process. The analysis focuses on the impacts of operational conditions (flow rate and mass fraction) alongside key tank structural parameters (height-to-diameter ratio, uniform flow plate perforation rate, installation position, and aperture). The results indicate that the thermal stratification performance of MPCMS is significantly superior to that of water. Specifically, during the middle discharge stage (t* = 0.4) at a high flow rate of 12.56 m³/h, the thermocline thickness of MPCMS-10 wt% is restricted to only 245 mm, representing a 93.82% reduction compared to 3964 mm for water. Furthermore, at the initial discharge stage (t* = 0.05), the thermocline thickness decreases significantly with increasing MPCMS mass fraction; as the mass fraction rises from 10 wt% to 30 wt%, the thickness sharply drops from 421 mm to 120 mm (a 71.44% reduction), and the stratification number (Str) reaches an optimal 1.00. In terms of macroscopic structural optimization, a height-to-diameter (H/D) ratio between 2 and 4 provides the best balance of stratification stability and cold storage efficiency. Mechanistically, integrating a uniform flow plate effectively suppresses thermal jet disturbances. During the initial discharge stage, a plate with a 10% perforation ratio reduces the thermocline thickness by 69.12% (from 421 mm to 130 mm) relative to the no-plate baseline. The optimal flow plate configuration was identified as a 10% perforation rate, a 20 mm aperture, and an installation spacing of 1.25% of the tank height. Ultimately, this study validates the substantial potential of MPCMS through robust quantitative data, providing a solid theoretical foundation and precise design guidelines for high-efficiency cold storage systems. Full article

Background/Objectives: Since June 2025, Japan has mandated countermeasures to prevent outdoor laborers from developing heat-related illness at work. However, the extent to which preventive behaviors can reduce the actual heatstroke risk has not been quantified. The present study aimed to (i) project future trends in the daily number of heat-related ambulance transports in the working population under climate change, and (ii) evaluate the population-level preventive impact of workplace-adopted preventive behaviors using effect estimates from observational data. Methods: Using daily maximum wet-bulb globe temperature, a long-term future projection of heat-related ambulance transports was performed in the working population. A cross-sectional survey was carried out to infer the effect size of behavioral interventions. The effectiveness of taking preventive behaviors was evaluated by increasing the coverage rate of workers adhering to all four behaviors (current: 23%): (i) regular hydration, (ii) use of an air-cooling vest, (iii) checking their own health condition before work, and (iv) recognizing warning signs. Theoretical scenarios in which workplace instructions to workers or teams increased adherence by 50%, 100%, and 300% relative to baseline were considered, corresponding to coverage rates at 34%, 45%, and 91%, respectively, and we evaluated the associated reduction in heatstroke risk. Results: Many future years were projected to have higher annual levels of heat-related ambulance transports than the median value from 2018–2024, indicating a long-term increasing trend. Even when all four possible countermeasures were implemented at an additional 50%, 100% or 300% from the current rate, the expected relative risk reduction in transports was 3.2%, 6.3%, and 19.0%, respectively, indicating only a small effect on future projected heat-related illnesses. Conclusions: The number of heat-related ambulance transports is expected to increase; however, the relative risk reduction with behavioral intervention is likely limited. A fundamental overhaul of working regulations and environment (e.g., drastic shift in working hours to earlier morning) is required via adaptation policies, and mitigation of climate change is vital. Full article