Miniaturised, high-power satellite avionics require effective waste-heat management, especially in low-Earth orbit (LEO), where sunlight–eclipse transitions impose high-amplitude thermal cycles. Phase change material (PCM) heat sinks can mitigate these fluctuations through latent heat storage, while additive manufacturing enables integration with triply periodic minimal surface (TPMS) architectures to enhance heat transfer. However, experimental in-orbit operation of TPMS-PCM heat sinks has not yet been demonstrated. This work presents the first11Scopus search string: “TITLE-ABS-KEY(PCM AND TPMS AND orbit)”; Web of Science all fields search “PCM TPMS orbit” returned zero results on 10th Jan 2026. in-orbit demonstration of a TPMS heat sink with 7.0 g of paraffin wax PCM. Flown aboard the Matilda payload on Waratah Seed-1 (WS-1), the TPMS-PCM module was benchmarked against a conventional radial-finned heat sink without PCM. Terrestrial high-grade thermal vacuum tests closely matched in-orbit heating profiles, suggesting no dominant module-level deviation in PCM melting behaviour for the investigated conditions, geometry, and scale. The TPMS-PCM module extended the operational time to reach 85 °C by 85% on Earth and 92% in orbit, with a mass increase of 16% (PCM mass relative to metallic mass). During idle operation, peak-to-valley temperature fluctuations were reduced by up to 2.9 °C, demonstrating effective thermal buffering of orbital temperature cycles. The influence of orbital position and solar exposure was quantified at multiple power levels, revealing stronger sensitivity to illumination conditions at lower power inputs. Overall, the results demonstrate the potential of TPMS-PCM heat sinks for mass-efficient CubeSat thermal management and support the use of terrestrial thermal-vacuum testing as a useful ground-based reference for module-level performance assessment.

The K-Nearest Neighbors algorithm is a widely used machine learning technique for classification and regression tasks due to its simplicity, interpretability, and effectiveness. However, KNN suffers from the curse of dimensionality and increased computational complexity when applied to high-dimensional datasets. This paper proposes an adaptive algorithm, termed PCA-RF-WKNN. It combines Principal Component Analysis and Random Forest-based feature weighting to address the challenges of KNN in high-dimensional spaces. The method reduces computational complexity by lowering the number of dimensions and improves distance calculations through weighted features. The algorithm dynamically selects the optimal number of neighbors (k) and PCA components (m) based on cross-validation. A comprehensive evaluation across four high-dimensional classification benchmark datasets—including SECOM semiconductor manufacturing, LSVT Voice Rehabilitation, Steel Plates Faults, and Leukemia Gene Expression—shows that PCA-RF-WKNN consistently outperforms both PCA-KNN and standard KNN. The statistical significance of the observed performance improvements is validated using the paired Wilcoxon signed-rank test. The primary experimental evaluation was conducted on the SECOM dataset. The results demonstrate that the proposed PCA-RF-WKNN model achieves the highest testing accuracy of 0.962, outperforming both PCA-KNN (0.923) and standard KNN (0.863). The ROC curve for PCA-RF-WKNN rises steeply toward the top-left corner, indicating strong classification capability, with an AUC of 0.900, compared to 0.816 for PCA-KNN and 0.701 for KNN. The PCA-RF-WKNN model outperforms the benchmark models across all key performance metrics, including accuracy, precision, sensitivity, F1-score, and ROC-AUC. Overall, the proposed approach significantly enhances KNN performance, surpasses PCA-KNN, and provides a promising solution for high-dimensional data problems.

Barocaloric materials promise eco-friendly alternatives to vapour compression in refrigeration, with (C9H19NH3)2CuBr4 being a focus of this study. It is a highly promising barocaloric refrigerant due to the 0.4 K hysteresis temperature and operational pressure as low as 500 Bar. A reversible and irreversible Brayton Barocaloric refrigeration cycle analysis is established. For the irreversible cycle, the irreversibility during the compression and expansion process is considered in the two adiabatic processes. Performance characteristics are investigated across various indoor and outdoor temperature ranges, material operational temperature points, and operating pressures to determine the Coefficient of Performance (COP) and Dimensionless Refrigeration Capacity (DRC). The guidance for optimising the irreversible Brayton Barocaloric refrigeration cycle analysis is provided by disclosing the impact of the irreversibility of work process efficiency, timing ratio, and heat reservoir temperatures. Moreover, several specific cases are examined in detail. The results demonstrate that maximising the phase transition region of (C9H19NH3)2CuBr4 results in a COP of 10.8 achieved at a temperature span of 3.5 K while maintaining a 0.9-time ratio and conservative irreversibility efficiency of 0.8. This material is capable of cooling by 5.0 K with a reasonable COP of 2.5 at the 0.75-time ratio for a heat source temperature of 309 K and heat sink temperature of 314 K. Finally, this study demonstrates the potential for constructing a simple Barocaloric refrigeration system to validate the concept, with opportunities for further improvement through modifications.

With the rapid expansion of small satellite constellations in Low Earth Orbit (LEO), the demand for resilient computing and high-power electronics in telecom, surveillance, and scientific applications is rising. With increasing power densities, these systems face critical thermal challenges due to the absence of convective cooling and limited surface area for heat dissipation. Effective thermal management solutions are crucial for preventing overheating and ensuring mission longevity. This study presents a rare in-orbit performance assessment of an additively-manufactured triply periodic minimal surface (TPMS) heat sink with phase change material (PCM) for CubeSat thermal control. The University of Technology Sydney and Mawson Rovers' payload Matilda, launched aboard Waratah Seed-1 satellite in August 2024, integrates a thermal management module comprised of a 3D-printed aluminium TPMS structure with paraffin wax PCM, leveraging both the TPMS's high surface-area-to-volume ratio for enhanced heat transfer and the PCM's latent heat storage capacity. To establish a performance baseline, the payload also includes a conventional heat sink with radial planar fins without PCM, representative of widely-used terrestrial cooling solutions, and fabricated with identical metallic mass to the IWP TPMS heat sink. A comprehensive experimental analysis compares the in-orbit thermal behaviour of both modules, while a reduced-order numerical model enables rapid predictions of thermal performance with low computational effort. Results demonstrate that the TPMS-PCM-based module increased the time required for the electronics to reach an 85 degrees C setpoint temperature by 77% relative to the finned reference module. This substantial operating time extension was reached with an additional 7.0 g of PCM, which corresponds to only 16% mass increase relative to the mass of the metallic heat sinks, highlighting the effective performance of the TPMS-PCM-based thermal management module as a lightweight, high-impact solution. In addition, the reduced-order numerical model reproduced the overall transient orbital response with good agreement. These findings validate TPMS-PCM heat sinks as a scalable, lightweight thermal management solution for CubeSats, offering a pathway to extended operating time and enhanced reliability in next-generation small satellite missions.

Maintaining satellite electronics within their maximum allowable operating temperatures is crucial for longterm reliability, yet increasingly power-dense payloads and miniaturized satellites introduce severe challenges. To meet the demand for efficient thermal management, this study leverages advances in additive manufacturing and explores triply periodic minimal surface (TPMS) heat sinks with phase change material (PCM) for space use, a growing area but with limited research. As part of the design development of the University of Technology Sydney's payload Matilda, this work examined how geometry, material composition, and orientation influence the performance of PCM-based thermal management modules. Five heat sink designs were investigated: hollow, gyroid, I-graph-Wrapped Package-graph (IWP), swirl, and radial plane fins. The heat sinks were 3D-printed from titanium and stainless steel, filled with paraffin wax PCM, and tested under vacuum at two power levels. Key parameters such as internal surface area and mass were analysed. Results show that, although material thermal conductivity influences temperature, design-dependent factors such as total metallic mass and internal structure distribution dominate heat dissipation. The gyroid achieved the lowest temperatures, though at the cost of increased mass, while mass-normalized performance identified the IWP lattice and radial-finned designs as most efficient. A mass-matched comparison of these two revealed nearly identical performance despite 27% difference in internal surface area, underscoring the role of total mass and internal geometry distribution. Orientation and initial PCM position had minimal influence, with less than 4 degrees C variation. These findings demonstrate that thermal performance is heavily affected by material properties, total mass, and structure distribution, with geometric complexity offering secondary benefits, and orientation and PCM position yielding minimal returns.

Efficient monitoring and prediction of appliance energy consumption in low-energy houses are important for optimizing building performance and advancing smart energy management. Wireless sensor networks (WSNs) provide high-resolution indoor environmental data; however, the resulting datasets are often high-dimensional, redundant, and nonlinear, posing challenges for conventional regression models. This paper proposes a hybrid regression framework, termed Lasso-RF-Net, which combines linear feature selection and nonlinear adaptability in a computationally efficient manner. The first stage identifies a sparse linear structure and reduces dimensionality, while the second stage captures nonlinear interactions through residual learning. The proposed model was evaluated using a real-world low-energy house dataset incorporating indoor WSN measurements and outdoor weather variables, and further validated on three benchmark regression datasets. Results show that Lasso-RF-Net achieves the lowest testing mean squared error compared with Lasso, Random Forest, Subset Selection, and Deep Neural Networks, while maintaining a moderate computational cost. Feature analysis indicates that kitchen humidity and laundry-room temperature are dominant indoor predictors, whereas outdoor humidity and wind speed are the most influential weather variables. Overall, the proposed framework provides an accurate, computationally efficient, and interpretable solution for high-dimensional nonlinear energy prediction problems.

Thermal control of lithium-ion batteries remains a key challenge for electric vehicles, especially during fast charging and sustained heat generation. This study presents a numerical investigation of fin-assisted phase change material (PCM) based passive cooling systems using Rubitherm RT-42, RT-50, and their 5% Al₂O₃ nano-enhanced versions. Two triplex tube designs are analyzed: Model 1 with a single PCM layer and combined cylindrical and radial fins, and Model 2 with a double-layer PCM arrangement and dual cylindrical fins. The melting process is simulated using the enthalpy–porosity method under a constant heat flux of 1000 W/m2, considering transient conduction and natural convection. Results show that the integrated geometric configuration has the strongest influence on melting behavior and thermal performance. Model 2 reduces complete melting time by 14 to 19.5% compared to Model-1 and lowers the melting completion temperature by about 4 K. It also improves temperature uniformity and reduces thermal stratification inside the PCM domain. PCM type mainly influences activation timing and buffering duration. RT-42 melts earlier and maintains temperatures 4 to 6 K lower during phase change, but shortens buffering time by up to 10.2 min relative to RT-50. RT-50 provides 9 to 14% longer latent heat protection under continuous heating conditions. Nano-enhancement has limited impact on melting time but reduces peak temperature at 60 min by up to 7.3 K in Model 1 and 5.8 K in Model 2 by enhancing internal heat diffusion. Overall, geometry, melting temperature, and nano loading must be selected together to balance rapid temperature control and extended passive cooling performance.

The thermal management of electronics in space presents unique challenges due to high waste heat generation, miniaturised device footprints, and the absence of convective cooling in vacuum environments. This study investigates the behaviour of a metallic heat sink under varying pressure conditions, from atmospheric pressure to high-grade vacuum, using experimental and numerical approaches. The thermal response of a stainless steel heat sink featuring plate fins was investigated at two power levels to simulate different heat loads of satellite avionics. The experiments revealed a significant rise in operating temperatures under lower pressure conditions, with temperatures in high-grade vacuum exceeding those at atmospheric pressure by up to 66%. A reduced-order numerical model was formulated and validated against experimental data, demonstrating strong agreement and providing an efficient tool for predicting heat sink performance in vacuum conditions. The findings underscore the critical impact of pressure on heat dissipation mechanisms and highlight the need for advanced thermal management strategies tailored for space applications. This work contributes to the understanding of heat sink behaviour across varying pressure environments, offering insights for the design of more effective thermal control in aero-and astrospace technologies.

The advantages of a high storage capacity and safety of metal hydride hydrogen storage (MHHS) have widely attracted people's interest in hydrogen storage. The improvement of the heat transfer performance is one of the key parameters to improve the overall MHHS performance. Various heat exchangers with complex structures have been developed for this purpose. However, the drawback of these heat exchangers is huge pressure losses. Therefore, this study aims to enhance the MHHS performance by considering the heat transfer improvement and maintaining the pressure loss inside the heat exchanger. To fulfil the requirement of heat transfer efficiency instead of using complex heat exchangers, a novel triple-branched fin is designed to attach to the simple straight tube heat exchanger. The effect of pressure losses due to the complex heat exchangers is analysed and compared with the simple straight tube. The novel fin heat exchanger's performance is also compared to conventional fins. Moreover, an enhancement of the novel fin geometries is considered with the parametric studies to achieve superior MHHS performance. The results indicate that the pressure losses are reduced by 31 % when using the straight tube instead of other complex heat exchangers. The novel triple-branched fin obtains the best heat transfer performance compared to other fin designs, including the quadrilateral fin and Y-shaped fin. After the geometrical enhancement of this novel fin, the duration of the absorption-desorption cycle is reduced by 25 % compared to the quadrilateral fin. Under the parametric study, heat transfer fluid temperature significantly affects the desorption process, while the heat transfer coefficient greatly affects the absorption process.

The rapid miniaturization of modern electronics has led to significant overheating issues, which pose substantial risks to their performance, reliability, and service life. This study aims to address these challenges by proposing a novel heat sink design incorporating Triply Periodic Minimal Surface (TPMS)-based metal lattice structures embedded with a phase change material (PCM). A comprehensive numerical and experimental investigation was conducted on a 3D-printed PCM metal-lattice heat sink. By employing a three-dimensional unsteady numerical approach and the finite volume method, this study evaluated the metal lattice as a thermal conductivity enhancer. A parametric study was performed to assess the impacts of the heater power input, material, design, and applied heat flux direction. The tested materials were Stainless Steel (SS) and titanium (Ti), with paraffin wax as the PCM. The findings demonstrated that the TPMS-based lattice structure (P3) helps improve the heat exchange between the metal and PCM by facilitating gradual and uniform melting within the system. The SS (P3) heat sink showed up to a 9 % reduction in base temperature compared to Ti (P3) under heater power inputs ranging from 5.1 W to 8.6 W, attributed to its better thermal conductivity. The parametric analysis indicated that, when compared to radial fin design (P5) under multidirectional heat input, P5 returns 3 to 4 degrees C lower base temperature than P3 for SS and Ti under base-only heating case scenario. On the contrary, P3 outperformed P5 by maintaining side walls 6 to 8 degrees C cooler during side-only heating. However, the combined effect of base and side heating was found to be insignificant for both designs. The analysis concluded that although the radial fin design (P5) performs slightly better under base-only heating conditions, the TPMS design (P3) would otherwise outperform it, particularly in applications involving multi-directional heat input.

Heat exchangers are critical components in various industrial applications, requiring efficient thermal management to enhance thermal performance and energy efficiency. Longitudinal vortex generators (LVGs) have emerged as a potent mechanism to enhance heat transfer within these devices. A precise knowledge of the thermal performance enhancement of HE through LVGs is missing in the literature. Therefore, this study aims to provide a critical review of both numerical simulations and experimental studies focusing on the enhancement of heat transfer through LVGs to further enhance the knowledge of the field. It begins with elucidating the fundamental principles behind LVGs and delineating their role in manipulating flow patterns to augment heat transfer. This is followed by an exploration of the various numerical methods employed in the field, including computational fluid dynamics techniques such as Reynolds-Averaged Navier–Stokes (RANS) models, Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS). Various experimental methods are then summarised, including differential pressure measuring instruments, temperature measurements, velocity measurements, heat transfer coefficient measurements, and flow visualisation techniques. The effectiveness of these methods in capturing the complex fluid dynamics and thermal characteristics induced by LVGs is critically assessed. The review covers a wide range of LVG configurations, including their geometry, placements, and orientations, and their effects on the thermal performance of heat exchangers. Different from previous reviews that mainly focus on classical configurations and historical studies, this review also emphasizes recent developments in computational fluid dynamics and progress in interdisciplinary fields such as innovative materials, additive manufacturing, surface finishing, and machine learning. By bridging the gap between fluid dynamics, thermal enhancement, and emerging manufacturing technologies, this paper provides a forward-looking, comprehensive analysis that is valuable for both academic and industrial innovations.

This study investigates the thermal performance of Triply Periodic Minimal Surface (TPMS)-based metal lattice heat sinks integrated with three Phase Change Materials (PCMs): RT55, RT42, and RT31. The objective is to optimize thermal management for high-performance electronics by evaluating the influence of PCM thermal properties and lattice geometry on heat transfer and phase change dynamics. Four TPMS-based designs octahedral (P3), waveform (P2), droplet (P4) and primitive (P6) were numerically analyzed under unidirectional heat flux conditions using a finite volume method. The simulations considered transient base and average temperature profiles, liquid fraction progression, and time to complete melting. Results revealed that primitive design consistently outperformed other configurations, achieving the lowest base temperature of 72 degrees C with RT31 and completing phase change in just 491 s, 28 % faster than waveform design and over 50 % faster than droplet design. Conversely, droplet design exhibited the slowest thermal response, with a base temperature of 90 degrees C and a melting time exceeding 3500 s for RT55. Among the PCMs, RT31 demonstrated superior thermal buffering due to its lower melting temperature, stabilizing average temperatures at least 5 degrees C lower than RT42 and RT55. The study highlights the importance of symmetrical lattice structures, such as in primitive design, for enhancing heat transfer efficiency and reducing phase change duration. This work contributes to advancing TPMS-based heat sink designs and provides actionable insights for integrating PCMs into next-generation thermal management systems for energy storage and electronics cooling.

High computational power and miniaturisation of modern electronics lead to high heat generation, compounded by the decreased available area for heat dissipation. This challenge is exacerbated in space environments due to the lack of convection. Phase change materials (PCM) are a strong option for the passive thermal management of satellites. However, their behaviour in vacuum is unclear. This study experimentally investigates and compares the performance of non-PCM and PCM-based thermal control modules under atmospheric pressure and vacuum conditions. A stainless steel heat sink with internal planar fins was tested using a printed circuit board (PCB) to produce three input power levels, simulating the heat dissipated by satellite electronics. Paraffin wax was used as the PCM. The thermal performance is reported and analysed for both pressure conditions. A reduced-order numerical model was established to predict performance with low required computational effort. This work finds that electronics operating in vacuum displayed temperatures as much as 32.8% higher compared to those in atmosphere due to decreased heat dissipation resulting from the lack of convective heat transfer. In addition, PCM had a greater impact in reducing the electronics temperature in vacuum than at atmospheric pressure. The presence of 6 g of PCM lowered the electronics temperatures by up to 18.0 degrees C in vacuum, and by up to 12.3 degrees C in atmospheric pressure. That amount of PCM doubled the electronics operating time under both pressure conditions at high power. The findings of this work contribute to understanding the performance variances of non-PCM and PCM-based heat sinks under different pressure conditions to further improve the design of thermal management modules for satellites.

The early development of refrigeration technology relied on natural refrigerants such as carbon dioxide (CO2), ammonia, and hydrocarbons. However, technical limitations and safety challenges led to their replacement by synthetic refrigerants. With increasing environmental concerns over high global warming potential (GWP) synthetic refrigerants, renewed attention has turned to natural alternatives, particularly CO2, valued for its non-flammability, low toxicity, and negligible GWP. Despite these advantages, CO2's low critical temperature (30.98 degrees C) restricts its efficiency in air conditioning applications, as it often requires operation in transcritical cycles that are inherently less efficient. This study introduces a novel integration of a CO2 air conditioning heat pump (CO2-ACHP) with an Earth-Air Heat Exchanger (EAHE) to overcome this limitation by maintaining the condensing temperature below CO2's critical point, thus enabling more efficient subcritical operation. A mathematical model was developed to simulate the subsoil thermal behaviour in Sydney, Australia, revealing stable ground temperatures between 15.5 degrees C and 20.1 degrees C at a depth of 2.5 m. Using a 35-m-long PVC pipe, the EAHE provided an outlet air temperature of approx-imately 19.5 degrees C, effectively reducing the CO2 condenser temperature and improving system performance. The proposed CO2-ACHP/EAHE system demonstrated a 30 % improvement in coefficient of performance (COP) compared to conventional R-410A systems and achieved a 59 % enhancement relative to a CO2 transcritical system. Correspondingly, total equivalent warming impact (TEWI) decreased by 32 % compared to R-410A and 59 % compared to the transcritical CO2 baseline. These results confirm the system's potential as an energy-efficient and environmentally sustain-able alternative for air conditioning, introducing a novel pathway for enhancing CO2 cycle effi-ciency through passive ground temperature regulation.

Metal hydride-based hydrogen storage (MHHS) has been used for several purposes, including mobile and stationary applications. In general, the overall MHHS performance for both applications depends on three main factors, which are the appropriate selection of metal hydride material uses, design configurations of the MHHS based on the heat exchanger, and overall operating conditions. However, there are different specific requirements for the two applications. The weight of the overall MHHS is the key requirement for mobile applications, while hydrogen storage capacity is the key requirement for stationary applications. Based on these requirements, several techniques have been recently used to enhance MHHS performance by mostly considering the faster hydrogen absorption/desorption reaction. Considering metal hydride (MH) materials, their low thermal conductivity significantly impacts the hydrogen absorption/desorption reaction. For this purpose, a comprehensive understanding of these three main factors and the hydrogen absorption/desorption reaction is critical and it should be up to date to obtain the suitable MHHS performance for all related applications. Therefore, this article reviews the key techniques, which have recently been applied for the enhancement of MHHS performance. In the review, it is demonstrated that the design and layout of the heat exchanger greatly affect the performance of the internal heat exchanger. The initial temperature of the heat transfer fluid and hydrogen supply pressure are the main parameters to increase the hydrogen sorption rate and specific heating power. The higher supply pressure results in the improvement in specific heating power. For the metal hydride material selection under the consideration of mobile applications and stationary applications, it is important to strike trade-offs between hydrogen storage capacity, weight, material cost, and effective thermal conductivity.

The rising global warming potential (GWP) of refrigerants, particularly R-410A and R-134a, has driven the urgent need for environmentally friendly alternatives in cooling and heating systems. While low-GWP refrigerants are increasingly available for large and small refrigerant charge systems, a significant gap remains in identifying viable replacements for medium-charge applications, particularly in high and moderate climate conditions. This study addresses this critical gap by evaluating 15 lower GWP refrigerant options, including hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), hydrochlorofluoroolefins (HCFOs), and hydrocarbons (HCs). The analysis focuses on their direct and indirect environmental impacts, ease of design integration, operational parameters such as capacity and efficiency, and economic feasibility. A novel aspect of this work is including internal heat exchanger performance as a function of refrigerant properties, offering unique insights into how system design can influence cycle efficiency. Key findings reveal that while several refrigerants can effectively replace R-410A in chiller applications, variable refrigerant flow systems present greater challenges due to performance and safety considerations. R-447A exhibits superior performance in standard ambient conditions among the studied refrigerants, whereas R-454B is better suited for high ambient environments. Additionally, refrigerants such as R-1233zde, R-1234yf, R-1234zee, R-1234zez, R-1243zf, and R-1336mzz(Z) demonstrate significantly lower total environmental weighted impact compared to R-410A, emphasizing their potential for reducing environmental harm. This study advances the current understanding of medium-charge refrigerant applications, providing actionable insights for researchers, policymakers, and manufacturers navigating the transition away from high-GWP HFCs.

Isentropic efficiency is a common performance measure for compressors and is useful for modelling the behaviour of real compressors in relation to discharge temperature or required mechanical power input. However, it has a weakness in that a basic assumption in the calculation is that the real compressor is adiabatic. If significant heat transfer from the compressor to the outside environment occurs, then the adiabatic assumption is invalid, but the negative effects of internal entropy generation are reduced, and in principle it is possible to have a measured isentropic ‘efficiency’ greater than 100%, which, while counterintuitive, is highly desirable. We practically demonstrate this effect with an air-cooled swashplate compressor and propose that for cases of intentional compressor cooling, the simple definition for isentropic efficiency is retained as a performance measure but renamed to isentropic performance coefficient (IPC).

While forced-air convective systems remain the predominant method for heating and cooling worldwide, radiant cooling and heating systems are emerging as a more efficient alternative. Current radiant cooling systems primarily rely on hydronic chilled water systems. This study introduces direct-expansion radiant cooling as a novel technique that could enhance the efficiency of radiant cooling and reduce its environmental impact. Water (R-718) has been tested as a refrigerant due to its favorable thermodynamic properties and environmental advantages; however, to the author’s knowledge, it has yet to be tested in direct-expansion radiant cooling. This research investigated several refrigerants, including water (R-718), ammonia (R-717), R-410a, R-32, R-134a, and R-1234yf, for this application. The findings indicate that water demonstrates efficiency comparable to other non-natural refrigerants, making it a promising candidate, given its favorable thermodynamic properties and substantial environmental benefits. Despite challenges such as a high compression ratio necessitating multi-stage compression, a high compressor discharge temperature exceeding 300 °C and requiring specialized blade materials, and a high suction volume flow rate, direct-expansion radiant cooling operates within a different temperature range. Consequently, the compressor discharge temperature can be reduced to 176 °C, and the compression ratio can be lowered to approximately 3.5, making water a more viable refrigerant option for this application.

Metal hydride storage system (MHSS) has been widely used mostly because of its large storage capacity and high degree of safety. The improvement of the heat transfer performance is one of possible techniques to enhance the overall MHSS performance. The well arrangement of the heat exchanger structure from a semi-cylindrical coil heat exchanger with central return tube (SCHE-CR) significantly reduces the hydrogen absorption duration. However, the modelling of the thermal behaviour for the SCHE-CR during desorption process is missing in the literature. Therefore, this study aims to develop a model for both hydrogen absorption and desorption processes and analyse the thermal performance during the cycle. Phase change material (PCM) is incorporated with the heat exchanger for further improvement of the MHSS performance. The storage is designed under three different PCM configurations, including PCM jacket, pool bed, and capsule. The numerical results report that the duration of the absorption-desorption cycle is reduced by over 50% when using SCHE-CR instead of a helical coil. The PCM configurations, especially the PCM capsule, increase the MHSS performance, especially during the absorption. The duration of one cycle is decreased by at least 39% when combining the SCHE-CR with PCM. The HTF temperature significantly affects the MHSS performance, especially during the desorption. Reduction in HTF temperature reduces the absorption duration by at least 15%, while increasing the HTF temperature reduces the desorption duration by at least 25%. The new MHSS configuration would be beneficial to enhance the heat exchange during the absorption-desorption cycle of industrial MHSS applications.

The recent advancements in miniaturization and multi-functionality of electronics have increased overheating risks, leading to unreliable performance and higher operating temperatures. To address this, a comprehensive numerical and experimental analysis of a 3D printed, stainless-steel, phase change material (PCM) radial fin heat sink design was performed. A three-dimensional unsteady numerical approach based on the finite volume method investigated the use of radial fins as thermal conductivity enhancers. A parametric study evaluated factors including power input, convective heat transfer coefficient, base thickness, fin thickness, and fin height. Paraffin wax was used as the PCM. To replicate the heat output of electronic devices, a constant power input was supplied to the heat sink base, capturing transient profiles of base temperature, volume average temperature, liquid-fraction, and velocity distributions. Results indicate that power input, convective heat transfer coefficient, and base thickness significantly influence performance more than fin thickness and height. Base temperature reductions with increased heat transfer, lower power input, and thicker bases were 81 %, 34.9 %, and 14.1 % respectively, while thicker and taller fins resulted in 4.3 % and 0.5 % reductions after 2000 s. The study suggests improved cooling performance with higher convective heat transfer coefficient (20 W/m2K < HTC < 40 W/m2K), thicker bases (2 mm < tbase < 3 mm), and thicker fins (1.5 mm < tfin < 2.5 mm) at constant power input. These findings contribute to the design and development of efficient heat sinks for high-power modern electronics.