最新刊期
- 摘要：ObjectiveThermal management is crucial for ensuring the performance， safety， and longevity of proton exchange membrane fuel cells （PEMFCs）. While excessively high temperatures can degrade the membrane electrode assembly and cause irreversible damage， excessively low temperatures impede reaction kinetics and may even lead to flooding. Consequently， it is essential to implement appropriate thermal management strategies to maintain the operating temperature of PEMFCs within an optimal range and ensure a uniform temperature distribution inside the stack. However， air cooling tends to produce uneven temperature distributions along the flow path due to the low specific heat capacity of air. Liquid cooling requires pumps to drive the coolant through the cooling channels， which incurs additional parasitic power losses and thereby reduces overall system efficiency. To mitigate the parasitic power consumption associated with conventional air and liquid cooling， this study proposes a novel passive cooling scheme that integrates vapor chambers （VCs） into a PEMFC stack for thermal management.MethodsBoth theoretical analysis and experimental approaches were employed to evaluate the heat transfer performance of a standalone VC and a fuel cell stack integrated with VCs. First， the heat generation and transfer mechanisms within the fuel cell and heat transfer characteristics of the VC were analyzed. Based on the capillary force limit， the relationship between the structural dimensions of the VC and its maximum heat transfer capacity was determined. Subsequently， an ultra-thin VC with a heat transfer capacity exceeding 40 W and thickness of only 1.32 mm was designed and manufactured according to the heat dissipation requirements of a 200 W open-cathode PEMFC stack. In the thermal performance test of the single VC， a silicone heating pad was bonded to the VC's evaporator side using thermal grease. The heating power was varied from 0 to 48 W using a resistive load to simulate PEMFC heat generation. Additionally， a custom-made aluminum alloy cold plate was attached to the VC's condenser side to dissipate heat， with the cooling water flow rate maintained at 0.1 L/min. Twenty-four thermocouples were evenly spaced at 20-mm intervals on the opposite face of the VC. Temperatures were recorded via a data logger and subsequently transmitted to a computer for storage and analysis. After verifying the heat dissipation capability， five VCs were integrated into a 200 W PEMFC stack to conduct a rapid start-up load test， where the current was ramped from 0 to 40 A within 45 s. A thermocouple was installed in the cathodic central flow channel of the cathode of each cell to monitor temperature variations. The hydrogen supply pressure at the anode was 0.05 MPa， and the oxygen flow rate at the cathode was 0.03 m³/s. The ambient temperature and relative humidity were 26.3 ℃ and 63%， respectively.Results and DiscussionsIn the single VC test， when the heating power was varied， the VC rapidly reached a new equilibrium state within each 6-min test cycle， demonstrating excellent thermal response. From 0 to 48 W， the maximum temperature difference across the VC consistently remained below 3 ℃. At 48 W （a heat flux of 22.7 W/cm² across the VC cross-section）， the maximum temperature difference was only 2.6 ℃， and the thermal resistance was 0.054 ℃/W， exhibiting a downward trend with increasing heat load. These results indicate that the manufactured VC possesses excellent temperature-equalizing capability. Following the start-up test， the average output voltage of the VC stack was 5.27 V， compared with 4.33 V for the conventional stack， representing a 21.7% improvement. The temperatures of 10 cells in the VC stack ranged from 47.0 to 52.5 ℃， yielding a maximum inter-cell temperature difference of 5.5 ℃. In contrast， the cells in the conventional stack exhibited a range of 53.2 to 63.3 ℃， with a maximum inter-cell temperature difference of 10.1 ℃. The integrated VC effectively prevented performance degradation arising from non-uniform stack operating temperatures.ConclusionsTo improve the thermal management of PEMFC stacks， this study integrates a passive heat transfer unit， namely， a VC， into an open-cathode fuel cell stack. The fabricated VC operates at a heat flux of only 0.052 W/cm2 on the evaporator side and exhibits a thermal resistance of only 0.054 ℃/W under a heat load of 48 W， demonstrating excellent thermal response and heat transfer performance. The integration of the VC into the stack enables rapid dissipation of heat generated by electrochemical reactions while maintaining a uniform temperature distribution throughout the stack. This approach effectively mitigates performance degradation arising from inadequate thermal management， thereby providing a valuable reference for optimizing the thermal management design of automotive fuel cell stacks.关键词：automotive fuel cell stack;thermal management;vapor chamber;performance consistency2|0|0更新时间：2026-09-14
- 摘要：To elucidate the phase-transition process of the supercooled water inside an ultrasonic crystallization accelerator， a coupled computational fluid dynamics-population balance model （CFD-PBM） is established by combining a Euler-Euler multiphase flow model， a population balance model （PBM）， and a user-defined function. This model is adopted to numerically simulate the fluid flow， nucleation， and ice-crystal growth within a swirling ultrasonic crystallization accelerator. The simulation results reveal that the ice volume fraction at the outlet increases firstly and then stabilizes with the increasing ultrasonic power， accompanied by a slight decline under several high-power operational conditions. At 200-450 W， the optimal ultrasonic power increases with the flow rate. Increasing the ultrasonic frequency intensifies the thermal effect while reducing the volume fraction of ice at outlet： the lower frequencies between 20 and 40 kHz are more favorable for ice crystallization. The swirling structure prolongs the residence time of supercooled water， strengthens the ice–water mixing， and accelerates the supercooling elimination. By comprehensively considering the volume fraction of ice at outlet， heat loss， and ultrasonic transmission loss， the optimal operational parameters are determined to be an ultrasonic power of 360 W and a frequency of 25 kHz. The findings of this study can provide theoretical guidelines for the structural design of crystallization accelerators in dynamic ice thermal-storage systems.关键词：ultrasonic nucleation;CFD-PBM coupled model;supercooled water;ice crystal evolution;dynamic ice storage1|0|0更新时间：2026-09-14
- 摘要：Conventional reverse-cycle defrosting technology exhibits disadvantages such as low defrosting efficiency， poor thermal comfort， and significantly reduced compressor lifespan due to frequent compressor start-stop cycles. To address these challenges， this study develops a coordinated control strategy for the compressor， electronic expansion valve， and four-way valve based on conventional reverse-cycle defrosting， thus enabling rapid defrosting without compressor shutdown. Comparative tests were conducted using an experimental platform under variable operating conditions. The results demonstrate that the proposed strategy achieves efficient non-stop reverse-cycle defrosting with higher reliability and mitigates damage to the compressor. Through comparative testing of four parameter schemes， design principles for parameter optimization were established. Scheme 2 exhibited the best performance： under frosting-prone conditions， it improved heating capacity by 13%， reduced discomfort level by 60%， and extended operational-cycle duration by 38%. This study provides an optimized technical pathway for the stable and highly efficient operation of heat pumps in low-temperature environments， thereby enhancing thermal comfort and offering strong potential for widespread engineering adoption.关键词：reverse cycle defrosting;non-stop reversing;collaborative control;air-source heat pump1|0|0更新时间：2026-09-14
- 摘要：To address the high thermal load and wide temperature range requirements of heavy-duty trucks， this study proposes an R290 integrated thermal-management system. Through graded refrigerant charge and comparisons of four configurations， the optimal charge amount and preferred configuration are determined. The results indicate that the optimal charge amounts for the passenger compartment cooling and heating modes are 400-580 and 470-590 g， respectively， while the optimal charge amount for the battery rapid cooling is 530-560 g. Under cooling conditions， the dual-system air-cooled configuration shows the best performance， achieving a cooling capacity of 14.8 kW while driving and a cooling capacity of 24.0 kW while parked at 40 ℃， thereby fully satisfying high-temperature requirements. Under heating conditions， the single-system water-cooled/120 mL configuration shows the best performance， achieving a heating capacity of 27.0 kW while driving and of a heating capacity of 14.7 kW while parked at -30 ℃； combined with PTC （positive temperature coefficient） assistance， it can fulfill the extreme low-temperature requirements. In summary， the dual-system air-cooled configuration is recommended for hot regions， while the single-system water-cooled/120 mL configuration is recommended for cold regions. This study provides the experimental evidence for the design of R290 thermal-management systems in heavy-duty trucks.关键词：R290;heavy-duty trucks;charge amount;system configuration1|0|0更新时间：2026-09-14
- 摘要：SignificanceOptical cryocoolers are cryogenic refrigeration devices based on anti-Stokes fluorescence. They feature vibration-free operation without moving parts， freedom from electromagnetic interference， and a compact architecture. With the increasing demand for low-vibration and highly reliable cryogenic cooling in space infrared detection， optical clocks， precision time-frequency metrologies， and deep-space science missions， optical cryocoolers show a significant potential for future applications in space payloads， precision measurements， and low-noise detections.ProgressThis study reviews the development of optical cryocoolers from the perspectives of basic principles and emerging physical mechanisms of solid-state optical refrigeration， optical refrigeration material systems， pump absorption enhancement， thermal management， and system integration. In terms of materials， the developments of Yb3+-doped fluoride glasses and crystals， long-wavelength rare-earth-ion-doped materials based on Er3+ and Tm3+/Ho3+， rare-earth-ion-codoped fluoride crystals and semiconductor materials are summarized. In terms of pump absorption enhancement， the operational characteristics and applicable conditions of non-resonant multipass cavities and resonant cavities are compared. In terms of the thermal management， the effects of thermal-link materials， structural design， and bonding techniques on heat conduction， fluorescence isolation， and cryogenic reliability are analyzed. Regarding system integration， the development from cooling the optical refrigeration material itself to cooling external payload， as well as approaches such as parallel multi-crystal configurations for enhancing the system cooling capacity， are reviewed， and the limitations imposed by the low cooling power of the refrigeration crystal and large system-level parasitic heat loads on the effective cooling power delivered to the payload are summarized.ConclusionsThe exploration of emerging physical mechanisms provides new pathways for solid-state optical refrigeration. Yb3+-doped fluoride crystals remain the most mature material system for cryogenic optical refrigeration. Non-resonant multipass cavities and resonant cavities can effectively improve pump absorption at cryogenic temperatures， while thermal management strategies provide the key methods of transferring cooling power from the refrigeration crystal to an external payload. Based on this， optical cryocoolers have progressed from cooling the refrigeration material itself to cooling external payload， and proof-of-concept prototypes have been demonstrated. The vibration-free nature of optical refrigeration also offers potential for silicon ultrastable reference cavities in optical-clock systems， solid-state nuclear clocks， infrared detections and imagings， and optically levitated precision measurements. However， owing to the limited cooling power of the refrigeration crystal and parasitic heat loads arising from thermal radiation， support conduction， fluorescence absorption， and interfacial thermal resistance， the effective cooling power delivered to the payload remains low， which is a major limitation for further applications.Prospects The future development of optical cryocoolers requires coordinated improvements in material performance， pump absorption at cryogenic temperatures， and a system-level thermal management. Increasing the cooling power of the refrigeration crystal， reducing parasitic heat loads， and optimizing thermal management strategies are expected to enhance effective payload cooling and promote engineering applications in infrared detection， optical clocks， and space science missions.关键词：optical cryocoolers;optical refrigeration material systems;pump absorption enhancement;thermal management;system integration1|0|0更新时间：2026-09-14
- 摘要：This study proposes a fast-charging and cooling strategy suitable for charging electric vehicles under high ambient temperatures. By jointly regulating the charging current based on cell temperature and state of charge （SOC）， this strategy aims to maximize the charging capacity of cells. A 1P108S battery pack composed of lithium-ion cells with a rated capacity of 119 Ah was used， and the heat generation model for the cell was established through Hybrid Pulse Power Characterization （HPPC） testing. During the charging process， the cooling system was utilized to mitigate battery temperature rise， and the effects of different cooling strategies on charging performance were systematically analyzed. The results indicate that the liquid cooling system achieved optimal heat transfer efficiency when the coolant flow rate was 12 L/min and coolant temperature was 22 ℃. To prevent the cells from overheating， the charging rate was limited when the cell temperature reached 48 ℃. Under the optimized strategy， the maximum battery temperature was 49.2 ℃ and charging duration was 2 654 s. Finally， the numerical model was validated through battery pack charging experiments， with deviations in the maximum temperature and maximum temperature difference both within 5%.关键词：battery thermal management;fast charging strategy;cooling strategy;heat transfer efficiency1|0|0更新时间：2026-09-14
- 摘要：To address high heat-flux dissipation and ensure uniform flow distribution across multiple heat sources， a multiscale heat sink integrating centimeter-， millimeter-， and micro-scale channels is designed in this study. The ANSYS Icepak thermal simulation software is used to analyze the effects of varying rectangular cross-sectional heights and widths on flow-distribution uniformity and system pressure drop under a specified liquid flow rate. Optimal geometric parameters obtained from numerical analysis are applied to fabricate the multiscale heat-sink prototypes， which are subsequently subject to performance testing and comprehensive analysis. Additionally， a simple and efficient method is designed to test flow-distribution uniformity. Results show that， for identical multiscale heat sinks， flow-distribution uniformity correlates positively with the liquid-supply flow rate. Specifically， when the flow rate is reduced to 83% of the rated value， the maximum difference of pressure drop remains below 3.5%； at a 67% reduction， this difference remains under 5%. In liquid-cooling heat-sink configurations， radiative heat transfer accounts for only a minor proportion of the total heat dissipation， while almost 90% of the heat is removed by the working fluid. When the heat flux of the heat source is 33.2 W/cm2， the temperature difference between the heat source and inlet liquid is merely 2.4 ℃， which demonstrates the outstanding heat-transfer capability of the microchannel and the excellent heat-dissipation performance of the multiscale heat sink. The results and test data derived from this study may facilitate the optimal design of multiscale heat sinks.关键词：multiscale;heat sink;liquid cooling;microchannel;flow-distribution uniformity0|0|0更新时间：2026-09-11
- 摘要：ObjectivePrevious studies have demonstrated that gradient wick vapor chambers exhibit high temperature uniformity， low thermal resistance， and a high capillary limit. However， most reported vapor chambers with gradient wicks are fabricated from copper； they typically employ either a single gradient wick layer or a dual-section gradient structure connecting the condenser and evaporator sides. By contrast， aluminum vapor chambers incorporating two gradient wick layers are rarely investigated. In this study， an aluminum vapor chamber featuring two gradient wicks was fabricated to investigate its performance under specific operating conditions and varying wick gradient orientations. The findings provide a thermal-management reference for electronic devices in typical operating scenarios.MethodAluminum powder was used as the working material. A 2×2 factorial design was established based on the gradient orientations at the evaporator and condenser sections， and four aluminum vapor chambers with dual-gradient wicks were fabricated accordingly. A test platform was established for porosity， permeability， thermal resistance， and temperature uniformity characterizations. Meanwhile， Δp was introduced to quantify the gradient difference between the upper and lower wick structures.Results and DiscussionExperiments show that under general operating conditions， the vapor chamber C—featuring inward-decreasing pore sizes at the evaporator end and outward-increasing pore sizes at the condenser end—exhibits excellent heat transfer and start-up performance. This is because the evaporator-end design directionally guides the working fluid backflow， thus reducing the risk of “dry-out”； additionally， the high permeability at the center of the condenser end accelerates heat exchange between the working-fluid vapor and condensate. At 80 W， vapor chamber C achieved the fastest start-up response time of 385 s. Compared with the start-up response time of 657 s for a nongradient vapor chamber， the structure of vapor chamber C enables more efficient working fluid circulation， thus accelerating start-up. Under pulsed operating conditions， thermal accumulation is governed by the structure. As the number of pulses increases， thermal accumulation decreases rapidly， with the reduction rate positively correlated with the pulse period. Under pulse periods of 360， 600， 960， and 1200 s， thermal accumulation during the third pulse decreased by 57.70%， 72.85%， 78.77%， and 82.21% compared with that during the first pulse， respectively.ConclusionsVapor chamber C—featuring inward-decreasing pore sizes at the evaporator end and outward-increasing pore sizes at the condenser end—exhibited optimal temperature uniformity. Compared with a non-gradient vapor chamber， the in-plane temperature differences at both ends of vapor chamber C were 24.02% and 26.07% lower. Δp values confirmed that an optimized gradient structure significantly enhanced the vapor chamber performance. For vapor chamber C （Δp>0）， the graded structure successfully balanced the capillary driving force and viscous pressure drop. Under high power （80 W）， vapor chamber C attained a minimum thermal resistance of 0.11 ℃/W and the shortest start-up response time of 385 s. Under pulsed loading， the temperature drop at low power was almost unaffected by the structure but increased with the pulse period. As the pulse period increased from 360 to 1200 s， the temperature drop increased from 57.70% to 82.21%.关键词：aluminum;gradient pore-size wick;pulsed loading;thermal accumulation1|0|0更新时间：2026-09-11
- 摘要：ObjectiveThe development of new energy vehicles that use the lithium-ion batteries （LIBs） as the power source has brought into the prominence of thermal safety risks arising from high-rate chargings. The accumulation of excess heat inside the batteries results in the large temperature differences and induces the thermal runaway， thereby threatening the safety of electric vehicles. Given that the optimal operating temperature range of LIBs is 293.15-313.15 K， an efficient thermal management system is critical for ensuring the battery performance and safety. Accordingly， this study proposes a profiled spiral channel liquid cooling plate， inspired by the DNA double helix and intertwined vine structures， to meet the heat dissipation demand of 99 Ah prismatic LIBs with a 3C charging current， and evaluates its performance in obtaining an optimal charging scheme that balances the thermal and hydraulic performances.MethodsThe internal resistance and entropy coefficient of a 99 A·h prismatic LIB were measured， and a volumetric heat source model of the battery was constructed based on Bernardi’s heat generation theory. A three-factor four-level L₁₆（43） orthogonal experiment was designed to investigate the impacts of the length ratio， spiral angle， and width ratio on the maximum temperature， average surface temperature， and system pressure drop， and the optimal parameter integration was determined using the range analysis. For a consistent channel cross-sectional area， channel number， and inlet flow rate， the spiral channel was compared with three typical structures， i.e.， parallel， corrugated， and Tesla valve channels. The laminar flow was numerically simulated using ANSYS Fluent and verified with a grid independence study. Finally， the desirability function method was adopted to evaluate the thermal-hydraulic performance of each scheme quantitatively.Results and DiscussionThe range analysis results show that the spiral angle most affects the maximum and average surface temperatures， whereas the width ratio and system pressure drop are positively correlated. The optimal parameter integration is determined as a length ratio of 0.75， spiral angle of 160°， and width ratio of 0.85. Also， four types of channels show the distinct heat dissipation performances： the parallel channel delivers the worst cooling effect with a maximum LIB temperature of 319.22 K； the corrugated channel achieves a slightly improved performance； the Tesla valve channel reduces the maximum temperature to 312.92 K， owing to its distinctive flow-field characteristics； and the proposed spiral channel achieves an optimal temperature control performance， limiting the maximum temperature to 312.65 K. The inner-outer multiring structure of the proposed spiral channel extends the fluid flow path， optimizes the flow distribution， and improves the heat absorption efficiency of the coolant. In terms of the pressure drop， the parallel channel has the lowest flow resistance， whereas the spiral and Tesla valve channels exhibit the higher pressure drops owing to their complex structures. Per the desirability function calculation， the spiral channel has a desirability value of 0.086， and ranks the first in the heat dissipation among four structures.ConclusionsThe experimental internal resistance （1.17 mΩ） and entropy coefficient （-6.0×10-5 V/K） accurately characterize the heat generation of the 99 A·h LIB， thereby supporting the numerical simulations. The structural parameters of the spiral channel exert different degrees of influences on the thermal and hydraulic performances， and the optimized parameter integration can balance the temperature control and flow resistance. Compared with the three conventional liquid cooling channels， the proposed spiral channel exhibits superior heat dissipation， thus providing a new design guideline for structurally optimized liquid cooling plates in the thermal management systems of LIBs.关键词：battery cooling;spiral channel;plate heat exchanger;computational fluid dynamics simulation2|1|0更新时间：2026-09-11
- 摘要：ObjectiveIn arid regions， the low dew-point temperature of ambient air significantly limits the water-harvesting efficiency of conventional condensation-based atmospheric water-harvesting （AWH） systems. To address this limitation， this study proposes a desiccant-wheel-enhanced condensation AWH hybrid system that elevates the dew-point temperature of the incoming air prior to condensation， thereby enhancing the condensation potential. The primary objective of this study was to investigate the performance of three hybrid system configurations featuring different desiccant-wheel partition structures （WFS-1， WFS-2， and WFS-3） under various environmental and operational conditions as well as identify the optimal configuration and operating parameters for efficient water production in arid environments.MethodsA comprehensive mathematical model describing coupled heat and mass-transfer processes in a hybrid system was developed. The model integrates desiccant-wheel dehumidification and regeneration processes with the subsequent cooling condensation process. Numerical simulations were performed to evaluate the effects of key parameters on system performance， including the ambient humidity ratio， ambient temperature， regeneration temperature， and cooling-source temperature. Three system configurations—WFS-1， WFS-2， and WFS-3—were compared. Performance metrics included water harvesting rate （WHR， kg/h） and water harvesting efficiency （WHE， kg/（kW·h））. All simulations were conducted under steady-state assumptions， and model accuracy was validated against experimental data from the literature.Results and DiscussionThe simulation results revealed several key findings. First， the ambient humidity ratio showed a strong positive correlation with the water yield. When the humidity ratio exceeded 3 g/kg（dry air）， WFS-1 achieved the highest WHR owing to its lower pressure decrease and simpler heat-transfer characteristics. However， under extremely dry conditions （humidity ratio <3 g/kg（dry air））， WFS-3 outperformed the other two configurations owing to its enhanced moisture adsorption efficiency in low-humidity environments.ConclusionThis study demonstrated that integrating a desiccant wheel with condensation-based atmospheric water harvesting is a viable strategy for improving the water yield in arid regions. The hybrid system performance was highly sensitive to the ambient humidity ratio， and ambient， regeneration， and cold-source temperatures. Among the three configurations， WFS-1 is recommended for moderately humid arid conditions （humidity ratio >3 g/kg（dry air））， whereas WFS-3 performs better in extremely dry environments （humidity ratio <3 g/kg（dry air））， and offers superior energy efficiency under high-temperature regeneration conditions. These findings provide theoretical guidance for the design and optimization of energy-efficient atmospheric water-harvesting systems tailored to arid and semiarid regions.关键词：Atmospheric water harvesting;rotary dehumidification;condensation water harvesting;arid regions15|28|0更新时间：2026-09-09
- 摘要：This study develops and experimentally validates a three-dimensional unsteady numerical model of an automotive CO2 scroll compressor （theoretical displacement： 1.272 m³/h） to explore effects of internal leakage on compressor performance. The simulation errors remained within 7.8% of the experimental results. Using this model， the effects of axial clearance and sealing structures were investigated. The results show that the sealing structure significantly suppresses secondary gas heating and reduces the discharge temperature by preventing the leakage of the refrigerant from the high-pressure chamber to the discharge and adjacent working chambers. Under the same axial clearance， incorporating the sealing structure reduced the discharge temperature by 16% and improved the volumetric efficiency by 19.7%. Expanding the axial clearance from 0.01 to 0.03 mm increased the discharge temperature by 13% and reduced the volumetric efficiency by 13.7%， while alleviating the over-compression. Moreover， the seal groove depth significantly impacts the leakage， as the sealing structure changes the radial leakage path. Increasing the groove depth increases both the radial and tangential leakage rates， with the former increasing more sharply. The radial leakage constitutes approximately 80% of the total leakage in the compressor， and its proportion increases with the groove depth. Additionally， the elevated leakage raises the suction chamber pressure， and triggers a backflow at the suction inlet. These insights offer guidelines for leakage control and sealing optimization in CO2 scroll compressors.关键词：CO2 scroll compressor;leakage characteristics;numerical simulation;sealing structure4|3|0更新时间：2026-09-09
- 摘要：ObjectiveOil-free linear compressors employ a narrow clearance between piston and cylinder to achieve noncontact operation， thereby eliminating lubrication-related contamination and mechanical wear. However， the unavoidable clearance leakage reduces the volumetric efficiency and becomes increasingly severe under high-pressure conditions， thereby limiting overall compressor performance. Labyrinth seals have been widely adopted in turbomachinery and reciprocating compressors owing to their excellent leakage-suppression capability. Nevertheless， their application in oil-free linear compressors has rarely been reported， and the influence of cavity geometry on transient leakage characteristics has not been systematically clarified. In this study， a rectangular labyrinth seal was proposed for sealing the piston–cylinder clearance， and the effects of cavity geometry on sealing performance were investigated.MethodA transient computational fluid dynamics （CFD） model was established for an oil-free Oxford-type moving-magnet linear compressor. The numerical model incorporated the compression chamber， piston-cylinder radial clearance， rectangular labyrinth seal， and back chamber， enabling simulation of the transient leakage process throughout one operating cycle. Simulations were performed at pressure ratios of 2， 3， 4， 5， and 6. The characteristic cavity size was first evaluated by assigning identical values of 0.1， 0.2 and 0.4 mm to the cavity width， depth and spacing， respectively. Subsequently， the cavity width， depth， and spacing were varied independently， whereas the remaining parameters were maintained at their reference values. The sealing performance was evaluated using the instantaneous leakage mass-flow rate， net-leakage ratio， and transient pressure， velocity， and refrigerant density distributions. Finally， the optimized labyrinth seal was compared with a conventional smooth-clearance seal under identical operating conditions.Results and DiscussionCavity geometry significantly influenced transient-leakage characteristics. An optimum characteristic cavity size of 0.2 mm was obtained， corresponding to a net-leakage ratio of 0.798%. Independent parametric analyses further indicated that the optimum cavity dimensions were 0.2 mm width， 0.1 mm depth， and 0.2 mm spacing， yielding a minimum net-leakage ratio of 0.668%， which decreased progressively along the leakage path because of successive throttling through adjacent labyrinth cavities. Meanwhile， the refrigerant density exhibited a layered distribution that reversed with the leakage direction during different stages of the compression cycle. The transient velocity field showed that the local high-velocity regions were primarily concentrated within the throttling gaps between adjacent cavities， whereas the low-velocity recirculation zones were maintained inside the cavities throughout the cycle. Compared with the conventional smooth-clearance seal， the proposed labyrinth seal reduced the net-leakage ratio by 46.52% at a pressure ratio of 6. Moreover， leakage suppression became increasingly pronounced as the pressure ratio increased， demonstrating the superior sealing capability of the labyrinth configuration under high-pressure ratio conditions.ConclusionThe proposed rectangular labyrinth seal effectively suppressed clearance leakage while maintaining noncontact piston operation. An appropriate cavity geometry is essential for achieving high sealing performance. The optimized structure provided an effective sealing solution for oil-free linear compressors operating under high-pressure ratio conditions.关键词：valve-controlled linear compressor;labyrinth seal;clearance leakage;numerical simulation;sealing performance5|0|0更新时间：2026-08-20
- 摘要：Continuous deteriorations of thermal environments in subway tunnels induces long-term service problems， which significantly affect their safe and efficient operations. Energy tunnel technology is an effective solution for these problems. However， the existing research has not fully revealed the heat-transfer characteristics of shield-energy tunnels with capillary heat exchangers （CHE） under seepage conditions， thereby restricting the engineering application of this technology. Based on a demonstration project， this study established a three-dimensional thermal-seepage coupling numerical model of shield-subway-energy tunnels with CHE， and analyzed the influences of heat-exchanger operational parameters on the heat transfer performances of energy tunnels under seepage conditions. The results showed that seepage could significantly improve the heat-transfer performance of shield-energy tunnels. When the seepage velocity increased from 0 to 2.3×10-5 m/s， the heat transfer during the heating and cooling seasons increased by 106.77% and 276.00%， respectively. The heat transfer capacity of the CHE loop near the seepage inlet was slightly higher than that farther from the inlet. In addition， the inlet flow velocity and temperature of the CHE significantly affected the heat transfer performance. When the inlet flow velocity increased from 0.06 m/s to 0.12 m/s， the heat transfer capacities during the cooling and heating seasons increased by 89.53% and 72.66%， respectively. When the inlet temperature increases by 6 ℃ during the cooling season and decreased by 6 ℃ during the heating season， the heat transfer capacities increased by 58.80% and 177.01%， respectively. However， increasing the inlet flow velocity of the CHE and the heat-transfer temperature difference led to a decrease in the uniformity of the temperature distribution of the segments. This study provides a theoretical support for the design and application of shield-energy tunnels.关键词：energy tunnels;seepage;capillary heat exchanger;thermal performance;subway12|15|0更新时间：2026-08-20
- 摘要：To address the redundant drying time and over-drying problems of rule-based threshold strategies in heat pump clothes dryers， this paper proposes an automatic dryness judgment method based on multi-dimensional time series feature engineering and ensemble learning. The multi-dimensional time series features were extracted according to the operating characteristics of heat pump systems. By combining weakly supervised label generation with a dual sample-cleaning strategy involving label-purity filtering and out-of-fold prediction， an ensemble learning model integrating XGBoost， LightGBM， and CatBoost was established， and a dual-threshold confidence lock was further introduced to reduce the risk of false dry judgments. The results show that the proposed model achieved a test accuracy of 91.26% and F1 score of 92.17% on the static dataset， and the judgment accuracy of high-confidence samples increased to 96.30% after applying the confidence lock. In International Electrotechnical Commission-load and real-load validation tests， the drying time was reduced by 30.9% and 22.4%， respectively， compared with the rule-based threshold strategy while still satisfying the drying requirements. The proposed method can effectively alleviate redundant drying time and over-drying problems and shows good engineering application potential.关键词：heat pump clothes dryer;automatic dryness judgment;time series feature engineering;ensemble learning;confidence locking8|7|0更新时间：2026-08-17
- 摘要：To address the limited energy efficiency of the CO2 transcritical booster refrigeration system due to insufficient recovery of expansion work， this paper proposes a collaborative optimization scheme of multiple ejectors and parallel compression. An experimental system of a multi-ejector replacing the expansion valve and integrating parallel compressors was built， and the influence of parallel compression on system performance was compared under different ejector combinations. The results show that the liquid ejector plays a key role in the system performance， and the "one liquid ejector with three gas ejectors" mode yields the optimum system performance. Compared with the expansion valve system， the maximum refrigeration capacity and COP of the system without parallel compression increased by 8.4%-11.2% and 15.3%-18.8%， respectively. After the introduction of parallel compression， the maximum refrigeration capacity and COP increased by 0.5%-13.9% and 4.6%-17.7%， and the power consumption decreased by 3.3%-4.3%， providing an experimental basis for the efficient optimization of the CO2 booster refrigeration system.关键词：multiple ejector;transcritical CO2;booster system;parallel compression20|7|0更新时间：2026-08-17
- 摘要：To address the challenge of balancing the pressure-bearing capacity and high-efficiency heat exchanging in emerging solid-state barocaloric refrigeration systems， the present study proposes a composite heat-exchanging structure featuring carbon fiber-wrapped finned tubes and establishes a simulation framework for barocaloric refrigeration systems. Using a highly thermally conductive barocaloric composite of co-crystal material NPG0.75-TMP0.25-20%EG， a simulation framework for barocaloric refrigeration was developed based on a finite element model of multi-physics fields， and the barocaloric phase transition state of the computed micro-element was characterized to solve the adiabatic temperature variation. Compared with a conventional aluminum alloy single tube， the composite finned heat exchange tube reduces the weight and structural heat capacity by 95%， increases the heat exchanging area by 2.5 times， and reduces the thermal resistance by 52%. This could significantly improve the heat exchange efficiency， weaken the negative impact of structural heat capacity on temperature changes， and accelerate the system to reach a steady state. Further investigations into the effects of cycle duration， flow velocity of heat exchange fluid， and operational temperature range reveal that the optimal system coefficient of performance （COP） is achieved under a 10-s cycle period and fluid flow velocity of 0.5 m/s. This research provides the theoretical guidance for heat-exchanger structural design with the enhanced overall mechano-thermal performance and operational optimization of solid-state barocaloric refrigeration systems.关键词：barocaloric refrigeration;multi-physics field simulation;carbon fiber reinforcement;plastic crystal composite12|6|0更新时间：2026-08-17
- 摘要：Electric motors are developing towards high power density and miniaturization， making thermal management increasingly critical. This study investigated the influence mechanisms of key parameters， such as the heat source power， position between evaporator and condenser side， and bending angle， on the heat transfer performance of heat pipe. Moreover， comparative analyses were performed on the prediction performance of five machine learning models： genetic algorithm optimized back propagation neural network （GA-BPNN）， convolutional neural network （CNN）， least squares support vector machine （LSSVM）， random forest （RF）， and extreme gradient boosting （XGBoost）. The results indicate that： the coupled detrimental effects of gravity and bending angle on the capillary wick structure govern the heat transfer performance； under a 90° bending angle at 60-W heat source power， the side arrangement of the condenser above evaporator achieves the best equivalent thermal conductivity， which is 30 times that of the condenser under evaporator. The mean absolute percentage error of XGBoost is 3.72%， coefficient of determination is 0.95， root mean square error only higher than that of the GA-BPNN model， and training time is less than 2 s， demonstrating the best performance among five models. The prediction results of XGBoost model illustrate that different positions and bending angles lead to different dissipation performances. To improve the temperature uniformity in the winding of motor， a heat pipe with 0° bending angle is recommended for the heat dissipation of motor.关键词：motor;heat pipe;equivalent thermal conductivity;machine learning13|8|0更新时间：2026-08-17
- 摘要：With the rapid development of artificial intelligence and high-performance computing， cold-plate liquid cooling technology has gradually become a mainstream solution for satisfying the heat-dissipation demands of high-heat fluxes data centers. This paper describes the triggering mechanisms， impact hazards， and the coupled evolution patterns of typical faults in data center cold-plate liquid cooling systems. The principles and characteristics of direct-detection techniques and inverse-problem fault diagnosis techniques are then summarised based on operational data and outlines the key problems encountered when applying these diagnostic techniques to real-world cold-plate liquid cooling systems. Finally， based on diagnostic experience in the HVAC （heating， ventilation and air conditioning） field， this study concludes the targeted methods for addressing these problems， including semi-supervised learning， few-shot learning， data augmentation， and physics-data fusion. Future research could focus on multi-algorithm fusion， mitigating data imbalance， and enhancing model interpretability and anti-interference capabilities to improve the accuracy， reliability， and engineering applicability of fault identification. The review and synthesis presented in this paper can serve as a reference for both theoretical research and engineering applications in the field of cold-plate liquid-cooling fault diagnosis.关键词：data centers;cold-plate liquid cooling;direct detection;fault diagnosis;machine learning48|21|0更新时间：2026-08-10
- 摘要：Linear compressors eliminate the slider-crank mechanism and facilitate oil-free operations. Self-lubricating opposed-piston linear compressors are suitable for integration into attitude-following heat-pump systems while significantly enhancing the system flow rate. In this study， a dual-motor self-lubricating opposed-piston linear compressor prototype was developed， and a comprehensive test bench was established. Using the R1234yf refrigerant， variable-capacity experiments were conducted to analyze the dynamic responses under series and parallel power supply modes. The results indicate that parallel drive requires a lower voltage than series mode， reducing the voltage differential required to achieve synchronized piston strokes in opposing configurations. During 62 Hz operation， when the supply voltage increased from 120 to 160 V， the series mode maintained， on average， a 0.17 higher power factor and 8.1% greater motor efficiency compared with the parallel mode. Thus， the driving mode selection should consider the specific application requirements.关键词：linear compressor;opposed-piston operation;oil-free lubrication;power supply configuration;dynamic characteristics27|12|0更新时间：2026-08-04
- 摘要：A front-jet-assisted cooling scheme is proposed for single-phase immersion oil-cooled servers to address severe bypass flows， insufficient effective flows inside heat sink channels， and local hotspots. Numerical simulations were performed to investigate the associated flow redistribution and mechanisms for heat-transfer enhancement. The results show that introducing front jets enhanced the coolant momentum and renewal at the heat sink channel entrance through local impingement， stagnation pressurization， and entrainment. In addition， the jet flow ratio primarily governed the enhancement intensity， whereas the number of jet holes assigned to each GPU heat sink primarily affected the coverage range and temperature uniformity. Comprehensive comparison indicates that the case with five jet holes and a jet ratio of 0.8 demonstrated the best overall performance， reducing the maximum GPU temperature from 99.12 ℃ to 82.10 ℃ and the temperature standard deviation from 2.54 ℃ to 0.26 ℃.关键词：single-phase immersion oil cooling;jet assistance;heatsink;flow distribution18|42|0更新时间：2026-07-30
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