Maximum Heat Transfer Capacity Research Articles

Analysis of geothermal heat recovery from abandoned coal mine water for clean heating and cooling: A case from Shandong, China

Exploiting heat from abandoned mine water using heat pumps is attracting increasing attention worldwide. China has a large number of abandoned coal mines, but there are few applications of geothermal heat recovery from mine water. Here, we report a new case from Shandong, North China. Based on actual geological and underground space structures, numerical analysis is performed to study the flow and heat transfer in the complex connection network among roadways. For given temperature differences on the source side, the underground heat transfer is greatly influenced by flow rates in roadways. Under the acceptable performances and long-term stability of heat pumps, the maximum heat transfer capacity of roadways reaches 697.3 kW at the flow rate of 100 m3/h, with the power per unit length of 151.3 W/m, indicating a promising heat recovery potential. When switching between the extraction and injection well, both fluid directions and the distribution of flow rates in roadways change obviously, thereby affecting the underground heat transfer. Besides dominant flow paths, there exist weak flow paths, which can be identified by numerical analysis, and necessary blocking can be applied to optimize the flow and heat transfer. Excessively long horizontal straight roadways for heat exchange should be avoided.

Sensitivity Analysis and Optimization of Heat Transfer Performance of Ultra-Thin Vapor Chamber With Composite Wick

Abstract An ultra-thin vapor chamber (VC) with the composite wick formed by four spiral woven meshes (SWMs) and a copper mesh was proposed to solve the heat dissipation problem in miniaturized electronic equipment because of its sufficient heat transfer capability under limited thickness. However, the influence factors on the thermal performance of the VC with composite wick are more than that of the VC with a single type of wick. In this study, in order to investigate the thermal performance of the VC with composite wick, a theoretical model was developed to calculate the maximum heat transfer capacity. Besides, a three-dimensional numerical model for the heat transfer characteristics was established, and the simulation results have a good match with the experimental results. The orthogonal test method was adopted to determine that both the width of the vapor channel (wv) and the thickness of the vapor channel (tv) have a significant effect on the maximum heat transfer capacity and thermal resistance, while the porosity of the mesh (εmesh) has a prominent effect on the maximum heat transfer capacity, but has little effect on the thermal resistance. Further optimization of the sensitive factors for VC heat transfer performance was achieved to enhance the maximum heat transfer capacity.

Numerical study on the characteristics of sodium heat pipes for space application at operation limits

Sodium heat pipes are important thermal conductive components in space nuclear power sources. They efficiently transfer heat within the range of 500–1000 °C by utilizing the latent heat of phase change. However, their maximum heat transfer capacity is limited by various factors. In this study, numerical simulations were conducted to investigate the operating conditions of sodium heat pipes when encountering different heat transfer limits, with a focus on analyzing the vapor–liquid distribution and axial temperature distribution in evaporator section. It is revealed that as reaching the heat transfer limits, sodium heat pipes exhibit wall temperature fluctuations in evaporator section. When encountering the viscous limit, liquid aggregation occurs within the wick, causing discontinuous flow. As reaching the sonic limit, a vapor blockage zone forms at the outlet of evaporator section, disrupting the flow circulation within heat pipe. For the entrainment limit, the liquid inside wick is carried away by vapor flow, reducing the amount of liquid involved in phase change cycle. As in the capillary limit, inadequate liquid reflux leads to thinner liquid layer, weakening the flow circulation. During the transition from the viscous limit to the sonic limit, no significant phenomena of phase distribution occur in the evaporator section. As the sonic limit and the entrainment limit act together, both vapor blockage and liquid entrainment occur, accompanied by liquid accumulation. The phenomena when the entrainment limit and the capillary limit act together differ from those occurring individually. The simulation results provide references for a deeper understanding of heat transfer limit mechanism and other operating characteristics.

Simulation of, Optimization of, and Experimentation with Small Heat Pipes Produced Using Selective Laser Melting Technology

With the development of microsatellite technology, the heat generated by onboard components is increasing, leading to a growing demand for improved thermal dissipation in small satellites. Metal powder additive manufacturing technology offers the possibility of customizing and miniaturizing heat pipes to meet the specific requirements of small satellites. This article introduces a small-scale heat pipe designed using selective laser melting (SLM) technology. The heat pipe’s material, structure, and internal working fluid were determined based on mission requirements. Subsequently, the SolidWorks 2021 software was used for heat pipe modeling, and the ANSYS 2021R2 finite element analysis software was employed to simulate the heat transfer performance of the designed heat pipe, confirming its feasibility. The heat pipe’s structure was optimized using multi-objective regression analysis, considering various structural parameters, such as the channel diameter, vapor chamber height, and narrow gap width. The simulation results demonstrate that the optimized heat pipe achieved a 10.5% reduction in thermal resistance and an 11.6% increase in equivalent thermal conductivity compared to the original heat pipe. Furthermore, compared to conventional metal heat-conducting rods, the optimized heat pipe showed a 38.5% decrease in thermal resistance and a 62.19% increase in equivalent thermal conductivity. The heat pipe was then fabricated using a 3D printer (EOS M280), and a vacuum experimental system was established to investigate its heat transfer characteristics. The experimental results show that the heat pipe operated most efficiently at a heating power of 20 W, reached its maximum heat transfer capacity at 22 W, and had an optimal fill ratio of 30%. These results highlight the excellent performance of the heat pipe and the promising application prospects for SLM technology in the field of small satellites.

Heat transfer enhancement of the ultra-thin flat heat pipe integrated with copper-fiber bundle wicks

The rapid size shrinkage and the increasing power of the chip made it increasingly challenging to dissipate the heat generated by electronics. Ultra-thin flat heat pipes possessed the characteristics of high thermal conductivity, slender shape, and absence of moving parts, making them an effective solution for heat dissipation in small spaces. In this paper, the composite wicks made by copper-fiber bundle were designed and fabricated. The heat transfer performance of the ultra-thin heat pipe was experimentally investigated with a focus on the effects of wick design. The weaving method used in the composited wick affected the thermal performance of the ultra-thin heat pipe. The results indicated that the wicks with heterostructure increased the maximum heat transfer capacity by 6 W when compared with the homogeneous structures. The single-layer copper mesh design resulted in a 13 W increase in maximum heat transfer capacity compared to the double-layer design.

Design and experimental validation of a high capacity loop heat pipe for avionics cooling

With the rapid development of modern aviation industry, the power of avionics has been increasing continuously, bringing great challenge to thermal management. As an efficient two-phase heat transfer device, loop heat pipe (LHP) holds great application potential in avionics cooling. To address the issue of inadequate heat transfer capability, a set of kW-class LHP was specially designed and experimentally validated considering the airborne environment. A detailed introduction covering the entire design process was presented, in which some targeted design criteria were provided. Ammonia was chosen as the optimal working fluid, and stainless steel envelope with a nickel wick was adopted. Experimental validation showed that, at a heat sink temperature of 20 ℃, the designed LHP could achieve a maximum heat transfer capacity of 1021 W, confirming the efficacy of the design method. The average heat flux at the evaporator could reach 12.04 W/cm2. The LHP exhibited a maximum and minimum thermal resistance of 0.16 and 0.054 ℃/W, respectively, achieved at heat loads of approximately 50 W and 600 W. The maximum temperature fluctuation at the center of the saddle surface was no more than ±1.40 ℃. A method for estimating the heat leak between the evaporator and the compensation chamber was also developed, and the maximum heat leak rate was calculated to be approximately 5.2%. Moreover, the designed LHP also manifested excellent startup performance and operation stability.

Experimental investigation of the thermal characteristics of a novel pure-metal-based flexible ultrathin vapour chamber

The rapid development of high-performance flexible electronics requires novel metal-based flexible ultrathin vapour chamber (FUTVC) with higher heat transfer capacity to meet their heat dissipation needs. Although many works on flexible vapour chambers have been published, there are few works on metal-based flexible vapour chambers. Therefore, in this paper, a novel pure-metal-based FUTVC was proposed. Three kinds of FUTVCs were fabricated by brazing process and laser welding process, which were cost-effective processes suitable for mass production. The effect of manufacturing process, test direction and bending condition on the heat transfer performance of FUTVC was clarified, and the thermal mechanism of the FUTVC under bending conditions was theoretically analyzed. Results indicated that both laser welding and brazing can effectively seal the FUTVC. Wick sintered on the cover plate can effectively improve the thermal performance of the FUTVC. The maximum heat transfer capacity of the FUTVC in gravity state, horizontal state and anti-gravity state were 19 W, 16 W and 14 W, respectively. Furthermore, the maximum heat transfer capacity of the FUTVC with bending of 15°, 30°, 60° and 90° were 11 W, 10 W, 9 W and 8 W, respectively. The maximum effective thermal conductivity of the FUTVC was over 26000 W/(m•K) in horizontal state and over 10000 W/(m•K) under different bending conditions, which were approximately 65 times and 25 times higher than that of pure copper, respectively. The proposed novel FUTVC is promising for solving the heat dissipation problem of high performance ultra-thin flexible electronics.

Numerical study on thermal and hydraulic performance of a stacked-plate jet-impingement/microchannel heat sink

This paper presents a stacked-plate jet impingement microchannel (SP-JIMC) heat sink with highly-dense micro-fins and numerically investigates the thermal and hydraulic performance with single-phase water as coolant. Comparative analysis with the parallel microchannel heat sink and the micro-gap heat sink indicates that the SP-JIMC can achieve a better cooling performance and improve the temperature uniformity. With the inlet water temperature of 300 K and flow rate of 1 L/min, SP-JIMC has a thermal resistance of 0.45 cm2⋅K/W and a pressure drop of 208.2 Pa, and the maximum temperature difference is 2.2 K under 100 W/cm2 over a span of 35 mm. When the flow rate is increased to 10 L/min, the thermal resistance decreases to 0.21 cm2⋅K/W, and the pressure drop increases to 5085.9 Pa. The heat transfer analysis shows the micro-fins dissipate 77.5 % with a flow rate of 1 L/min. As the flow rate increases to 10 L/min, the jet impingement heat transfer is enhanced and the percentage of heat transfer over micro-fins drops to 56.2 %. Parametric study is performed to investigate the influence of structural parameters on the heat transfer characteristics. The results show the thermal performance is improved by increasing jet length and separator thickness, and reducing separator gap. The lowest thermal resistance is achieved at a jet width of 0.35 mm when the combined effects of jet impingement and micro-fins reach the optimum situation. In order to further improve the thermal performance of SP-JIMC, dual-side micro-fins and convex/concave impinged surfaces are simulated. The results show that adding the micro-fins on the out-flow plate can increase the heat transfer percentage over fins by 9.4 % and reduce the thermal resistance to 0.39 cm2⋅K/W under a flow rate of 1 L/min. The maximum heat transfer capacity is achieved when the inlet flow rate 35 L/min under 300 W/cm2 heat flux, the average temperature of the heating surface is 349.5 K, the pressure drop is 55.1 kPa and the thermal resistance is 0.165 cm2⋅K/W.

Heat management system of electric vehicle based on heat pump and energy recovery of removable battery

In order to manage the air-conditioning thermal system, battery thermal system and motor thermal system in a unified manner, the author proposes a self-developed integrated thermal management system for electric vehicles to recover battery energy. Firstly, the problems in the development of electric vehicles and the importance of thermal management system are introduced, secondly, the self-developed thermal management system scheme and the principle of each part are analyzed, the experimental results of thermal system in enthalpy difference chamber are also introduced. The experimental results show that: Under the double evaporation system, when the compressor speed is 4500 rpm, the maximum COP is 2.46, and the maximum COP charge is 1180 g, the maximum heat transfer capacity is 4819 W (wind side heat transfer + water side heat transfer), the evaporation temperature is 5.35?C, the evaporation superheat is 9.5?C, the condensation temperature is 59.3?C, the undercooling degree is 10.4?C, the suction pressure is 280 kPa, and the exhaust pressure is 1694 kPa. In conclusion, the thermal management system has great energy saving effect, which ensures that the electric vehicle range will not be greatly attenuated under winter heating conditions, and meets the requirements of comfort.

Improving the thermal performance of thin vapor chamber by optimizing screen mesh wick structure

• Effect of mesh layer and mesh number on the thermal performance of TVCs are investigated. • Thermal performance of the singular mesh wicked TVCs is dependent on effective capillary radius and wick thickness. • Larger thickness and smaller effective capillary radius of mesh wick can enhance the thermal performance of TVCs with wick thickness below 0.12 mm. • The multilayer composite mesh wick can improve the thermal performance of TVCs with a 0.4 mm thick mesh wick. Due to the booming of portable electronic devices, thin vapor chambers (TVCs) have been used to effectively transfer high heat flux in narrow space. In this study, various-layer singular meshes and multilayer composite mesh whose thicknesses are below 0.4 mm are developed by electrical resistance welding. For improving the thermal performance of TVCs, the various-layer singular mesh wicked TVCs are investigated to reveal the effects of mesh layer (mesh thickness) and mesh number (effective capillary radius of pores) on the thermal performance of TVCs, and the multilayer composite mesh wicked TVC is also studied as a comparison. The results show that the thermal performance of various-layer singular mesh wicked TVCs is mainly dependent on effective capillary radius along height direction and mesh thickness. Among the mesh wicks whose thicknesses are below 0.12 mm, the mesh wick with a larger thickness and smaller effective capillary radius can enhance the thermal performance of TVCs. The multilayer composite mesh wick with larger pores on top of smaller pores can improve the thermal performance of TVCs with 0.4 mm-thick mesh wick. In addition, three-layer 350 in -1 singular mesh wicked TVC shows the best performance, the maximum heat transfer capacity is 240 W and the lowest thermal resistance is 0.115 K/W.

Stress analysis and thermal performance of ultra-thin heat pipes for compact electronics

The ultra-thin heat pipe (UTHP) has been established as a highly effective thermal control component for cooling electronics with large heat generation rate and limited space for cooling. However, UTHP has been severely limited in application because of buckling or breaking on the shell of UTHP during the flattening process. In this study, a series of high-accuracy UTHPs with a thickness of 0.38–0.47 mm were fabricated by the phase-change flattening process. An internal vapor pressure model of the heat pipe during flattening was constructed and the heat transfer performances of UTHPs under different working conditions were experimentally investigated. According to the internal vapor pressure model, the pipe wall stress after flattening was the first to reach the yield strength of the material, and the upper limit heating temperature of UTHPs decreased with the decrease of flattened thickness. The maximum heat transfer capacity decreased with the decreased flattened thickness. UTHP with a thickness of 0.47 mm has a maximum heat transfer capacity of 4.5 W and a minimum thermal resistance of 0.64 °C/W. Moreover, gravity appeared to impose minimal effects on the heat transfer performance of UTHPs and the heat transfer capabilities of the UTHPs fluctuated within ±0.5 W for different gravity orientations.

Experimental investigation on the thermal characteristics of ultrathin vapour chamber with in-plane bending

• Probing the effects of in-plane bending on the UTVCs. • Systematic exploration of the heat transfer mechanism behind the in-plane bending effects. • A model to predicting the maximum heat transfer capacity and thermal resistance with given in- plane bending conditions was established. Although many works have been published on designing ultrathin vapour chambers (UTVCs), but no one has analyzed the effect of in-plane bending on the thermal characteristics of UTVCs. However, UTVCs often need to be designed into in-plane bending shapes to meet the limited and strict application space in portable electronic devices. Therefore, this work makes grate efforts to ascertaining the effect of in-plane bending on the thermal characteristics of UTVCs with thicknesses below 0.6 mm. UTVCs with four bending angles (0°/45°/90°/135°) and three bending radii (R10/R15/R20) were fabricated based on brazing, and the effects of filling rate and bending on the thermal characteristics of UTVC were investigated. The results show that the optimal filling rate of UTVC was 100%, the large bending angle and small bending radius lead to the increase of evaporation temperature and thermal resistance. The maximum heat transfer capacity of UTVC decreases by more than 27% when the bending angle change from 0° to 135°. In addition, a model for predicting maximum heat transfer capacity and thermal resistance was developed. The variation trend of predicted value was the same as experimental value, and the minimum error less than 3%.

Novel hybrid structures to improve performance of miniature flat evaporator loop heat pipes for electronics cooling

• Two novel hybrid structures have been proposed to improve performance of miniature LHPs. • A new and simple fabrication process has been proposed for fabrication of hybrid structures. • Hybrid structures have high bond strength, over 100 kPa. • The maximum heat flux is around 7 times higher than that of other polymer heat pipes. Two miniature loop heat pipes (LHPs) with novel hybrid structures of evaporators are developed to cool electronic devices. These structures ensure good heat conduction between evaporators and heat sources and low heat leak from evaporators to compensation chambers through these cases. LHP 1 uses a polymer-glass hybrid structure while LHP 2 uses a polymer-stainless steel hybrid structure. Hydrophilic polytetrafluoroethylene membranes are used as wicks and the working fluid is pure water. The bond strength of these hybrid structures was evaluated quantitatively. Then the effect of hybrid structures on the LHP thermal performance was investigated by measuring temperature at each point. The maximum heat transfer capacity reached 9 W (4.5 W / c m 2 ) and 14 W (7.0 W / c m 2 ) while the thermal resistances were 4.8 K / W and 2.1 K / W for LHP 1 and LHP 2 respectively. Using the polymer-stainless steel structure, the maximum heat flux is around 7 times higher while the thermal resistance is smaller than the corresponding values of other polymer heat pipes.

Effect of spiral woven mesh liquid pumping action on the heat transfer performance of ultrathin vapour chamber

In this paper, ultrathin vapour chambers (UTVCs) with two kinds of wick, namely, NO.250 copper mesh + 1 spiral woven mesh (SWM) and NO.250 copper mesh, were fabricated by brazing process. Capillary rise rate experiment was carried out using infrared (IR) camera method to characterize capillary performance of wicks and verify the SWM liquid pumping action. Effect of filling rate and SWM liquid pumping action on the heat transfer performance of UTVC were studied experimentally, and a model to predict the capillary limit of UTVC was established. The results show that the average rising speed of composite wick increased by 38.89%. The optimal filling rate of composite wick UTVC and copper mesh wick UTVC were 100%, and the maximum heat transfer capacities were 6 W and 5 W, respectively. The heat transfer performance of UTVC was greatly improved by SWM liquid pumping action, the maximum heat transfer capacity of UTVC increased by 20%–60% under different filling rate. The error of growth rate caused by SWM liquid pump action between capillary limit Qcl and maximum heat transfer capacity Qmax is less than 5%.

Experimental study on thermal performance of a pulsating heat pipe using R1233zd(E) as working fluid

An experiment is conducted to explore the thermal characteristics of a fourth-generation environmental refrigerant R1233zd(E) as working fluid for pulsating heat pipes (PHPs). The influences of inner diameter in 1.0 mm, 1.5 mm, and 2.0 mm, filling ratio around 40–70% and gravity on start-up characteristics are also studied. The experimental results show that, when R1233zd(E) is used as working fluid, PHP with diameter over 1.5 mm has lower thermal resistance, which can be reduced to 0.1184 °C/W under the optimum filling ratio of 50–60%. Increasing filling ratio will improve the maximum heat transfer capacity of PHP with diameter of 1 mm. PHPs with high filling ratio at 70% can start vertically, however, its heat transfer performance deteriorates under horizontal mode. The maximum heat transfer capacity of 190 W is obtained in the 2.0 mm ID PHP at a filling ratio around 50%. Finally, based on total 180 groups of experimental data, an empirical correlation with relevancy of 95% is proposed to predict the thermal performance of vertical PHP with R1233zd(E), and supervise the application design of PHP.

Prediction and prevention of over-temperature risk of Li-ion power batteries based on the critical heat transfer coefficient and intervention time

• The critical heat transfer coefficient ( h cr ) is defined to indicate that the heat dissipation capability is equal to the heat generated by the battery. • A quantitative criterion ( h < h cr ) is proposed to predict the over-temperature risk of batteries. • The intervention time ( τ intv ) is specified as the time when the battery reaches the over-temperature threshold. • A response surface analysis is conducted to determine intervention methods to prevent over-temperature risk. In recent years, research on high-performance battery thermal management systems (BTMSs) has increased to improve the safety and reliability of electric vehicle (EV) batteries. However, some underlying concepts have not been clearly explained. For example, which conditions are considered safe, and what about not？ This study focuses on the prediction and prevention of battery over-temperature risk using the finite element method. The critical heat transfer coefficient ( h cr ) is proposed as a quantitative criterion for risk prediction since it provides sufficient information on the battery operation, such as the dynamic operating parameters and the battery’s safety temperature. The intervention time is specified, and intervention methods are suggested to prevent risky conditions. Three parameters were found to have a substantial impact on risk prevention, namely, the equivalent heat transfer coefficient ( h ), representing the maximum heat transfer capacity of the heat dissipation system, the ambient temperature ( T ab ), representing the coolant temperature of the heat dissipation system, and the discharge current rate ( C rate ), representing the current level during discharge. A response surface analysis was performed using the maximum operating temperature of the battery ( T max ) as the response variable and three influencing factors as the input variables. The results show that safety zones can be found for each of the three influencing factors. For example, for the case considered in this work, the optimum T ab is around 281.15 K and should not exceed 305.15 K; the C rate should be below under 5C and should never exceed 8C; h should be greater than 50 W·m −2 ·K −1 . Suggestions are provided for choosing risk prevention methods according to the response characteristics of T max . The proposed method provides a novel approach for the research and design of intelligent BTMSs.

Visualized-experimental investigation on a mini-diameter loop thermosyphon with a wide range of filling ratios

The mini-diameter loop thermosyphon, which has an excellent heat transfer performance with simple, compact structure and pump-free advantages, can effectively solve the problem of heat transfer under high heat load in a confined space. The mini-diameter loop thermosyphon exhibits different gas-liquid transport and heat transfer patterns than the conventional-diameter one due to various gas-liquid phase transformation properties and a strong friction force in the mini-diameter channel. Furthermore, data on the visual analysis of gas-liquid transport and heat transfer properties of the mini-diameter loop thermosyphon under various filling ratios is still lacking. In this paper, a visible experimental research on a mini-diameter loop thermosyphon (3 mm) in a wide filling ratio range(44% -97%) is undertaken. The maximal heat transfer capacity increases initially and subsequently falls with the filling ratio, according to the testing data. At a low filling ratio, the flow pattern changes as slug flow - churn flow - annular flow with the heat load increase, leading to a low loop thermal resistance, and dry out occurs at 185 W heat load under 50% filling ratio. The gas-liquid flow shifts to slug flow-geyser boiling-bubble flow at high filling ratios (73% and 82%), and the bubble departure diameter steadily decreases with increasing heat load. Consequently, the heat transfer performance (thermal resistance) has been enhanced, and the maximum heat transfer capacity has been increased to 280 W. Single-phase flow is plainly seen in the loop when the filling ratio reaches 91% or even 97%, thus reduced heat transfer capacity. Therefore, the high-filling-ratio mini-diameter loop thermosyphon is better for high-load heat dissipation. However, a low thermal resistance shows at the low filling ratio, but the heat load is also low. As a result, a loop thermosyphon with a low filling ratio should be selected for the low heat load situation.

Thermal performance of wickless and orientation independent thin vapor chambers with wettability patterned micro structure

The wettability patterned micro structure (WPMS) arrays by laser etching are proposed to enhance the thermal performance of wickless thin vapor chamber (TVC). The effects of filling ratio and inclination angle on the thermal performance of wickless TVC with WPMS are investigated, and the untreated bare wickless TVC is also studied as comparison. The results show that the wickless TVC with WPMS can work stably at filling ratio ranging from 19.0% to 42.8%, and the optimum filling ratio is 42.8%. The maximum heat transfer capacity is 190 W with the lowest thermal resistance of 0.146 K/W. Since WPMS is superhydrophilic, it can provide nucleate sites to promote early onset nucleate boiling and capillary pressure to enhance the liquid supply. Thus, the wickless TVC with WPMS shows 10.98% lower thermal resistance and 18.75% higher maximum heat transfer capacity than that of the untreated bare wickless TVC. In addition, the thermal performance of wickless TVC with WPMS is insensitive to the orientation of the TVC.

Effect of the passage area ratio of wick on an ultra-thin vapour chamber with a spiral woven mesh wick

• An ultra-thin vapour chamber with a spiral woven mesh wick is proposed. • The effect of the passage area ratio of wick and test direction on performance is investigated. • The optimum design of the passage area ratio for high heat transfer is provided. • The passage area ratio of wick is adjusted by changing the number of spiral woven meshes. The effect of passage area ratio of wick on the heat transfer performance of the ultra-thin (0.4 mm-thick) vapour chamber (UTVC) which fabricated by brazing bonding was experimentally investigated, the spiral woven mesh (SWM) was utilized as the wick structure and support for the steam chamber of UTVC. The passage area ratio of wick of UTVC was adjusted by changing the number of SWMs. The capillary limits of UTVCs with different passage area ratio of wick were analyzed theoretically. The effect of SWM number and test direction on the thermal performance of UTVCs was experimentally investigated. The results indicated that the maximum heat transport capacity of UTVC increased and then decreased with increasing SWM number. An appropriate SWM number was beneficial to enhance the UTVC’s thermal performance by increasing the vapour-liquid circulation efficiency during heat transfer. The maximum heat transfer capacity of UTVC with 3 SWMs under gravity test direction was 6 W, which was 2 times, 1.4 times, and 1.3 times that of UTVC with SWM number of 1, 2, 4, respectively. The maximum heat transfer capacity of UTVCs changed by less than 10% under different test directions. The optimum passage area ratio of wick of the experimental UTVC was 62.5%.

Research on low-temperature performance of plate-fin hydrogen preheater for a proton-exchange membrane fuel cell

ABSTRACT In order to improve the cold-start performance of the fuel cell vehicles, a rapid anode heating system is provided to enable the stack to quickly reach its optimal performance at low temperatures. In this study, a three-dimensional element model of plate-fin heat exchanger has been developed and used to study the effect of structural parameters of staggered fins on the hydrogen transport phenomena and heat transfer performance. A series of simulations were carried out to study the influence of different fin parameters on heat transfer performance. Good agreement is found by comparing the simulation values with the predicted values of the experimental correlation and the deviation is less than 10%. It is shown that fin length has the greatest impact on the thermal performance factor of the radiator, while the contribution of fin thickness is minimal. Experiments show that the maximum heat transfer capacity of the plate-fin heat exchanger reaches 900 W, and the performance of the stack is increased by about 15%. Through the sensitivity analysis of the structural parameters of the hydrogen preheater, the optimal parameter combination was obtained. This research provides guidance for the design of the preheater and plays an important role in improving the low-temperature durability of hydrogen fuel cell engines.