Experimental Investigation on Cooling/Heating Characteristics of Ultra-Thin Micro Heat Pipe for Electric Vehicle Battery Thermal Management

Due to the heat pipes’ transient conduction,phase change and fluid dynamics during cooling/heating with high frequency charging/discharging of batteries,it is crucial to investigate in depth the experimental dynamic thermal characteristics in such complex heat transfer processes for more accurate thermal analysis and design of a BTMS. In this paper,the use of ultra?thin micro heat pipe(UMHP) for thermal management of a lithium?ion battery pack in EVs is explored by experiments to reveal the cooling/heating characteristics of the UMHP pack. The cooling performance is evaluated under di erent constant discharging and transient heat inputs conditions. And the heating e ciency is assessed under several sub?zero temperatures through heating films with/without UMHPs. Results show that the pro?posed UMHP BTMS with forced convection can keep the maximum temperature of the pack below 40 °C under 1 ~ 3 C discharging,and e ectively reduced the instant temperature increases and minimize the temperature fluctuation of the pack during transient federal urban driving schedule(FUDS) road conditions. Experimental data also indicate that heating films stuck on the fins of UMHPs brought about adequate high heating e ciency comparing with that stuck on the surface of cells under the same heating power,but has more convenient maintenance and less cost for the BTMS. The experimental dynamic temperature characteristics of UMHP which is found to be a high?e cient and low?energy consumption cooling/heating method for BTMSs,can be performed to guide thermal analysis and optimiza?tion of heat pipe BTMSs.

Sintering technology for micro heat pipe with sintered wick

In order to study reasonable sintering technological parameters and appropriate copper powder size range of micro heat pipe (MHP) with the sintered wick, the forming principle of copper powders in wicks and MHP's heat transfer capabilities were first analyzed, then copper powders with different cell sizes and dispersions were sintered in RXL-12-11 resistance furnace under the protection of the hydrogen at different sintering temperatures for different durations of sintering time, and finally the sintered wicks' scanning electron microscope (SEM) images and their heat transfer capabilities were analyzed. The results indicate that the wick sintered with copper powders of larger cell size or smaller size range has better sintering properties and larger heat transfer capabilities; and that the increase of either sintering temperatures or sintering time also helps to improve the wick's sintering properties and heat transfer capabilities, and the former affects more obviously than the latter. Considering both its manufacturing cost and performance requirements, it is recommended that copper powders with the size range of 140-170 μm are sintered at 900-950℃ for 30-60 min in practical manufacturing. In addition, two approaches to improve wick's porosity are also proposed through theoretical analysis, which suggests that the larger the wick's porosity, the better the heat transfer capabilities of the MHP.

Capillary force of a novel skew-grooved wick structure for micro heat pipes

In order to improve the capillary force of grooved wick, a novel skew-grooved wick structure was proposed for micro heat pipes. Risen meniscus experiments were carried out to research the capillary force of the skew-grooved and rectangle-grooved wick and a comparison of capillarity between the two wick structures was explored. A theoretical capillary force model of skew-grooved wick structure was also developed to calculate its effective capillary radius by comparing with the rectangle-grooved wick. From the experimental results, the maximum capillary force of the skewed-grooved wick is 8.62% larger than that of the rectangle-grooved wick. From the theoretical analysis, because the skewed-grooved wick has a smaller effective capillary radius, its maximum capillary force is 8.64% larger than that of the rectangle-grooved wick. The results indicate that the skew-grooved wick provides larger capillary force than the rectangle-grooved wick.

Experimental Investigation of Solar Panel Cooling by a Novel Micro Heat Pipe Array

A novel micro heat pipe array was used in solar panel cooling. Both of air-cooling and water-cooling conditions under nature convection condition were investigated in this paper. Compared with the ordinary solar panel, the maximum difference of the photoelectric conversion efficiency is 2.6%, the temperature reduces maximally by 4.7℃, the output power increases maximally by 8.4% for the solar panel with heat pipe using air-cooling, when the daily radiation value is 26.3 MJ. Compared with the solar panel with heat pipe using air-cooling, the maximum difference of the photoelectric conversion efficiency is 3%, the temperature reduces maximally by 8℃, the output power increases maximally by 13.9% for the solar panel with heat pipe using water-cooling, when the daily radiation value is 21.9 MJ.

Metal flow hysteresis behavior and shape control strategy during porthole die extrusion of micro heat pipe

The shape control strategy of micro grooves is still unclear and challenging during the porthole die extrusion of grooved micro heat pipe(MHP).Through the simulation and experiment of porthole die extrusion of a MHP profile,the metal flow hysteresis behavior within micro features and the effect of ram speed and extrusion temperature on it and the resulting forming integrity was elucidated.Innovatively,Taguchi design and variance analysis(ANOVA)were introduced to determine their influence magnitude on the metal flow uniformity calculated by simulation results.The main findings are given below.The metal flow hysteresis derives from part feature size effect.The negligible friction-affected area during conventional extrusion severely slows down the metal flow within micro features during the MHP profile extrusion,which is due to the surge in the area ratio of the friction-affected area to the region in which it is located.Neither ram speed nor extrusion temperature can change the distribution of the friction-affected area.However,increasing ram speed multiplies the metal flow hysteresis and severely reduces the forming integrity,whereas extrusion temperature has little effect.Following this strategy,batch extrusion of the profile with microgrooved width of 0.27±0.02 mm was achieved in industrialized conditions.

Performance simulation and optimization of new radiant floor heating based on micro heat pipe array

This paper proposes two new radiant floor heating structures based on micro heat pipe array(MHPA),namely cement-tile floor and keel-wood floor.The numerical models for these different floor structures are established and verified by experiments.The temperature distribution and heat transfer process of each part are comprehensively obtained,and the structure is optimized.The results show that the cement-tile floor has the better heat transfer performance of the two.When under the same inlet water temperature and flow rate,the keel-wood floor's surface temperature distribution is about 2℃ lower than that of the cement-tile floor.The inlet water temperature of cement-tile floor is about 10℃ lower than that of keel-wood structure when the floor surface temperature is the same.During a longitudinal heat transfer above MHPA,the floor surface temperature decreases by 0.5℃ for every 10 mm filling layer increase.In order to reduce the non-uniformity of the floor's surface temperature and improve the thermal comfort of the heated room,the optimal structure for a floor is given,with the maximum surface temperature difference reduced by 3.35℃.We used research focusing on new radiant floor heating,with advantages including high efficiency heat transfer,low water supply temperature,simple waterway structure,low resistance and leakage risk,to provide theory and data to support the application of an effective radiant floor heating based on MHPA.

Numerical and Experimental Investigation on the Performance of Battery Thermal Management System Based on Micro Heat Pipe Array

Battery thermal management is very crucial for the safe and long-term operation of electric vehicles or hybrid electric vehicles.In this study,numerical simulation method is adopted to simulate the temperature field of Li-ion battery cell and module.It is proved that the maximum temperature and maximum temperature difference of battery cell and module increase with the increase of charge/discharge rate(C-rate)of the battery.For battery module,it can reach a maximum temperature of 61.1℃at a C-rate of 2 under natural convection condition with the ambient temperature of 20.0℃.A battery thermal management system based on micro heat pipe array(BTMS-MHPA)is deeply investigated.Experiments are conducted to compare the cooling effect on the battery module with different cooling methods,which include natural cooling,only MHPA,MHPA with fan.The maximum temperature of battery module which is cooled by MHPA with a fan is 43.4℃at a C-rate of 2,which is lower than that in the condition of natural cooling.Meanwhile,the maximum temperature difference was also greatly reduced by the application of MHPA cooling.The experimental results confirm that the feasibility and superiority of the BTMS-MHPA for guaranteeing the working temperature range and temperature uniformity of the battery.

Thermal Performance of a Micro Heat Pipe Array for Battery Thermal Management Under Special Vehicle-Operating Conditions

The thermal management of battery systems is critical for maintaining the energy storage capacity,life span,and thermal safety of batteries used in electric vehicles,because the operating temperature is a key factor affecting battery performance.Excessive temperature rises and large temperature differences accelerate the degradation rate of such batteries.Currently,the increasing demand for fast charging and special on-vehicle scenarios has increased the heat dissipation requirements of battery thermal management systems.To address this demand,this work proposes a novel micro heat pipe array(MHPA)for thermal management under a broadened research scope,including high heat generation rates,large tilt angles,mild vibration,and distributed heat generation conditions.The experimental results indicate that the temperature difference is maintained 3.44°C at a large heat generation of 50 W for a limited range of tilt angles.Furthermore,a mild vehicle vibra-tion condition was found to improve temperature uniformity by 3.3°C at a heat generation of 10 W.However,the use of distributed heat sources results in a temperature variation of 3.88°C,suggesting that the heat generation distribution needs to be considered in thermal analyses.Understanding the effects of these special battery-operating conditions on the MHPA could significantly contribute to the enhancement of heat transfer capability and temperature uniformity improvement of battery thermal management systems based on heat pipe technologies.This would facilitate the realization of meeting the higher requirements of future battery systems.

Experimental investigations on the heat transfer characteristics of micro heat pipe array applied to flat plate solar collector

This paper introduces a novel flat plate solar collector(FPC) using micro heat pipe array(MHPA) as a key element.To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array(MHPA-FPC),an indoor experiment for thermal transfer characteristic of MHPA applied to FPC was conducted by using an electrical heating film to simulate the solar radiation.Different cooling water flow rates,cooling water temperatures,slopes,and contact thermal resistances between the condenser of MHPA and the heat exchanger were tested at different heating powers.The experimental results indicate that MHPA-FPC exhibits the enhanced heat transfer capability with increased cooling water flow rate and temperature.Total thermal resistance has a maximum decline of approximately 10% when the flow rate increases from 180 to 360 L h 1 and 38% when the cooling water temperature increases from 20℃ to 40℃.When the inclination angle of MHPA-FPC exceeds 30°,the slope change has a negligible effect on the heat transfer performance of MHPA-FPC.In addition,contact thermal resistance significantly affects the heat transfer capability of MHPA-FPC.The total thermal resistances lowers to nearly half of the original level when contact material between the condenser of MHPA and the heat exchanger changes from conductive silicone to conductive grease.These results could provide useful information for the optimal design and operation of MHPA-FPC.

Forming method of axial micro grooves inside copper heat pipe

The high-speed oil-filled ball spinning and drawing process was put forward to manufacture the axially grooved heat pipe with highly efficient heat-transfer performance,and the forming mechanism of micro-grooves inside the pipe was investigated.The key factors influencing the configurations of micro-grooves were analyzed.When the spinning depth varies between 0.4 mm and 0.5 mm,drawing speed varies from 200 mm/min to 450 mm/min,rotary speed is beyond 6 000 r/min and working temperature is less than 50 ℃,the grooved tubes are formed with high quality and efficiency.The ball spinning process uses full oil-filling method to set up the steady dynamic oil-film that reduces the drawing force and improves the surface quality of grooved copper tube.

Effects of bending on heat transfer performance of axial micro-grooved heat pipe

Heat pipe is always bent in the typical application of electronic heat dissipation at high heat flux,which greatly affects its heat transfer performance. The capillary limit of heat transport in the bent micro-grooved heat pipes was analyzed in the vapor pressure drop,the liquid pressure drop and the interaction of the vapor with wick fluid. The bent heat pipes were fabricated and tested from the bending angle,the bending position and the bending radius. The results show that temperature difference and thermal resistance increase while the heat transfer capacity of the heat pipe decreases,with the increase of the bending angles and the bending position closer to the vapor section. However,the effects of bending radius can be ignored. The result agrees well with the predicted equations.

Analysis of Collapse in Flattening a Micro-grooved Heat Pipe by Lateral Compression

The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no other better method to solve this problem. A new method by heating the heat pipe is proposed to eliminate the collapse during the flattening process. The effectiveness of the proposed method is investigated through a theoretical model, a finite element（FE） analysis, and experimental method. Firstly, A theoretical model based on a deformation model of six plastic hinges and the Antoine equation of the working fluid is established to analyze the collapse of thin walls at different temperatures. Then, the FE simulation and experiments of flattening process at different temperatures are carried out and compared with theoretical model. Finally, the FE model is followed to study the loads of the plates at different temperatures and heights of flattened heat pipes. The results of the theoretical model conform to those of the FE simulation and experiments in the flattened zone. The collapse occurs at room temperature. As the temperature increases, the collapse decreases and finally disappears at approximately 130 ℃ for various heights of flattened heat pipes. The loads of the moving plate increase as the temperature increases. Thus, the reasonable temperature for eliminating the collapse and reducing the load is approximately 130℃. The advantage of the proposed method is that the collapse is reduced or eliminated by means of the thermal deformation characteristic of heat pipe itself instead of by external support. As a result, the heat transfer efficiency of heat pipe is raised.

Thermal performance of heat pipe with different micro-groove structures

Four kinds of micro heat pipe of trapezoidal groove wick structure with different numbers of grooves or aspect ratios were studied and compared about thermal transfer performances in order to optimize the manufacture of micro heat pipe with groove wick structure. The results show that these micro heat pipes have excellent performance in heat transfer; the equivalent thermal conductivity coefficient is two orders of magnitude compared with that of copper; the number and aspect ratio of grooves have a prominent effect on the performance of such thermal transfer. The optimum number of grooves is lower than 60 and the best aspect ratio is near to 1.5. The temperature and thermal transport rate are almost directly proportional relationship, but this relationship will be broken up suddenly when the critical heat flux is reached.

Experimental Investigation of Micro Heat Pipes of Different Cross-Sections Having Same Hydraulic Diameter

微热的效果尖叫(MHP ) 它的热表演上的剖面图和取向试验性地在这研究被调查。测试用五张不同剖面图被进行(圆形、半圆形、椭圆、半椭圆、矩形) 有 3 的一样的水力的直径的微热管子，公里在三个不同倾斜角度放了(0 °， 45 °， 90 °) ，在水被用作工作液体的地方。MHP 的蒸发器节被一个电的加热器加热，冷凝器节被水的循环在在 condenser 节和水夹克衫之间的环隙凉下来。在 MHP 的不同地点的温度用五个校准的 K 类型热电偶被测量。热供应用被一个精确电流计和一个伏特计测量的一个电压管理者被改变。当 MHP 被弄平，热性能趋于败坏，这被发现。因此在 MHP 的所有剖面图之中，圆形的以流动驱散由半椭圆、半圆形、椭圆、矩形的剖面图跟随了的热展出最好的热表演。而且，它的热转移能力也与它的倾斜角度减少减少。最后，关联被开发它在 +7% 以内盖住所有试验性的数据。

Heat Pipe for Aerospace Applications—An Overview

The paper presents an overview of heat pipes, especially those used in different space missions. Historical perspectives, principles of operations, types of heat pipes are discussed. Several factors have contributed to the science and technology of the present state-of-Art heat pipe leading to the development of loop heat pipes, micro and miniature heat pipes and micro loop heat pipes. The paper highlights the advancement of heat pipe for hypersonic cruise vehicles, loop heat pipes with higher conductance in 10 K range, heat pipe switches for temperature control of the spacecraft electronics.

一种月面微型热管堆电源概念设想

未来月球科研站建设及月面探测等任务需解决长期稳定能源及电力供给问题,受月面复杂环境影响,月面能源供给挑战极大。核反应堆电源具有长寿命、全天候、环境耐受力强等优势,是解决月面任务长期能源需求的理想选择,热管冷却型反应堆作为一种新型反应堆电源具有系统简单、结构紧凑、可靠性高等特点,且易于实现长寿命设计。针对目前月面能源问题,提出了采用500 W电功率月面微型热管堆电源供电的初步设想,并重点对其屏蔽设计及辐射防护问题进行了研究,提出了相关屏蔽设计方案及辐射防护措施。经过初步屏蔽设计研究,该电源可采用移动式、月面固定点位布置及浅坑式布置多种方式为月面用电设备供电,质量可约束在500 kg左右,轻质且微型,为科研站月面核反应堆电源屏蔽设计提供了思路。

U型平板微热管LED散热器散热性能分析

针对目前LED表面发热量较大,局部温度过高,而导致其使用寿命减少的问题,该研究以平板微热管为核心传热元件,与锯齿形翅片结合,设计了一种U型平板微热管散热器。采用试验和仿真模拟相结合的方法,对不同风速、翅片结构、翅高及翅间距等关键影响因素进行分析。结果表明:通过对比分析U型平板微热管在两种室外工况下各测点试验值和模拟值,散热稳定后温度的最大误差分别为4.2%和6.7%,验证了模型的可靠性。风速分别为0.5和3.0 m/s时,锯齿型翅片都具有良好的散热性能。当风速为3.0 m/s时,锯齿型翅片、W型翅片、直翅片散热器稳定后热源温度分别为34.3、35.5和39.1℃。为找到最佳工况和结构,进行了正交分析,当室外风速为3.5 m/s,锯齿型翅片翅高为12 mm,翅间距为8 mm时,U型热管具有较佳的散热性能。研究结果可为LED散热系统的设计提供数据参考和设计思路,拓宽LED光源的应用范围。

平板微热管阵列换热器的研究现状与展望

平板微热管阵列换热器作为一种高效的传热设备,在当前节能减排的背景下具有广阔的应用前景。本文主要针对平板微热管阵列换热器的优化研究应用现状进行总结分析,得出其传热性能主要影响因素有:平板微热管阵列的微槽尺寸、工质选择、充液率、倾斜角度及换热器的翅片结构尺寸、热流量、运行温度、流动特性等,这些都会对其产生性能影响。在上述性能影响因素当中,对于平板微热管阵列换热器翅片结构尺寸参数的优化研究相对来说仍然较少,需要进一步的重视和探究。

整体式微通道换热器的性能分析

为了提升整体式微通道换热器的整体性能,建立了整体式微通道换热器的稳态换热模型,研究了结构参数与运行参数对其的影响规律。整体式微通道换热器以R245fa为工作工质,并在实验验证模型准确性的基础上,利用该模型模拟研究了换热器风量和换热器热管间距对系统整体热阻和空气侧压降等参数的影响。研究结果表明,当微通道换热器的蒸发段风量为0.41 m^(3)/s、冷凝段风量为0.21 m^(3)/s时,换热器的系统整体热阻为0.0380 m^(2)·K/W;随着冷凝段和蒸发段循环风量的增加,微通道换热器空气侧的压降增加,整体热阻均降低;微通道换热器的整体热阻的下降趋势随着风量的增加而逐渐减弱,得出在本研究范围内,蒸发段风量取0.45 m^(3)/s、冷凝段风量取0.69 m^(3)/s为宜;随着整体式微通道换热器热管间距的增加,微通道换热器整体热阻呈上升趋势,微通道换热器在蒸发段空气侧的压降呈下降趋势。当换热器热管间距为6 mm时,微通道换热器综合性能达到最佳。研究结果对通信基站冷却设备设计及微通道换热器结构与控制参数优化设计提供了参考依据。

电场辅助镁锂合金超塑变形行为及其在微型热管成形中的应用

通过等通道转角挤压工艺制备了不同晶粒尺寸的LZ91镁锂合金,当挤压道次超过8道次后,晶粒尺寸基本不再细化。为了探究电场作用下LZ91镁锂合金的超塑变形行为,设计并制造了电场辅助超塑单向拉伸实验平台,提出了一种“递减式”恒压通电方案,开展了不同电压、初始应变速率和晶粒尺寸下的电场辅助单向拉伸实验。实验结果表明,随着电压的增大,电流的焦耳热效应增大,LZ91镁锂合金的真应力-真应变曲线逐渐呈现出稳态流变特征。所有电压下原始镁锂合金的伸长率差异不明显,最大差异仅为16%。相比于低电压时,在高电压下初始应变速率对LZ91镁锂合金超塑变形行为的影响更加显著。电场对细晶LZ91镁锂合金超塑变形行为影响较大,主要体现在降低超塑变形温度和提高伸长率。在获得电场作用下LZ91镁锂合金超塑性能的基础上,通过DEFORM-3D仿真软件对LZ91镁锂合金微型热管挤压成形工艺进行了设计与仿真,长度为5 mm的坯料仿真得到的微型热管长度为40 mm,微沟槽深度为0.25 mm,等效应变分布均匀,为微型热管电场辅助成形工艺提供了有益探索。