Thermal analysis of an innovative flat heat pipe radiator

An innovative flat heat pipe radiator was put forward,and it has the features of high efficiency of heat dissipation,compact construction,low thermal resistance,light weight,low cost,and anti-dust-deposition. The thermal analysis of the flat heat pipe radiator for cooling high-power light emitting diode (LED) array was conducted. The thermal characteristics of the flat heat pipe radiator under the different heat loads and incline angles were investigated experimentally in natural convection. An electro-thermal conversion method was used to measure the junction temperature of the LED chips. It is found that the integral temperature distribution of the flat heat pipe radiator is reasonable and uniform. The total thermal resistance of the flat heat pipe radiator varies in the range of 0.38-0.45 K/W. The junction temperatures of LED chips with the flat heat pipe radiator and with the aluminum board at the same forward current of 0.35 A are 52.5 and 75.2 oC,respectively.

Numerical Simulation of Heat Transfer Performance for Ultra-Thin Flat Heat Pipe

The heat transfer performance of ultra-thin flat heat pipes with#180 copper mesh wick was studied by numerical simulation for different heating powers.The length,width and height of the ultra-thin flat heat pipe are 80 mm,8.5 mm and 1 mm,respectively.The temperature distribution and flow characteristics of ultra-thin flat heat pipes were simulated by coupling porous media model and user-defined function(UDF)in FLUENT.To validate the accuracy of the numerical model,the simulation results of the ultra-thin flat heat pipe are compared with the experimental data in predicting the evaporation section temperature.The numerical model has good accuracy for the one-dimensional heat transfer method of ultra-thin flat heat pipes.The velocity,pressure drop of the wick and total temperature difference have the same variation trend.With the increase of heating power,the temperature difference of ultra-thin flat heat pipes increases,and the pressure drop and the liquid velocity in the wick also increase.

Development and Investigation of a Miniature Copper-Acetone Loop Heat Pipe with a Flat Evaporator

The paper presents the results of development and investigation of a copper miniature loop heat pipe (LHP) with acetone as a working fluid. The device was equipped with a flat evaporator measuring 80 × 42 × 7 mm and vapor and liquid lines with an outside diameter of 3 mm, whose lengths were 145 mm and 175 mm, respectively. The LHP was tested at heat loads from 5 W to 60 W, different orientations in the gravity field and heat-sink temperatures from -40°C to +50°C. It is shown that the LHP retains its efficiency at all testing conditions. It is also mentioned that at a heat-sink temperature of +50°C the device operates in the mode of constant conductivity in the whole range of heat loads, and in this case a minimum thermal resistance of the “heat source-heat sink” system equal to 0.16°C/W is achieved, which is independent of the LHP orientation in the gravity field.

Visual Study on Flow and Operational Characteristics of Flat Plate Closed Loop Pulsating Heat Pipes

This paper presents an experimental study including visualization on a flat plate closed loop pulsating heat pipes.It consists of a total of 40 channels with square cross section(2 mm×2 mm,165 mm long) machined directly on an aluminum plate(180 mm×120 mm×3 mm) covered by a transparent plate.The working fluid employed is ethanol.As a result,various flow patterns and their transitions are observed and found to be related to the fluid fill ratio,input heat load and the device orientation.Also the operational characteristics and working mechanism are discussed.

Parametric Influence on Thermal Performance of Flat Plate Closed Loop Pulsating Heat Pipes

This paper presents an experimental study on a flat plate closed loop pulsating heat pipes. It consisted of total 40 channels with square cross section(2×2 mm2, 165 mm long) machined directly on an aluminum plate(180×120×3 mm3), which was covered by a transparent plate. The working fluid employed was ethanol. As the results, the influence parameters of thermal performance were investigated, such as filling ratio, heat load and operational orientations etc. Filling ratio was found to be a critical parameter, and its effect was rather complicated. According to its values the PHP plate could have four distinct working zones with different operational characteristics and heat transfer performance. The effect of heat load on thermal performance was found to be positive, and in general, increasing the heat load would improve heat transfer performance. In order to analyze the effect of gravity on thermal performance, three different heat modes and total seven tilt angles were tested and compared. Successful operation at all orientations with respect to gravity was also achieved.

Investigation of Geometric Factors of Convex Platforms in the Flat Evaporator of Loop Heat Pipes

This paper investigated the influence of geometric factors of vapor groove structures on the performance of flat evaporator of a loop heat pipe system. COMSOL multiphysics software was employed to simulate the heat transfer in the evaporator with convex platforms of different shapes,sizes and area ratios(φ)between convex platforms and the heated surface. The maximum temperature and temperature distribution of each model were obtained. The results showed that the decrease of the size of platforms and the increase of φ can lower temperatures and improve temperature distribution homogeneity of the heated surface. Compared with circle and oval platforms,square platforms achieved lower temperature. The results also indicated that φ had the most significant impact on the performance of the evaporator.

基于平板热管技术的电子器件热管理研究进展

随着电子器件不断趋于小型化和高度集成化发展,电子器件功率过高引发的散热问题亟待解决。平板热管由于具有均温性好、散热效率高等优势已为许多大功率电子元器件的散热问题提供了有效的热管理解决方案。但面对如今越来越多元化的散热需求,开发适应新型电子设备散热需求的高效平板热管仍是当前研究的热点。基于此,在对平板热管工作原理及结构特点进行阐述的基础上,对平板热管的传热性能、影响传热性能的因素(毛细芯结构、腔体厚度、工质、充液率、倾角和热源)、强化平板热管传热性能的措施(不同润湿性表面和支撑柱结构等)及其在小型化电子设备、IGBT晶体管、LED和电池组等电子器件散热应用等方面进行了系统性综述,指出研究不同毛细芯结构与腔体厚度下平板热管内部流动传热特性、散热性能强化的机制和综合优化方法,以及如何在不同电子器件热管理需求下设计出空间适应性强而散热性能高效的平板热管等仍是当前平板热管有待进一步突破的关键技术,将为平板热管在电子器件散热领域的进一步深入研究与优化提供一定参考。

平板热管式锂离子电池热管理系统仿真分析研究

锂离子电池是航空混合电推进系统的关键子系统,本文针对基于平板热管的航空锂离子电池热管理方案进行设计与性能评估。针对一款锂离子电池模组进行建模与验证,初步设计平板热管方案并进行仿真分析;在原方案基础上,对平板热管散热翅片进行结构优化设计并开展了实验验证,结果表明:优化后的方案可提高系统对流换热量。以优化后的平板热管为基础,结合航空器高空巡航工况的环境温度,平板热管换热性能将得到进一步提升:电池平均温度可降低10.6℃,降幅达18.83%。与水冷方案相比,平板热管优化方案散热能力与之相当,系统减重30%、能耗降低约63%。

基于平板热管的高温质子交换膜燃料电池堆启动特性

高温质子交换膜燃料电池(HT-PEMFC)运行温度约160℃,较传统低温电池具有更佳的电化学反应动力学、更简单的水热管理和更高的CO耐受性等优势。但运行温度提高,如何实现HT-PEMFC的快速预热启动成为制约其应用推广的重要挑战之一。当前工作中,针对一个额定功率为500W的HT-PEMFC电堆,尝试利用一种平板热管(FHP)对该电堆进行预热启动。设计搭建了实验装置,从预热时间、温度分布、传热量分布等方面对这一方法进行评估。实验结果表明,提高加热功率可以显著缩短预热时间,500W时预热耗时3000s,1500W时则仅需980s;但同时也造成温度均匀性出现恶化,500W时竖直方向最大温差约28℃,1500W时该温差则达到了80℃。此外,水平方向的温差也随加热功率的提高而增加,且越靠近热源的区域越明显,最高达15.7℃,这无疑会加速质子交换膜的机械失效。实际中,应在不过多影响电池运行寿命的前提下,提高加热功率以缩短启动时间。

质子交换膜燃料电池的平板热管传热性能

为探究平板热管在电堆中的传热性能,针对电堆中的传热条件设计平板热管的传热性能测试实验。结果表明:平板热管瞬态响应灵敏,响应时间在100—260 s之间;加热功率增加时平板热管的温差增加,等效热阻下降,5—15 W时处于启动阶段,40—50 W时等效热阻低于0.1℃/W,温差<5℃;冷却风速增加,平板热管的温差和等效热阻都有所上升;工作倾角对平板热管的性能影响显著,逆重力的工作条件将使平板热管的性能恶化,在50 W的加热功率、-90°工作倾角下平板热管的等效热阻约为90°时的3倍。

高寒地区平板热管式太阳能集热系统热性能研究

基于呼和浩特地区高寒气候条件,搭建两组完全一致的平板热管式太阳能集热系统,通过实验对比分析太阳辐射强度、传热工质流量、集热板表面积尘等因素对集热器瞬时集热效率以及系统热性能的影响。结果表明,在同等外界条件下,集热器的集热效率随着工质流量的增加而增大,集热效率与太阳辐射强度变化趋势相近,随积尘密度的增加,集热板表面积尘导致系统的得热量减少,集热性能下降。

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。

倾角对平板型LHP 运行性能的影响

通过改变内部毛细芯结构达到改善环路热管性能、减小环路热管体积的目的,取消储液腔,将传统的长矩形蒸汽槽道更改为特斯拉阀形状,并且将蒸发器进出口设置在蒸发器两侧。研究该热管在不同倾角下的启动性能、运行特性。结果显示:相对于0°倾角运行,倾角的存在能够减少环路热管的启动时间,降低蒸发器温度,存在倾角的条件下启动特性差别不大。随着功率的增加,不同倾角的环路热管热阻减小,仅在倾角(10°以下)较低时有较大的热阻。随着倾角的增加,环路热管热阻随功率的变化无较大改变。

基于TEC和平板热管的LED散热器结构优化设计

LED结温对其寿命和光效具有显著影响。高效的热管理对保持LED的性能稳定非常重要。为了有效降低LED结温、满足散热需求及特定场所的应用需求,结合热电冷却器(TEC)和平板热管(FPHP)重新设计了散热器结构,利用响应面法构建了针对散热器参数的双目标函数,通过非支配排序遗传算法(NSGA-II)求得Pareto最优解。基于散热器结构的最优值对TEC电流进行单因素优化分析,结果表明,优化后的LED最高结温比不采用TEC时的LED最高结温降低了23.3%,充分证明了优化散热器结构的有效性。

蒸发冷凝长度比对不同微槽平板铝热管热性能的影响

为研究不同蒸发段和冷凝段长度比值对平板铝热管热性能的影响,通过实验分析了相同截面尺寸、相同填充工质、矩形微槽道和三角形微槽道的平板热管90°安装,以及采用连续递增的输入热流和冷凝段强制风冷换热时,9种不同比值对平板热管热性能的影响。研究结果表明:提出的平板微槽道热管蒸发段冷凝段长度比值对平板微槽道热管热性能的影响明显。优选的两种类型蒸发段冷凝段长度比值在0.8~1.25范围内,传热性能良好。对比不同微槽道的平板热管发现,同等条件下矩形微槽道平板热管的传热性能优于三角形微槽道平板热管,并提出蒸发段冷凝段长度比值的最佳值为1,建议应用设计中蒸发段冷凝段长度比值范围为0.8~1.0。研究结果可对平板微槽道热管应用系统的设计提供准确参考。

扁平热管和液冷复合锂电池热管理性能分析

汽车动力电池在充放电中会产生大量的热,这些热量如果不断积累会引发电池热失控。热管传热性能高,没有额外功耗。为了把锂电池的工作温度维持在最佳范围内,设计扁平热管和液冷结合的TMS(热管理系统)对电池进行散热。实验通过控制变量法研究2、3C放电速率和25、35℃的环境温度对TMS散热性能的影响,同时观察加快冷却液流速对TMS传热性能的影响。结果表明:基于扁平热管和液冷的TMS能将电池表面最高温度t_(max)控制在37℃内,相比自然对流降低了23.4℃,温差Δt均低于5℃。t_(max)和Δt均随着放电倍率的变大或环境温度的升高而变大,并且该TMS有最低超过81.74%的传热能力。表明扁平热管和液冷复合的TMS在高温和大电流下是可行且有效的。

超薄平板热管传热性能的实验研究

随着电子器件的集成度逐渐提高,超薄平板热管作为一种适用于受限空间的高效散热器受到关注。本文对厚度为0.27mm的超薄平板热管进行传热性能的测试,以传热温差、传热量、热阻、等效传热系数作为指标,系统性地研究了加热功率、冷却方式及重力影响下的传热特性。研究发现,重力对超薄平板热管传热性能有轻微影响,竖直状态下的最大散热量较水平状态提高5%~10%,水平较竖直-逆重力状态提高2%~10%。冷却方式对其传热性能影响较大。在较低功率时,相比于自然冷却,强制冷却能使电子元器件在较低温度工作,但造成热管冷热端温差及热阻都比自然冷却条件下大,在超过一定功率(1.2W左右)后,温差及热阻急剧增大,等效传热系数减小,传热效果不佳。

亲水改性超薄平板热管传热性能

高性能电子器件的发展需要厚度更薄、传热性能更高的传热装置。热管依靠内部工质相变潜热来传递热量,具有热导率高、均温效果好等特点,广泛应用于电子器件的散热。本文制作了厚度为0.6mm的超薄平板热管,热管壳体内部和铜丝网均作亲水改性处理,丝网加工出蒸汽通道来实现气液共面以降低流动阻力。搭建热管性能测试平台,在自然对流冷却条件下研究去离子水、乙醇两种工质和不同充液率对超薄平板热管传热性能的影响。结果表明:经过化学改性改善了管壳和铜丝网对去离子水的浸润性,同时提高了铜丝网的毛细力,亲水改性后去离子水热管热导率相比改性前提升了19.53%;两种工质填充的热管的最佳充液率都是1.0,在控制蒸发段最高温度小于80℃的情况下允许输入的最大功率为6W;去离子水填充的热管表现出更好的热性能。

非均匀加热工况高温平板热管的稳态性能研究

高温平板热管(热板)与板式燃料元件紧密贴合构成的堆芯具有结构紧凑、接触热阻小、可在多种工况下稳定运行的特征。为研究热板用于堆芯冷却的可行性,基于COMSOL软件建立了热板三维热-流-固耦合分析模型,与文献实验参考值比对,相对偏差在5%之内,证明了该模型方法的可行性和正确性;基于模型分析了一种干道式复合吸液芯结构的合理性,以及非均匀加热对平板热管稳态传热和力学性能的影响。研究表明,复合吸液芯通过改变液体回流路径,有效降低了流动阻力,使热板轴向高热流密度稳定传热;非均匀加热条件下,平板热管仍能保持良好的传热性能和均温性;非均匀加热会增大热板壳体的热应力,但不会超过材料的应力限值;平板热管满足堆芯冷却的基本需求。