双层毛细芯对环路热管传热性能的实验分析

环路热管作为一种高效的相变传热装置,其性能与位于蒸发器和储液槽之间的毛细芯结构密切相关。为了更深入研究双层毛细芯对环路热管传热性能的影响,利用不同颗粒直径铜粉制备双层毛细芯,在毛细芯总厚度为5 mm的条件下,通过调整大粒径和小粒径层的相对厚度来改变毛细芯厚度比,对平板型蒸发器环路热管启动和变工况运行进行实验测试。实验结果表明:在同一工况下,不同厚度比的双层毛细芯启动特性存在显著差异,启动过程中出现小粒径层蒸发效率低引起的温度过冲和环路热管中气液两相流变化导致的温度振荡;同时存在一个较优的双铜层毛细芯厚度比,大粒径(180～280μm)铜层厚度为3 mm可提高蒸发效率,小粒径(56～71μm)铜层厚度为2 mm可提供足够毛细抽吸力保证环路热管稳定运行。搭载该厚度毛细芯的环路热管不仅启动速度快(125 s),而且总热阻和蒸发器壁面温度均最低,最大加热功率达到120 W(21.10 W/cm~2),对应热阻为0.17 K/W。     

不同加热功率下充液率对无芯环路热管性能的影响

设计了以铝为管材、丙酮为传热工质的无芯环路热管。其蒸发段采用加热带加热,冷凝段用风冷降温。热管依靠蒸发压头使工质循环,并依靠重力作用,使冷凝液回流到蒸发段。搭建试验台并研究了不同加热功率下充液率对无芯环路热管的传热温差、传热量、热效率、热阻和当量导热系数的影响。结果表明:加热功率为150.00 W、充液率为30%时,无芯环路热管的均温性最好;传热温差和热阻均最小,分别为6.75℃、0.045 K/W。传热量132.00 W、热效率0.88、当量导热系数168 125 W/(m·K),均达到最大值。所以,该无芯环路热管在本实验研究范围内的最佳工作条件为加热功率150.00 W、充液率30%。     

氨工质平板式环路热管的传热性能研究

为了解决平板式蒸发器环路热管面对高集成电子元器件在较长传热距离下的散热能力不足等问题,本文采用更大面积的毛细芯和蒸发器,研制了一个传热距离达到1.6m的氨-不锈钢环路热管系统并进行了大量实验.实验过程中,加热壁面温度控制在70℃以下.实验结果表明,在热沉温度为-10℃的情况下,该环路热管可以在2.5W到180 W的热负...     

平板型环路热管温度波动现象研究

环路热管(loop heat pipe,LHP)是一种靠蒸发器内毛细芯产生毛细力驱动回路运行,利用工质相变来传递热量的高效传热装置.研制了一套小型平板式蒸发器、风冷式冷凝器的环路热管(mLHP),mLHP的毛细芯为500目不锈钢丝网,工质为丙酮和甲醇.蒸发器、冷凝器以及所有管路均由紫铜制成.着重研究了平板型mLHP在不同热负荷条件下的温度波动特性.实验结果表明,平板式mLHP在某些热流密度区间容易发生温度波动;同时,重点研究了工质对mLHP系统温度波动的影响,并给出相应的合理解释.     

平板蒸发器环路热管启动及充灌率特性研究

结合环路热管系统的优点与太阳能的广泛利用前景,设计并搭建了以太阳能利用为背景的新型毛细芯平板蒸发器环路热管系统,采用泡沫镍为毛细芯、乙醇为工质,实验研究了系统的启动运行特性,以及不同的工质充灌率对环路热管系统性能的影响。结果显示,在实验条件下,环路热管热源功率在300~1 600 W时具有良好的启动运行特性,55%的充灌率为最佳充灌率,具有更短的启动时间,相对更低的蒸发器温度与热阻。     

不同加热方式下环路热管蒸发器可视化研究

针对环路热管内部工质相变及流动换热问题,设计了环路热管蒸发器中心通道可视化实验平台,研究了不同加热方式对热管内工质状态和传热特性的影响。结果表明：加热方式直接影响热管10W启动过程,双面加热启动速度最快。相同热载荷时,不同加热方式下环路热管热阻及蒸发器中心通道内液面高度和成核情况存在差异。10W - 40W热载荷时,随着热载荷的增大,三种加热方式的传热热阻均在减小。40W-50W热载荷时,顶部加热方式下的热管性能出现恶化,底部加热传热性能出现停滞,仅双面加热性能稳定并有提高趋势。随着热负荷的增加,蒸发器中心通道内气液界面升高、气泡的产生变得更加剧烈,蒸发器通过吸液芯向储液器的漏热量增加,进而影响环路热管的性能。     

回路热管的热力特性分析

对回路热管稳定运行的动力和热力特性进行了分析,指出整个循环要顺利完成,主毛细芯产生的毛细压差必须具备的条件以及换热条件.并进而在合理的简化和假设条件下,对该热管建立了热力分析数学模型.用简单的代数运算代替了复杂的微积分计算,在精确度要求不高时,能够简便快速的进行热力分析.应用所提模型和计算方法对两个给定的回路热管进行了热力分析,得出了关键节点的压力、温度,分析了工作温度、环境温度和毛细芯厚度等对回路热管传热性能的影响.     

碱金属热管传热特性的模拟与试验分析

对用于热管式太阳能接收器的碱金属热管建立网络模型,并进行传热性能试验,模拟结果分别与集总参数法、热传导模型、文献和试验结果相比,吻合较好。网络模型考虑输入功率、管壁和吸液芯的厚度和导热系数,以及冷凝段长度等影响因素,可快速预测热管在不同功率下的工作温度以及热管结构参数对传热性能的影响。模拟得到热管吸液芯的导热系数对热管性能影响较大,热管管壁厚度和吸液芯厚度对热管性能的影响较小。     

长距离环路热管传热性能实验研究

基于航空航天等领域对环路热管长距离传热的需求,设计制造了一套传热距离8.1m的圆柱型蒸发器环路热管,试验了不同加热功率、不同冷凝温度下该环路热管的启动和变工况运行性能,并对其热阻及最大传热能力进行了分析。研究结果表明：当其他条件一致、初始气液分布相同和不同时,加热功率由100W增大至160W后,本研究中的环路热管启动时间和启动温升均发生一定程度的下降;加热功率100W时,冷凝温度由10℃降低至-10℃使得环路热管启动时间增加,加热功率160W时,冷凝温度由10℃降至-10℃对环路热管的启动时间影响不大。在冷凝温度0℃下,该环路热管在100~500W范围内均能稳定运行,且200W时环路热管传热效率最高,传热温差最小,稳定运行温度最低;另外,由于系统传输距离较长,每个工况达到稳定所需要的时间也较长,分布于1000至3500S内。随着加热功率的增大,环路热管热阻先减小后逐渐增大,该环路热管传热热阻最大不超过0.09℃/W,最小为0.024℃/W;随着传热距离的增大,管路的热损失增加,总压降和热阻也变大。当传热距离基本相同时,蒸发器容积的大小、冷凝器的冷凝能力及气液管线的布置形状均在一定程度上影响环路热管的最大传热能力。     

重力热管内流动与传热的研究现况

一、概述 随着热管技术的发展及其应用的日益广泛,至今已有各种不同功能、不同结构形式的热管类别。重力热管(亦称“两相闭式热虹吸管”)是在地面应用中常见的一种无芯热管。这是一种高效能的传热元件,其结构如图1所示:它是由管壳和工作流体组成自下而上分为加热段、绝热段和凝结段。在抽成真空的管壳内注入工作流体,密封抽气口后,便制成重力热管。液体在加热段受热蒸发(或沸腾),产生的饱和蒸汽经过绝热段到达凝结段     

Parametric analysis of steady-state operation of a CLHP

Cryogenic loop heat pipes (CLHPs) possess high pumping capability and good heat transfer performance that are important for effective and efficient cryogenic heat transport with considerable applications in space and terrestrial surroundings. Built on a previous model developed for a conventional loop heat pipe (Bai et al. [21]), this paper establishes a steady-state mathematical model for a cryogenic loop heat pipe using nitrogen as the working fluid. The modeling results are benchmarked with an experimental study and good agreement is achieved. A parametric study of the effect of heat sink temperature, parasitic heat loss, adverse elevation and heat loads applied to the secondary evaporator on the performance of the CLHP is conducted. A number of interesting phenomena are revealed through the analysis such as CLHP working in the variable conductance zone and enhanced performance of the CLHP by switching on the secondary evaporator. The detailed temperature and pressure characteristics of the CLHP are also captured that provide guidance for the system design and optimization.     

Sorption heat pipe—a new thermal control device for space and ground application

Sorption heat pipe (SHP) combines the enhanced heat and mass transfer in conventional heat pipes with sorption phenomena in the sorbent bed. SHP consists of a sorbent system (adsorber/desorber and evaporator) at one end and a condenser + evaporator at the other end. It can be used as a cooler/heater and be cooled and heated as a heat pipe. SHP is suggested for space and ground application, because it is insensitive to some “g” acceleration. This device can be composed of a loop heat pipe (LHP), or capillary pumped loop (CPL) and a solid sorption cooler. The most essential feature is that LHP and SHP have the same evaporator, but are working alternatively out of phase. SHP can be applied as a cryogenic cooler, or as a fluid storage canister. When it is used for cryogenic thermal control of a spacecraft on the orbit (cold plate for infrared observation of the earth, or space), or efficient electronic components cooling device (lased diode), it is considered as a cooler. When it is applied as a cryogenic storage system, it insures the low pressure of cryogenic fluid inside the sorbent material at room temperature.     

Experimental study on a cryogenic loop heat pipe with high heat capacity

Cryogenic loop heat pipes (CLHPs) are efficient heat transfer devices based on two-phase flow. Loop heat pipes for room temperature applications have achieved satisfactory thermal control functions with the benefits of no mechanical moving part, vibration isolation, thermal insulation, long heat transport distance and so on. While there exist many problems for low temperature applications of loop heat pipes, such as limited heat transport capacity, which could not meet the increasing requirement of instrument heat dissipation. This paper presents an advanced CLHP operating at liquid-nitrogen temperature range. An improved condenser structure is introduced to the CLHP, which greatly reduces the flow resistance and increases the cooling capability of the condenser. Many experiments have been carried out on the CLHP prototype for performance test, and one set of the experimental results with a 3.2 MPa fill pressure at room temperature is presented in this paper. It is shown that the advanced CLHP prototype can be operated reliably with a high heat transfer capacity up to 41 W and a limited temperature difference of 6 K across a 0.48 m transport distance.     

A novel design and experimental study of a cryogenic loop heat pipe with high heat transfer capability

A cryogenic loop heat pipe (CLHP) has been developed for future aerospace applications at TIPC (Technical Institute of Physics and Chemistry). This article presents a novel design of a cryogenic loop heat pipe and corresponding test system. The CLHP studied in this work has demonstrated to be able to operate in liquid-nitrogen temperature range using nitrogen as working fluid and to transfer large amount of heat over long distance with very small temperature difference. This device has been tested at three different orientations with respect to the relative position of the liquid line and the vapor line. The experimental results show that the CLHP can have a heat transfer capability of up to 12 W under horizontal and adverse gravity orientations and up to 20 W in liquid-nitrogen temperature range under gravity-assisted orientation.     

Parametric analysis of loop heat pipe operation: a literature review

Loop heat pipes (LHPs) are heat transfer devices whose operating principle is based on the evaporation/condensation of a working fluid, and which use the capillary pumping forces to ensure the fluid circulation. Their major advantages as compared to heat pipes are an ability to operate against gravity and a greater maximum heat transport capability. In this paper, a literature review is carried out in order to investigate how various parameters affect the LHP operational characteristics. This review is based on the most recent published experimental and theoretical studies. After a reminder of the LHP operating principle and thermodynamic cycle, their operating limits are described. The LHP thermal resistance and maximum heat transfer capability are affected by the choice of the working fluid, the fill charge ratio, the porous wick geometry and thermal properties, the sink and ambient temperature levels, the design of the evaporator and compensation chamber, the elevation and tilt, the presence of non-condensable gases, the pressure drops of the fluid along the loop. The overall objective for this paper is to point the state-of-the-art for the related technology for future design and applications, where the constraints related to the LHPs are detailed and discussed.     

An Experimental Study on the Performance of a Stainless Steel-Water Loop Heat Pipe under Natural Cooling Condition简

Aiming to improve the thermal characteristics of modern electronics, we experimentally study the performance of a stainless steel/water loop heat pipe （LHP） under natural cooling condition. The LHP heat transfer performance, including start-up performance, temperature oscillation and total thermal resistance at different heat loads and with different incline angles have been investigated systematically. Experimental results show that at an optimal heat load （i.e. 60 W） and with the LHP being inclined 60~ to the horizontal plane, the total thermal resistance is lowered to be -0.24 K/W, and the temperature of evaporator could be controlled steadily at around 90~C.     

Flat Loop Heat Pipe with Bi-Transport Loops for Graphics Card Cooling

A flat loop heat pipe (FLHP) with bi-transport loops is developed for the cooling of graphics card with high heat flux up to 80W/cm². The evaporator and the pipes are made of copper and ultrapure water (electronic resistivity > 18 MΩ-cm) as the working fluid. To give the loop heat pipe (LHP) better performance, the evaporator is made in a flat shape to reduce the contact resistance between the evaporator and the chip. The advances of the LHP with bi-transport loops are discussed. The heat transfer performance is tested with different filling rate in different orientations. The test results show that the LHP can start up easily and can transport large amount of heat stably. The orientation of the condenser above the evaporator gives a better performance, and filling with 13 g of water gives a better performance. Limited by the evaporator temperature lower than 90°C, the LHP can transport 320 W when the evaporator is above the condenser and 380 W when the condenser is above the evaporator.     

Investigation of pulsations of the operating temperature in a miniature loop heat pipe

During the operation of miniature loop heat pipes (LHPs) one can observe pulsations of the operating temperature, which depend on the amount of the working fluid, the device orientation in the gravity field and the conditions of the condenser cooling. Intense pulsations, whose amplitude may exceed tens of degrees, arise from the lack of a working fluid in a LHP when a hot condensate or vapor bubbles periodically penetrate into the compensation chamber (CC) and act on the vapor phase in it, increasing its temperature and volume. Changes in the external conditions, for instance, the LHP arrangement in an unfavourable orientation or a more intensive cooling of the condenser with respect to the conditions for which the filling volume was optimal, also contribute to the initiation of intense pulsations of the operating temperature. In both cases one can observe redistribution of the working fluid between the condenser and the CC, as the result of which the liquid phase volume in the latter decreases and overshoots of vapor or a hot condensate there become possible.     

复合热沉环路热管的热点散热性能模拟研究

针对芯片功耗与集成度提高而导致的局部热点问题,设计了一种用于芯片散热的复合热沉环路热管系统。建立了环路热管蒸发段模型,通过数值模拟的方法,证明了复合热沉环路热管系统能够降低热点温度,提高散热表面的温度均匀程度,且散热效果与热点的分布位置有关。当热点的热流密度为160W/cm2,热沉横向、纵向导热率分别为1500W/(m?K)、24W/(m?K)时,热点温度为88.88°C,相比于无热沉时降低了5.96°C。研究了不同热沉导热率下的热沉厚度对热点温度的影响,结果表明：若导热率各项同性,热点温度随热沉厚度的增加而降低,之后趋向不变;若为各项异性,存在最优的热沉厚度,使热点温度最低。