【作者】 万忠民；

【导师】 刘伟；

【作者基本信息】 华中科技大学 ， 工程热物理， 2007， 博士

【摘要】 热毛细泵相变回路包括毛细泵抽吸两相环路(CPL)以及环路热管(LHP),由于采用工质相变传输热量以及利用毛细力提供循环的动力,因此具有传热能力强,热阻低、等温性好、效率高、无运动部件以及传输距离长等优点,从而使其成为了航天器热控以及电子器件高热流密度散热的有效方式。本文对CPL/LHP系统的研究现状进行了综述,介绍了CPL/LHP系统的工作原理及其运行特点,论述了CPL/LHP在实现高热流散热方面的优势,同时由于平板型CPL/LHP系统的平面型结构能更好的与器件表面贴合,相对于圆柱型蒸发器,减少了蒸发器与发热器件表面的传热热阻,提高了系统的传热效率,同时使散热表面的等温性更好。本文的工作正是对小型平板CPL/LHP系统进行研究。分析了小型平板CPL不同工质时系统的压力损失与毛细芯的毛细抽吸力,得出采用氨工质有着较好的传热性能和更高的毛细极限,同时得出影响系统毛细限的主要因素是蒸汽联管管径和工质的蒸汽密度,从而提出了工质传输系数作为CPL/LHP系统选取工质的重要指标。快速、简单、可靠的启动性能是一个先进的CPL/LHP系统所具备的基本特性,但是国内外的研究表明,由于各种原因使CPL/LHP系统在启动过程中出现了启动困难的问题,而各国学者对其的研究却非常的稀少,特别是特殊的平板结构使其具启动过程呈现出新的特点。本文分析了小型平板蒸发器预热启动过程的特点,并且对引起蒸发器启动失败的可能原因进行了理论分析,建立了小型平板蒸发器满液启动过程的非稳态数学模型,并用SIMPLE程序对模型进行求解,得出了蒸发器不同启动热流、不同的金属外壁材料以及不同的毛细多孔芯对蒸发器启动特性的影响。对毛细蒸发器的研究,以往都是针对蒸发器多孔芯的一个很小局部单元结构进行数学建模,没有考虑蒸发器金属外壁以及蒸汽、液体槽道的影响,这显然不能真实的反映蒸发器工作过程,更不能对系统的传热性能进行有效的评价,同时散热表面温度水平也不能得出。本文首次在考虑了金属壁的边界效应的情况下,建立了蒸发器毛细多孔芯、金属壁面、蒸汽槽道以及液体槽道内传热传质的整场数学模型。并运用SIMPLE程序设计了一种新的算法对小型平板蒸发器进行了整场耦合求解。研究了不同的加热热流、入口液体过冷度、金属材料对蒸发器性能的影响,结果表明小型平板蒸发器存在着侧壁效应传热极限,它是影响系统最大传热量的一个重要极限;采用组合结构蒸发器以及蒸发器下壁增设翅片都可以提高系统的传热能力。针对微小型散热系统的需求,设计出新的微小型CPL/LHP平板式蒸发器,用液体补偿腔代替原来的一字形液体补偿槽道,采用更小有效孔隙半径的烧结金属芯,采用性能较好的高纯氨,来提高CPL/LHP系统的传热能力。建立了微小型蒸发器毛细芯流动与传热与相变模型,液体补偿腔的流动与传热模型,同时对蒸汽槽道、金属壁面建立了导热模型,运用SIMPLE程序对蒸发器进行了整体耦合数值求解。研究了不同的热流、多孔芯材料和外壁材料以及非均匀热流对蒸发器传热性能的影响,得出的结果为微小型平板蒸发器的设计提供了理论指导。分析了小型平板LHP系统的运行特性以及各部件之间流动与传热的相互关系,采用集总参数法建立了平板蒸发器、冷凝器、蒸汽联管以及液体联管的数学模型模块,运用MATALAB/Simulink对整个系统的动态平衡方程进行了仿真研究,得出了小型平板LHP的动态运行特性,为后续的试验起到了理论指导意义。更多还原

【Abstract】 The capillary pumped loop (CPL) and the loop heat pipe (LHP) are the two-phase thermal control devices with the latent heat of evaporation of a working fluid to transfer heat and the capillary action for fluid transport, which are capable of transport large heat density and passively transporting heat over large distances with minimal temperature losses, and contain no moving parts. As a result, CPL/LHP becomes more active and interesting in many engineering domains including thermal management of satellites and spacecrafts as well as cooling of electronic devices.The research progress in the CPL/LHP technology is briefly reviewed, and the operational principles and characteristics of CPL/LHP systems are introduced in this paper. CPL/LHP is especially well suited for thermal management of dissipating high heat flux, at the same time, due to the flat plate evaporator has the advantages of perfect thermal contact between evaporator surface and electronics devices surface, and low thermal resistance and isothermal heated surface, our primary interest in this investigation is small scale flat plate CPL/LHP.The total pressure loss along small scale flat plate CPL loop and maximum capillary pressure of the evaporator wick for different working fluids are obtained The analysis results showed that ammonia working fluid had better performance and higher capillary limit, and capillary limit is affected significantly by vapor line radius and working fluid density. The working fluid transmission coefficient is introduced as an important criterion of choosing working fluid in the CPL/LHP system.The speediness, simpleness and robustness should be the startup characteristics of advanced CPL/LHP system, but many investigations indicate that there are some problems which plague the applications of CPL/LHP, such as startup difficulty and not being robust. Few researchers focus on the startup process of CPL/LHP, especially on the startup process of small scale flat plate evaporator, which appears the new characteristics during startup process. The features of startup process and the reasons which result in the failure of small-scale flat-plate type capillary pumped loop(CPL)evaporator during the preheating stage are analyzed in the present work. The unsteady heat transfer model of evaporator in the fully-flooded startup stage is presented, and the model is solved by SIMPLE algorithm. The influences of heat flux, wick material and metallic wall material on the evaporator performance are discussed in detail.In the previous works on the capillary evaporator, the computational domain adopted is a single segment of wick structure in the evaporator, which is only a very small part of wick, and it leads to some shortages in evaluating the overall evaporator performance by those models. Firstly, these models can not predict the influences of metallic wall, vapor grooves and compensation cavity on heat and mass transfer of the capillary evaporator, the heated surface temperature which is very important in estimating the performance of thermal management system can not obtained, too. Two-dimensional mathematical model of the small-scale flat plate CPL/LHP evaporator is presented to simulate heat and mass transfer in the capillary porous structure and heat transfer in the vapor grooves and metallic wall for the first time. The overall evaporator is solved with SIMPLE algorithm as a conjugate problem. The influences of heat flux, liquid subcooling and metallic wall material on the evaporator performance are discussed in detail. The numerical results show that there exists a side wall effect heat transfer limit for small scale flat plate CPL/LHP evaporator, and the evaporator with combined wall or fins in the bottom can improve the heat transfer capacity remarkably. The conjugate model offers a numerical investigation in the explanation of the robustness of the flat plate CPL/LHP operation.Due to dissipating high heat flux requirements of small system, new miniature flat plate CPL/LHP evaporator have been designed, which utilizes the compensation cavity replacing the liquid grooves, uses the metallic sintered wick with smaller effective capillary radius and utilizes the high pure ammonia to improve the heat transfer capacity of CPL/LHP. The overall numerical model for the global evaporator of miniature flat plate CPL/LHP is developed to describe the heat and mass transfer with phase change in the porous wick , liquid flow and heat transfer in the compensation cavity and heat transfer in the vapor grooves and metallic wall. The governing equations for different zones are solved as a conjugate problem. The influences of uniform heat flux, liquid subcooling, wick material, metallic wall material and non-uniform heat flux on the evaporator performance are studied in detail. The results are useful for the evaporator design and performance optimization of miniature flat plate CPL/LHP.The dynamic operational characteristics of small scale flat plate LHP has been analyzed, and the mathematical models of flat plate evaporator, condenser, vapor liquid transport line and liquid transport line are developed based on the nodal method. MATALAB/Simulink is used to perform the simulation to obtain the operational parameters. The dynamic parameters are useful for the design of subsequent experiment of CPL/LHP.更多还原