【作者】 刘志春；

【导师】 刘伟；

【作者基本信息】 华中科技大学 ， 工程热物理， 2006， 博士

【摘要】 毛细抽吸两相流体回路(CPL:Capillary Pumped Loop)是一种利用工质相变传递热量并且利用毛细力驱动系统循环的装置,具有高效、可靠、节能以及传输距离长等优点,在航天器热控以及电子装置冷却等方面具有广阔的应用前景。但是国内外的研究表明,由于各种原因传统CPL系统存在启动困难和运行过程中压力和温度的波动等问题,这严重制约了其应用发展。国内外许多学者就此问题展开了广泛而深入的研究,积极探索解决的方法。本文首先介绍了CPL系统的工作原理和运行特点,对国内外CPL系统的研究状况进行了述评,指出了传统CPL系统的缺点和不足。针对这些问题,并结合国内外研究经验,对传统的CPL系统进行了技术创新,设计并制造了一种新型平板式CPL系统。在所设计的新型平板式CPL系统中,蒸发器和冷凝器均采用带有毛细芯的平板式结构,系统中还设计了储液器用来控制和调节系统的温度;为了提高回流液的品质,系统中设计了过冷器。蒸发器的设计借鉴了LHP的蒸发器的设计,在回流液体入口侧设计了由纵横十字槽道构成的液体补偿腔,以提高系统的稳定性以及高热流密度工作特性;冷凝器采用新型的三通道平板式结构,而且在其中也采用了毛细芯结构,以改善系统的启动特性和稳定性;在系统的构成方面,与传统的CPL系统不同,储液器通过两条通道和系统回路进行流体交换,(1)储液器和冷凝器相连;(2)储液器和回流液体管道相连。这些创新设计可以大大改善系统的启动性能和调节性能。为了证明新型平板式CPL系统工作性能,针对所设计的新型平板式CPL系统建立了试验系统,对新型平板式CPL系统进行了启动和变工况等运行特性试验,实验证明,该系统在高、低热负荷下都具有可靠、简便的启动特性,稳定的变工况运行性能,并且在系统运行过程中没有出现系统干涸现象。众所周知,没有系统理论的指导,开发出的新技术、新产品将很难十全十美,也不可能足够完善,甚至使一些关键技术的突破受到制约和停滞不前,影响其进一步发展。因此本文围绕着所研制的新型平板式CPL系统,以系统和系统的关键部件蒸发器、冷凝器为研究对象,进行了一系列理论研究与分析。论文首次引入场协同原理分析新型平板式CPL系统的蒸发器毛细芯内的流动与传热特性,运用场协同原理分析工质在蒸发器毛细芯中的流动与传热情况,针对不同的蒸发器肋片结构参数、毛细多孔芯厚度以及不同的热流密度进行了数值分析,提出了CPL蒸发器结构以及性能优化的方向以及途径本文在对新型平板式CPL系统的启动过程分析的基础上,采用数值分析方法研究了新型平板式蒸发器的启动特征,并将数值计算结果和试验结果进行了比较,结果表明计算结果与实验结果较吻合。文中还研究了不同的平板式蒸发器结构系统启动性能对整个系统的影响,提出了改善CPL系统蒸发器的启动性能以及增强系统的稳定性的一些方法及措施。此外,论文还采用流体体积函数(VOF)模型分析了工质在毛细芯冷凝器中相变与流动传热情况,分析了不同的壁面温度以及不同的蒸汽入口速度对冷凝相变界面的影响。结果表明,采用毛细芯冷凝器结构可以抑制甚至消弱系统的压力波动。最后论文针对所研究的平板式CPL系统的具体情况,采用集总参数法建立了系统动态运行的数学模型,借助Matlab/Simulink进行仿真计算,并将仿真结果与实验结果进行了比较,结果表明该系统仿真模型在一定精度上可以反映平板式CPL系统的运行规律和特征。本文理论分析和实验研究结果的均表明,所研制的新型平板式CPL系统大大改善了系统启动性能,提高了系统运行的稳定性。更多还原

【Abstract】 The CPL (Capillary Pumped Loop) is such a system, of which the driven potential depends on the phase change of the working fluid and the capillary force, and therefore it has those characters that make it very suitable to the thermal management on the satellite and electronic component cooling, such as high reliability, energy saving and transferring heat over long distance, and so on.However, many investigations about CPL indicate that there are problems that plague the applications of CPL, such as startup difficulty and not being robust and reliable due to pressure oscillation during CPL operation. Therefore, how to restrain the hydrodynamic oscillation and improve evaporator startup become the crucial issue on CPL research and many researchers are now investigating these problems.This thesis first introduces the operation principles and characteristics of the CPL system, and gives some comments on CPL systems that have already been made and put into study. Based on this a new type of CPL system is constructed and tested in the present investigation, which combines the advantages of CPLs and LHPs (loop heat pipes) by improving configurations both for system and components. In the present CPL, both evaporator and condenser are designed as a type of flat plate with porous wick, and a reservoir is used to control and adjust operation temperature of the system. In addition, a sub-cooler is adopted to improve the quality of working fluid flowing back to evaporator. A plate type of evaporator with a cross channel for liquid supply was made to reduce the probability of dry-out point caused by strong evaporation in the case of high heat flux, and therefore to enhance the stability of the system. In addition, a plane type of condenser with porous wick is designed, which is of the three ports for vapor-pipe inlet, liquid-pipe outlet and adjusting pipe connected to reservoir. The startup performance of the system benefits greatly from this three-port design, as liquid in the system can be easily pressed into reservoir due to resistance reduction. In the present system configuration, the fluid exchange between the reservoir and the loop is through two ways: (1) from reservoir to condenser, and (2) from reservoir to liquid pipe line. This is very different from the traditional CPL, and can greatly improve the startup performance and the adjustment capability of the system. Startup experiments under different heat load and working conditions were conducted. Excellent startup performance, being stable and easy, has been shown for the plate type CPL system, which validates the new configuration. Pressure oscillation and temperature fluctuation in the system were reduced largely owing to the induction of porous wick in the plane condenser. During experimental processes lasting more than 10 hours, the new type CPL shows outstanding thermal behaviors and no dry-out phenomena were observed.In this thesis, the characteristics of flow and heat transfer under different geometrical structures and heat flux densities in the porous wick of a CPL evaporator have been numerically studied according to field synergy principle. The calculation results indicate that the heat flux density and geometrical structures, such as fin width and wick height, exert great impacts on the heat transfer of a CPL evaporator, which demonstrates that the field synergy principle can be applied to optimize the configuration of the evaporator and consequently to enhance the heat transfer in a CPL evaporator.During experimental research, a phenomena can be observed that the back conduction is significant in flat plate type of CPL evaporator and can not be ignored, which can impede the CPL operation. In order to improve the operation characteristics of flat plate type evaporator, the numerical simulation method is introduced to study startup characteristics. On the basis of these , some measures about improving startup and operation capabilities are presented.Based on VOF method, the change and flow in condenser with porous wick is studied, and numerical method is used to analysis the effects on condensation under different wall temperature and inlet velocity of vapor. The results present that a fixed condensation physical interface can be formed on the face of porous wick, which can restrain, even eliminate the pressure oscillation.The dynamic operational characteristic of this CPL is investigated based on the nodal method. Matlab/Simulink is employed to perform the simulation to obtain the operational parameters such as temperature and pressure during different heat loads. The simulated results are verified by experiment, showing a good accordance with the real ones and have good precision as well.The studied results both theoretically and experimentally demonstrate that flat plate type of CPL shows excellent performance in start-up, and has good stability during operation and adjustment process.更多还原