Theoretical Analysis And Experimental Study On A New Type Of Flat Plate CPL

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.