| Two-phase mechanically pumped cooling loop (MPCL) is a promising thermal control system which is just like a loop heat pipe or capillary pumped loops to realize heat extraction from energetic electrical or electronic equipments efficiently. In this paper, a brief review of system design and work principle is presented and a proposed experimental system was described. The testing system was able to accomplish the thermal management of up to 1000 W by using CO2 as the working fluid. Then ,a serial tests were carried out ot investigate the MPCL systematically. It mainly includes the system startup, working set point controlling and running characteristic tests.The startup of a two-phase cooling system is a complex transient phenomenon, especially for the feasibility application of an MPCL. The experiments on the startup processes under variety of conditions were carried out. Special attention has been paid to the startups of the system in different evaporative temperature, various mass flow or heating load and some abnormal startup prehistory. The transient flow exchange between the main loop and accumulator was observed and discussed according to 3 different startup step which have been identified as pre-condition, pump startup and heat load startup. During the startup processes, the system presents a good stability and each part of the system performs a reasonable temperature wave, except some superheat phenomena in the evaporator. The superheat is mainly related to startup conditions such as evaporative temperature, mass flow, heat load or initial liquid distributions in a loop. In general, the lower the evaporative temperature is, the higher superheat occurs. A lower heat load or a larger mass flow may lead to a huge pressure impact and a long time superheat. In the following , experiments have been carried out on how to cool the accumulator and realize a stable set point temperature. The paper points out a novel method to combine thermoelectric coolers (TEC) with the branch of a main loop. The novel method is realized by the use of the cold plate of TEC to control the set point while the hot plate is cooled down by the subcooled liquid in branch loop. Tests result have proved the feasibility and stability of the new design which not only uprates the accuracy from±0.4℃to±0.1℃and increases the cooling speed to 0.36℃/min under 10W TEC input power ,but also finds a novel way to improve the efficiency of a TEC by using subcooled fluid to dissipate heat from the hot plate.During the running characteristic tests, the stable and transient experiments have been investigated. Tests mainly included sinusoidal temperature variations of boundary condition, heat load or mass flow fluctuation , unbalanced heat load on the evaporators and so on. According to the experimental findings, The transient liquid distribution between the main loop and accumulator was analyzed to find the factors for system stability. From the experiments, it is found that the system presents a good pressure performance of the loop and is able to handle large temperature wave and heat impacts perfectly.In conclusion, important performance characteristics demonstrated by this paper included: 1) Operation of an active two-phase thermal system driven by mechanical pump with dual-evaporator; 2) sussessful startup processes in different situations; 3) Effectiveness of TECs and a rapid dropping speed in controlling the MPCL operating temperature and a higher controlling accuracy of the evaporators; 4)Robustness and reliability running of the system under various test conditions if temperature at the pump's inlet has enough sub-cooling to keep a liquid state and vapor quality is less than 0.5 at the evaporator outlet. |
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