Experimental investigation on startup of a novel two-phase cooling loop

The startup of a two-phase cooling system is a complex transient phenomenon, especially for the mechanically pumped two-phase cooling loop (MPCL), which is a promising thermal control method for extracting heat from large electronic equipments efficiently. In this paper, the system design and work principle as well as the test setup of an MPCL are presented and the startup processes of the MPCL are studied. 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 different startup sections, 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 evaporative temperature and the initial liquid distribution in the evaporator. In general, the lower the evaporative temperature is, the higher superheat occurs. In conclusion, the startup processes in different situations may cause some liquid superheats and evaporator temperature overshoots, but they will not affect much on the steady state operation of the MPCL.