Startup regimes of minichannel evaporator in a mechanically pumped fluid loop

摘要

The startup process of minichannel evaporator in a two-phase mechanically pumped fluid loop is investigated by a visualized experimental system, with a particular focus on the dynamic temperature response under step heat load. The effects of heat load, flow rate and supercooling degree on the startup behaviors of the minichannel evaporator are examined and analyzed. A startup regime diagram is provided to quantitatively recognize the startup behavior, depending on Jacob number and Weber number. The results indicate that the gradual startup, once-rise overshoot startup and twice-rise overshoot startup are observed and sequentially experienced for a minichannel evaporator as the step heat load increases. The temperature overshoot is essentially induced by the boiling incipience. The dominated heat transfer mechanism is always the single-phase convection during the gradual startup process, and it changes from the single-phase convection to nucleate boiling during the once-rise overshoot startup process. In addition, it shifts from the single-phase convection to nucleate boiling, and then is the convective evaporation during the twice-rise overshoot startup process. The increase in Weber number leads to a larger critical Jacob number of the startup regime transition, and hence the range of Jacob number tends to be larger for the once-rise overshoot startup mode. Particularly, a higher supercooling degree also induces a larger range of Jacob number for the once-rise overshoot startup mode.