两相冷却系统过热现象与启动温度关系分析

Analysis on Relationship Between Superheat Phenomena and Startup Temperature for Two-phase Cooling System

在以二氧化碳为工质的新型空间两相流冷却系统-机械泵驱动两相流冷却系统的实验过程中发现,在热量加载的同时在蒸发器出口将有过热现象产生。进一步的实验研究得出结论当启动过程蒸发温度越低,蒸发器出口的过热度也就越大,同时从过热状态变为两相状态所产生的压力脉冲也越大。通过经典核化理论的角度分析指出该现象的产生主要和工质的物性有关,又统计物理学和动力学成核理论方面分析指出随着蒸发温度的升高,核态沸腾产生气泡的直径变小,所以需要更少的热量就能推动从过热的亚稳态到更加稳定的两相状态的转变。

Experiments on the performance of a new mechanically pumped cooling loop （MPCL） using CO2 as a working fluid were conducted. It was observed during the experiment that there was a superheat phenomenon at the outlet of the evaporator when the heat load was added. Moreover, the superheat degree at the outlet of the evaporator and the pressure pulse caused by the change from superheat state to two-phase state increase with the decrease of the evaporating temperature at the start-up stage. The analysis based on nucleation thermodynamic theory indicated that the critical radius of bubbles would become smaller with the increasing of evaporative temperature. So, a relative lower heat power can change the work fluid from suoerheat into a stable two-phase state.