Experimental investigation on the small flow rate vacuum flash evaporation cooling for aerospace equipment

Flash evaporation cooling is a promising active thermal protection technique for aerospace equipment of high-speed aircraft working in low-pressure vacuum environments. However, the influencing factors of vacuum flash evaporation remain ambiguous especially under small mass flow rate conditions, which hinders the full utilization of coolant energy. Therefore, this work experimentally investigates the effects of key factors including initial superheat, mass flow rate and chamber pressure on flash evaporation cooling within 300 mm × 300 mm vacuum chamber. Experimental results indicate that the increasing initial superheat can lead to the change of cooling water from nucleate boiling to transition boiling, which prevents the bubble discharge from the surface and reduces the energy utilization efficiency. As the mass flow rate increases, the increment of cooling water's latent heat gradually exceeds that of radiation heat transfer, resulting in the maximum energy utilization efficiency of 92.9 % at 0.08 g/s. By comparison, the effect of chamber pressure is weak. As the chamber pressure decreases from 15 kPa to 5 kPa, the energy utilization efficiency increases only by 4.4 %. This study can provide the reference for designing the efficient vacuum flash evaporation cooling systems of high-speed aerospace equipment.