Heat transfer characteristics of spray cooling beyond critical heat flux under severe heat dissipation condition

Spray cooling is considered to be an effective cooling method for metal processing, medical treatment, and laser weapon cooling applications. An experimental prototype closed-loop spray cooling system was fabricated to investigate the heat transfer characteristics beyond the critical heat flux (CHF). The results indicated that the heat transfer performance significantly deteriorated when the CHF was achieved. At that moment, the surface temperature increased, and the heat transfer coefficient decreased to 0.17–0.2 W/(cm²·K). When the heat flux decreased, the boiling heat transfer ability recovered, and the heat transfer coefficient increased. It can be inferred that a vapor film formed on the heating surface, which isolated it from the droplets when the critical heat flux was achieved. Four dimensionless parameters representing the impact of the droplets, flow of the liquid film, evaporating heat transfer, and boiling heat transfer were selected to analyze the spray cooling mechanism. When the CHF was achieved, these four parameters accelerated the decrease in the heat transfer coefficient. During the cooling process, the decrease in Ja and increase in ε were the key factors in the recovery of the heat transfer ability. New correlations for spray cooling were developed based on the experimental results.