A study of spray-impingement cooling on smooth and pin-finned surfaces using fc-72

This manuscript presents the experimental results of the cooling performance of a pin-finned surface and a smooth surface in a spray-cooling device. Five orifices of either 0.23 or 0.56 mm diameter were made on the spraying device. dielectric fluid, FC-72, was used as the working fluid and the test section was maintained at 50°C saturation temperature. The total flow rate varied between 24.5 and 99.1 ml/min, and the heat flux varied from 60 to 800 kW/m². The results showed that the larger orifices (0.56 mm) provided a thicker liquid layer on the surface, and resulted in a greater critical heat flux and higher performance at high heat fluxes than the smaller orifices (0.23 mm). The smaller orifices (0.23 mm diameter) of the liquid distributor created stronger impingement on the test surface, and yielded better heat transfer performance at low heat fluxes. Spray-impingement cooling yielded up to 50% greater heat transfer coefficients than pool boiling at low heat fluxes for both surfaces. The pin-finned surface yielded ̃10%-40% enhancement as compared with the smooth surface for heat flux > 200 kW/m ². A correlation of spray-impingement cooling heat transfer coefficient of the fully wetted smooth surface is proposed. The prediction of this correlation agrees with the experimental data within ±25%.