Spray cooling at low system pressure

Spray cooling has been shown to be the best cooling technique for applications that require efficient high heat flux removal. This research presents a study of spray cooling at low system pressure that allows control of the surface temperature by controlling the boiling point of the fluid. Such cooling provides an attractive, low-temperature thermal control to industries such as electronics, avionics, lasers, and electro-optics. Experiments were conducted with a 1 cm/sup 2/-heated surface cooled by a spray nozzle at reduced system pressures. System pressures range from 0.015 to 1 bar. The heat transfer coefficient was determined by measuring the surface temperatures at increasing heat fluxes. The present study has shown that spray cooling with water at reduced system pressure can significantly decrease the surface temperature as compared to ambient pressure spray cooling. This study shows that at a pressure of 0.015 bar, the surface temperature can be cooled to 54/spl deg/C with 11/spl deg/C liquid at a heat flux of 380 W/cm/sup 2/, while the surface temperature at 380 W/cm/sup 2/ is about 120/spl deg/C with same liquid temperature at ambient pressure. The heat transfer coefficients measured here were on the order of 100,000 W/m/sup 2//spl middot/K. This study is limited by the heating source, which cannot exceed 400 W/cm/sup 2/. The maximum heat flux that can be removed by spray cooling at low pressure has yet to be determined.