Management of surface cooling non-uniformity in spray cooling

Abstract

The existence of the hot spot area in the impact center of spray cooling indicates that the temperature is not uniform on a relative large spray-covered surface. In this study, the temperature distribution on a large spray-cooled surface is experimentally studied, and cooling non-uniformity (CNU) is defined to quantify the global and local temperature fluctuations. A flat thin film heater is newly designed, and surface temperature is measured using high-resolution infrared thermography. Particle Imaging Velocimetry (PIV) is used to acquire the droplet velocity of the spray. In the present work, three methods are investigated to reduce the CNU. One method is to change the height, the vertical spacing between the spray nozzle and surface. It is found that with the increasing spray height, the CNU first decreases to the lowest point and then rises to the peak value. The second method is to incline the spray. It is discovered that inclined spray impact benefits the cooling uniformity at the larger spray height. The third method is spray-jet cooling, in which a liquid jet is added to impinge at the center of the spray cooling. It shows that the spray-jet cooling does not only reduce CNU but also increases CHF.