Effects of nozzle positioning on single-phase spray cooling

The effects of nozzle positioning on spray cooling is experimentally studied using water sprays generated by a full-cone nozzle to cool a sputter-coated thin-film heater on a silicon wafer. Infrared camera is used to measure surface temperature with high spatial resolution. The nozzle positioning can be adjusted by moving the nozzle toward or away from the cooling surface to change spray height and/or by tilting the nozzle to change inclination angle. The study is composed of three components: (1). Flow in the spray cone is specified by polar and azimuthal angles (beta, phi), and it impacts and cools the surface at (x,y). The relation between the two coordinates, and the flow flux as a function of (beta, phi) are derived, and both are dependent on the spray height and inclination angle. (2). The effect of spray height is experimentally investigated for normal spray impact. It is discovered that the optimal spray height providing the most effective cooling is smaller than the height required for covering the entire heater area. It is found that the optimal height decreases with increasing the spray flow rate. (3). The effect of inclination is experimentally studied by changing the inclination angle while maintaining the major-axis length of the elliptical spray-covered area constant. Using the derived relation, from the measured local cooling at (x,y) we track the cooling performance of the flow at (beta, phi). The flux of the flow is calculated and compared using the derived flux equation for varied inclination angles. The enhancement and diminishment of the cooling performance are found to be in general agreement with the increase and decrease of the flow flux. (C) 2017 Elsevier Ltd. All rights reserved.