Experimental Investigation of Electrospray Cooling Performance Using the Mixture of Ethanol and R141b

The electrospray (ES) cooling technique, which is a combination of spray cooling and high-voltage electrostatic technology, has attracted considerable interest because of its simple unit structure and low power consumption. To overcome the low flow rate and high boiling point problems of current working fluids, a mixture of R141b and ethanol was used as the working fluid to experimentally investigate the break-up modes at a high flow rate. Furthermore, the effects of break-up modes and ethanol concentration on spray characteristics, cooling performance, and impingement characteristics were examined. The experimental results indicated that ES at a high flow rate exhibited four break-up modes: dropwise, varicose, whipping, and ramified. As the spray mode transitioned from the dropwise to the ramified mode, the droplet size decreased, and the droplet splash phenomenon on the hot surface was suppressed. The cooling performance was considerably enhanced with the evolution of the break-up mode, and the critical heat flux (CHF) was increased by 27.3 % when the break-up mode was transformed into the ramified mode from the dropwise mode. Under certain conditions, an ES cooling efficiency of 92.6 % was achieved. Furthermore, the volume fraction of ethanol (corresponding to the best cooling performance) increased with the wall temperature. In this study, considering the actual requirements of the chip for the cooling capacity, the optimal volume fraction of ethanol in the whole temperature region was determined to be 30 %. These findings can provide theoretical guidance for thermal management of high-power electronic devices.