Spray cooling heat transfer enhancement by ethanol additive: Effect of Sauter mean diameter and fluid volumetric flux

Due to the excellent heat transfer performance, spray cooling is widely used for heat removal of high-heat-flux electronic devices. In this study, the influence of spray characteristics on spray cooling heat transfer is tested experimentally, where both water and 4% ethanol-water mixture are used as the working fluid. The Sauter mean diameter and droplet number distributions are measured by the Particle/Droplet Imaging Analysis system, and the fluid volumetric flux distributions are measured by the self-designed Precision Mobile Experiment Bench. The results show that the heat transfer efficiency of the 4% ethanol-water mixture is superior to that of water. Especially, the critical heat flux is about twofold that of water for the Spray A nozzle. For a fixed nozzle, the Sauter mean diameter of the 4% ethanol-water mixture is smaller, while the fluid volumetric flux shows an increase under the same conditions. Small Sauter mean diameter and large fluid volumetric flux can induce more droplets to entrain bubbles. Then the mechanisms of improved spray cooling heat transfer are analyzed based on the spray characteristics measurement results. It is revealed that the Sauter mean diameter and mean fluid volumetric flux exert joint influence on the heat transfer efficiency, and the mean fluid volumetric flux has an obvious effect between different nozzles. Two dimensionless heat flux correlations are proposed for the single-phase and nucleate boiling regimes with mean absolute errors of 15.56% and 14.68%, respectively. Highlights Sauter mean diameter of 4 vol.% ethanol-water is smaller than water, but the fluid volumetric flux is higher than water. Small Sauter mean diameter and large fluid volumetric flux induce more droplets generating entrained bubbles, which can enhance the heat transfer performance. Fluid volumetric flux is predominant in improving heat transfer performance, especially in the nucleate boiling regime. Spray characteristics have an obvious influence on the critical heat flux. Dimensionless heat flux is correlated with characteristic numbers integrating Sauter mean diameter and fluid volumetric flux.