Analysis and prediction of single-phase and two-phase cooling characteristics of intermittent sprays

Abstract

Intermittent spray cooling is an active flow control technique to enhance spray cooling performance, increase the efficiency of coolant usage, and reduce pumping power consumption. However, the cooling characteristics and mechanism of intermittent sprays have not been investigated sufficiently, especially in the nucleate boiling region and critical heat flux region. Methods that model intermittent spray cooling are insufficient and require expensive and laborious spray dynamic characteristics measurements for each operating condition. In this study, experiments were performed to investigate the effect of frequency and volumetric flux on the heat transfer characteristics of intermittent sprays at both the single- and two-phase regimes. The results demonstrate that both the volumetric flux and frequency affect the heat transfer. The commutative impact of two consecutive injection cycles would enhance the drop impact and spray-wall interference, corresponding to the results of the boiling curve and critical heat flux (CHF). However, this impact becomes more remarkable with increasing frequency and is suppressed gradually as the volumetric flux increases. Based on these results, the mechanism and model on heat transfer in an intermittent spray are proposed. The Strouhal number, representing the relative effects between the impact frequency and volumetric flux, is introduced to account for intermittent features, based upon which correlations of single phase, nucleate boiling, and CHF are developed.