Two-phase cooling characteristics of a multiple-intermittent spray

Abstract Among the new techniques capable of removing high heat fluxes, spray cooling appears to be a notable method with its ability of removing heat relying on phase-change (nucleate boiling), additionally to the convective heat transfer linked with fluid motion, but optimum performance requires a precise control of the liquid mass rate supplied for cooling and subsequent removal of the vapor produced. Previous works showed that a multiple-intermittent spray has the potential to achieve this by proper matching the duration of each injection with the frequency of successive injections, but the formulation of an accurate method to control the temperature of the surface demands for an exact knowledge of how the fluid dynamic characteristics of the spray correlates with the heat transfer phenomena. The work reported here addresses these issues based on simultaneous phase-Doppler anemometer measurements of the spray characteristics at impact and instantaneous surface temperature in a simplified flow geometry consisting of a pulsed spray issuing perpendicularly to a flat heated aluminum disc. Analysis of the results shows that the heat transfer behaves differently before and after closing of the injector. During the first period, the interaction occurs with a dense cluster of droplets, which is not altered by the rising thermal plume and heat transfer is governed by the number flux of droplets arriving at the surface; during the second period, interaction occurs with a sparse cluster of droplets and heat transfer is dominated by the kinetic energy of droplets at impact