Monodisperse spray cooling of small surface areas at high heat flux

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.

Spray cooling is an effective method to remove high heat fluxes from electronic components. To understand the physical mechanisms, the current work studies heat transfer rates from single and dual nozzle sprays on a small heated surface (1.3 mm x 2 mm). Thermal lnk Jet (TIJ) atomizers generate small droplets, 33 um dia. at known frequencies leading to controlled spray conditions with a monodisperse stream of droplets interacting with the hot surface. Particular interest in this work is the dissipated heat flux and its relation to the liquid film thickness, the surface superheat, the cooling mass flow rate. Experimental results show the heat flux scales to the cooling mass flow rate. The limit of droplet spreading-splashing deposition has been reported to be K=57.7 (K=We1/2 *Re1/4 ) for an ambient temperature of 25 •c at the surface. Current experimental results at K=47.9 and K=27.2 for the surface temperatures of 140 "C and 120 "C indicating that a stable droplet spreading regime is achieved with little splashing. In addition, the liquid film thickness is investigated in relation to the heater superheat and a stable thin film is seen at superheats beyond 20 •c. The efficiency of the spray system is inversely related to the film thickness and may be due to ejection of liquid from the surface due to bursting of vapor bubbles.