High Heat Flux Spray Cooling and Efficiency Correlation Obtained Using Precise Mono-Disperse Sprays

The effective dissipation of high heat fluxes at low superheats has become increasingly important in different industries to dissipate high heat fluxes and control hot spots. Heat flux dissipations in the order of 10 kW/cm² are being demanded. Two phase techniques have the potential to remove high heat transfer rates at relatively low superheating. However, their complex implementation due to the large heat transfer and fluid dynamic phenomena occurring during the evaporation makes it necessary to improve our understanding of the heat transfer at the micro scale to obtain high heat fluxes in an efficient way.;This work is aimed at cooling small surfaces (1-15 mm² in area) using distilled water spray droplets from Thermal Ink Jet (TIJ) atomizers. Custom built circuitry provides precise control to activate thermal atomizers to generate mono-disperse droplets (∼33 mum diameter) at known frequencies. The droplets impact the hot substrate forming a liquid film that evaporates according to the substrate superheating. Particular interest in this work include: obtaining high heat fluxes near the CHF; understanding the correlation between the heat dissipation efficiency (eta) and the liquid film thickness (delta) providing experimental data; and understanding the primary mode of heat transfer on spray cooling at different liquid film thickness. Experimental results indicate that high heat fluxes (∼4x107 W/m²) are achievable for controlled conditions of cooling mass flow rate, and the correlation between the efficiency and the liquid film thickness indicate higher efficiencies are achieved at smaller liquid film thickness (delta≈5mm → eta≈0.9). The heat transfer by conduction becomes dominant as delta decreases.