Enhanced Spray Cooling Using Micropillar Arrays: A Systematic Study

The role of contact-line evaporation on spray impingement heat transfer is systematically studied by spraying de-ionized water on silicon substrates with micropillar arrays. The height, the pillar diameter, and the spacing of the micropillar array were varied from 5 to 50 mu m while keeping the porosity constant at 0.75. An air-assisted nozzle was used to create a liquid spray with a Sauter mean diameter (SMD) of similar to 22 to 42 mu m depending on flow conditions. Most test runs were conducted at a water flow rate of 30 ml/min and an air-liquid mass flow rate ratio of similar to 0.57. The results show a continuous increase in the critical heat flux (CHF) as the pillar diameter is decreased. The effects of pillar height are nonmonotonic, with CHF and peak heat transfer coefficient attaining a maximum as the height-to-diameter ratio approaches unity. Values of CHF as high as 830 W/cm(2)were achieved, along with cooling efficiencies of 49%. The effect of liquid flow rates and air-flow rates were also investigated independently using textured surfaces.