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 μm 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 ~22 to 42 μm 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 ~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/cm2 were achieved, along with cooling efficiencies of 49%. The effect of liquid flow rates and airflow rates were also investigated independently using textured surfaces.
Bibliographical noteFunding Information:
Portions of this work were conducted in the Minnesota Nano-Center, which is supported by the National Science Foundation through the National Nano-Coordinated Infrastructure Network (NNCI) under Award Number ECCS-1542202.