Influence of Superhydrophobic Surface Microstructure on Transient Jet Impingement Cooling

Abstract Water jet impingement is an effective method of rapidly cooling a surface, but heat transfer from the surface is highly dependent on the surface condition and properties. Here, the impact of a superhydrophobic (SH) surface on heat transfer to an impinging, axisymmetric, room-temperature water jet with Re = 6×103 to 18×103 is explored. SH surfaces are created by etching thin silicon wafers to form different micropatterns (posts or holes). Surfaces are heated to between 200 and 320 °C, and the local surface temperature is measured with a thermal camera. The time resolved heat transfer from the surface and speed at which the thin film front spreads are measured. Local surface heat flux from the surface to the jet is calculated using an instantaneous energy balance. Heat transfer is shown to be highly dependent on jet Re and initial surface temperature. Results also show that varying microstructure by feature shape, width or diameter, and pitch (distance between features) individually did not reveal a systematic effect. However, when a surface roughness parameter is computed, the data followed a systematic variation. An increase in roughness resulted in a corresponding increase in time for the thin film to advance and a decrease in heat transfer rate. Interestingly, microstructure height alone did yield an impact, where a decrease in post height from 25 to 5 μm led to an increase in local heat flux of up to 90% for low Re cases.