Simulation of compressible micro-scale jet impingement heat transfer

A computational study is presented of the heat transfer performance of a micro-scale, axisymmetric, confined jet impinging on a flat surface with an embedded uniform heat flux disk. The jet flow occurs at large, subsonic Mach numbers (0.2 to 0.8) and low Reynolds numbers (419 to 1782) at two impingement distances. The flow is characterized by a Knudsen number of 0.01, based on the viscous boundary layer thickness, which is large enough to warrant consideration of slip-flow boundary conditions along the impingement surface. The effects of Mach number, compressibility, and slip-flow on heat transfer are presented. The local Nusselt number distributions are shown along with the velocity, pressure, density and temperature fields near the impingement surface. Results show that the wall temperature decreases with increasing Mach number, M, exhibiting a minimum local value at r/R = 1.6 for the highest M. The slip velocity also increases with M, showing peak values near r/R = 1.4 for all M. The resulting Nusselt number increases with increasing M, and local maxima are observed near r/R = 1.20, rather than at the centerline. In general, compressibility improves heat transfer due to increased fluid density near the impinging surface. The inclusion of slip-velocity and the accompanying wall temperature jump increases the predicted rate of heat transfer by as much as 8-10% for M between 0.4 and 0.8.