A parametric study of liquid microjet impingement for electronics cooling

This paper presents the results of a numerical parametric analysis focusing on laminar microjet impingement cooling of electronics. A conjugate problem with the solid region representing an active IC chip and the fluid region encompassing the confined jet flow was solved with a commercial CFD software package based on the finite volume method. The flow parameters varied included the Reynolds number based on the microjet diameter, the dimensionless ratio of the nozzle-to-plate distance to the jet diameter (z/d) and the Prandtl number. The fluid flow pattern shows interesting features including a boundary layer separation point and a secondary recirculation zone downstream of the stagnation point that varies with the Reynolds number and z/d. Increasing z/d and Re are observed to push the secondary recirculation zone further downstream (radially) of the stagnation point. The strength of the secondary recirculation zone is enhanced with increasing Reynolds number and eventually reaches the top confining plate. The Nusselt number (Nu) shows a secondary peak akin to turbulent macrojet impingement (the primary peak is at the stagnation point) that coincides with the location of the reattachment of the main flow. Consequently, the secondary peak in the Nusselt number is shifted away from the stagnation point with an increase in the Reynolds number and a decrease in the z/d ratio. Increasing Prandtl numbers are shown to suppress the strength of the secondary peak. A parabolic inlet velocity profile is observed to increase the stagnation heat transfer coefficient and push the secondary recirculation zone toward the stagnation point. The fluid velocities at the exit of the impingement region however are very low because of the flow-channel geometry which motivates further research in this direction.