Jet Impingement Cooling of Chips Equipped With Multiple Cylindrical Pedestal Fins

Fluid flow and heat transfer characteristics on and around a central pedestal and a secondary pedestal, mounted on a flat surface with an impinging jet, are investigated. Surface Nusselt numbers, pressure coefficients (in the form of normalized wall static pressure relative to freestream static pressure), and flow visualization results are given for jet Reynolds numbers of 23,000 and 2300. The dimensionless nozzle-to-surface distance $L∕d$ is 2, and the nondimensional height of the central pedestal $H∕D$ is 0.5. Results are given for different secondary pedestal heights and locations. Spatially averaged Nusselt numbers measured with secondary pedestals employed are 13% to 33% higher than values measured with no secondary pedestal. Local Nusselt numbers and wall pressure coefficients, measured with the secondary pedestal present, are different from values measured with no secondary pedestal, because of flow reattachment and the two counter-rotating recirculation zones located between the two pedestals, and small local regions of flow separation and recirculation located on top of the secondary pedestal. As such, the present multiple pedestal data with impinging jets are useful for a variety of electronics cooling arrangements.