Jet Impingement Cooling of Chips Equipped With Cylindrical Pedestal Profile Fins

Surface Nusselt numbers, pressure coefficients, and flow visualizations are presented which are measured as a turbulent jet, with a fully developed velocity profile, impinges on the cylindrical pedestal and on the surrounding flat surface. Thermochromic liquid crystals and shroud-transient techniques are used to measure spatially resolved surface temperature distributions, which are used to deduce local Nusselt numbers. Dimensionless pedestal heights $H/D$ are 0, 0.5, 1.0, and 1.5, the jet Reynolds number Re is 23,000, and the surface distance to nozzle diameter $L/d$ ranges from 2 to 10. Local Nusselt numbers drastically increase with a radial distance away from the stagnation point on top of the pedestal for $H/D$ values of 0.5, 1.0, and 1.5. These are partially due to the small flow recirculation zones present on top of the pedestal, and mixing associated with the separation of flow streamlines near the edge of the upper surface on the pedestal. Local Nusselt numbers are also augmented at flat surface locations corresponding to positions where shear layers reattach downstream of the pedestal. In general, augmentation magnitudes become more pronounced as $H/D$ becomes smaller because of greater vortex influences. Corresponding local Nusselt numbers, beneath shear layer reattachment locations for H/D=0.5, are 35 to 80% higher than values measured at the same flat surface locations when no pedestals are employed.