Effect of Strip-Fin Height On Jet Impingement Heat Transfer in a Rectangular Channel At Two Jet-to-target Surface Spacings

An experimental investigation of heat transfer performance in a rectangular impingement channel featuring staggered strip-fins was completed. Four configurations were considered to study the effects of varying the strip-fin height (H/d= 1.5 and 2.75) at two jet-to-target surface spacings (z/d= 3 and 6) on the heat transfer, pressure loss, and crossflow magnitude for a long impingement channel with in-line, 4×12 impinging jets. Also, the effect of the reference temperature choice, either jet inlet temperature or local bulk temperature, for calculating the local heat transfer coefficients was considered. The regionally averaged heat transfer coefficients were measured at seven Reynolds numbers, based on the jet diameter, (10k-70k) utilizing the copper plate experimental method. Supplemental CFD simulations for the flow field visualization were performed to explain the complex flow behavior of the impinging jets and the crossflow in the presence of strip-fin roughness elements. The results show that the trend of the local Nusselt number distribution varies along the streamwise direction due to the crossflow effect. The crossflow is independent of the Reynolds number. The discharge coefficients are similar for all configurations between Rejet = 10k and 50k. CFD velocity contours indicated high non-uniformity distributions near the target surface implying non-uniform heat transfer rates. Finally, empirical correlations were expressed for the area averaged Nusselt number estimation of impingement channels with pin-fin or strip-fin roughness elements.