Heat transfer of impinging jet array with web-patterned grooves on nozzle plate

Abstract

Heat transfer performances of the impinging jet arrays issued from the nozzle plates without and with the two types of the interconnected grooves were experimentally studied at jet Reynolds numbers (Rej) and nozzle-to-plate distances (S) in the respective ranges of 1500–20,000 and 0.1–8 times of the nozzle diameters (dj). Owing to the significant spent flow confinement formulated between the smooth nozzle plate and the impinging surface at S/dj < 0.3, the mechanism of heat transfer enhancement (HTE) relevant to the impinging jet array was considerably suppressed. The relaxation of spent flow confinement by imprinting the web-patterned grooves on the nozzle plate at the small S/dj effectively resumed the HTE characteristic in association with the impinging jet array. At large S/dj, the additive ambient fluid entrainment from the grooves enriched the jet momentum to boost the heat transfer level from that produced by the smooth nozzle plate. Both the Nusselt number level and the heat transfer uniformity for the smooth and grooved nozzle plates were comparatively studied with the Rej and S/dj effects examined. In conformity with the experimental observations for the isolated and coupled Rej and S/dj effects, the regression-type analysis was performed to generate a set of empirical correlations that permitted the evaluation of the average Nusselt number (Nu) over the central jet region for each of the present impinging jet arrays.