Impingement Heat Transfer, Part II: Effect of Streamwise Pressure Gradient

Abstract

This is Part II of a two-part paper on jet-impingement heat transfer. The effect of streamwise pressure gradient on jet-impingement heat transfer is investigated. In realistic configurations, impingement arrays do not always impinge in channels that have parallel walls. Converging channels create positive pressure gradient, and diverging channels create adverse pressure gradient. In this study, the effect of nonparallel walls on jet-impingement heat transfer is investigated. Firstly for impingement arrays with jet-to-jet streamwise and spanwise spacing of fourhole diameters and eight-hole diameters and then for the linearly stretched arrays discussed in Part I. Two jet Reynolds numbers are studied for all cases for Re =6 × × 10 3 , and 10 3 . Also, the jet height-to-diameter ratio is increased from 1 to 5 to generate the adverse pressure gradient and decreased from 5 to 1 to generate the positive pressure gradient. Results show that the effect of streamwise pressure gradient alters the flow distribution causing significant variations in heat-transfer distributions. Accelerating flow causes streamwise jet stretching, whereas decelerating flow causes spanwise jet stretching. The results for converging and diverging channels are compared with results for parallel plate channels with different spacing to compare the effect of the streamwise pressure gradient.