Effect of dimple pitch and depth on jet impingement heat transfer over dimpled surface impinged by multiple jets

Abstract

The effect of dimpled surface configurations on heat transfer is investigated for multiple jets issuing from orifices arranged in a 3 × 3 array. The Reynolds numbers during these studies maintained in the range of 5000–40000. To assess the influence of jet and dimple pitch, the studies are performed for different dimple and orifice pitches (p = 3d, 4d, and 5d). Along with these cases, dimple depths of 0.25d and 0.5d and eccentricity between the orifice and the dimple are also studied. The distance between the orifice plate and the test surface is varied from 1d to 6d. To characterize the steady-state heat transfer from the heated target surface to the impinging air jet, the thermal image of the target surface captured with a thermal imaging camera is analysed with thin metal foil heater technique. To evaluate the effectiveness of jet impingement cooling of the dimpled surface, the average Nusselt number and coefficient of variance (COV) are calculated over a defined pitch area of ± p. It is observed that for the jet orifice and dimple pitches of three nozzle diameter (p = 3d), the flat plate is more efficient than a dimpled surface. However, for greater pitches (p ≥ 4d), the dimpled surface performed much better in comparison with the flat plate.In case of the shallow dimpled surface (t/d = 0.25), best heat transfer performance is observed for the pitch of 5d. The coefficient of variance (COV) suggests that the Nusselt number is more uniformly distributed for a pitch of 3d.