Impingement Heat Transfer Within Arrays of Circular Jets: Part II—Effects of Crossflow in the Presence of Roughness Elements

Abstract

An experimental investigation was carried out to determine the effects of jet-induced crossflow on impingement heat transfer from rough surfaces. The jets impinged on surfaces having repeated square ribs, with transverse flow of the spent air. Two crossflow schemes were tested: discharge of the spent air through two opposite sides (intermediate crossflow) and through one side (complete or maximum crossflow) of the rectangular impingement surface. The rib height was fixed at 0.813 mm, while the pitch-to-height ratio (p /e) was varied between 6 and 10. The study covered standoff spacing and jet Reynolds number in the range 2 to 16 jet hole diameters and 1300 to 21,000, respectively. Three nozzle plates, having 48, 90, and 180 square-edged holes, were tested. For the maximum crossflow scheme, the presence of roughness results in small upstream reductions in heat transfer coefficient, with marked improvement in the downstream section; indicating that roughness elements can be used to compensate for the degradation that is usually associated with impingement on smooth surfaces.