Heat transfer characteristics of swirling impinging jet-arrays issued from nozzle plates with and without webbed grooves

Heat transfer characteristics of the swirling impinging jet-arrays issued from the nozzle plates without and with the # and ※patterned grooves were comparatively studied. Each swirling jet was induced by the twisted tape with 1 or 2 twist pitches in the nozzle. The detailed Nusselt number distributions over the impingement surface for the six types of swirling jet-arrays were measured using the infrared thermography method at jet Reynolds numbers and nozzle-to-plate distances between 1500-20000 and 0.1–8 nozzle diameters respectively. A selective set of experimental results illustrated the effects of jet Reynolds number, nozzle-to-plate distance and the grooves on the local and regionally averaged heat transfer performances with the heat transfer uniformity over the impingement surface examined. In conformity with the effects of jet Reynolds number and nozzle-to-plate distance disclosed by the present study, a set of heat transfer correlations that evaluated the average Nusselt numbers over the central jet region of the swirling impinging jet-arrays issued from the nozzle plates without and with the grooves were generated.