Effect of nozzle geometry of turbulent jet on the impingement heat transfer to a flat plate

An experimental investigation of the impinging jet cooling from a heated flat plate has been carried out using nozzle and orifice for four Reynolds numbers of 20000, 35000, 45000 and 55000 and nozzle to plate distances (H/D) of 4, 6, 8 and 10. The results indicate that the maximum heat transfer occurs from the heated plate at stagnation point and decreases with radial distances for all cases. Interestingly, the maximum values of the stagnation as well as average Nu for Re=55000 is found to occur at separation distance, H/D = 6.0 for orifice and at 8.0 for nozzle respectively. Hence the nozzle can be preferred over orifice particularly for higher separation distance situation from heat transfer point of view. The minimum stagnation Nusselt number is obtained at H/D=10 for both orifice and nozzle. The enhancement of heat transfer as high as 14.2 % can be obtained using nozzle. However, the nozzle reduces the heat transfer for all other separation distances.