Influence of the nozzle shape on heat transfer uniformity for in-line array of impinging air jets

•Effect of nozzle shape on heat transfer uniformity is investigated experimentally.•Two different shapes, circular and square, arranged in-line array are considered.•Heat transfer rate is higher for the circular nozzle than for square nozzle.•Uniformity of heat transfer is higher for square nozzle than circular nozzle.•Uniformity of heat transfer is effected more by S/Dh than by H/Dh for both nozzles. The objective of the present work is to study the influence of nozzle shape on the uniformity of heat transfer for normal jets impinging on smooth flat surface. In the current study, in-line array of nozzles with different shapes, viz circular and square, with equivalent hydraulic diameter of 7.5mm are used. The uniformity of heat transfer (U) is investigated at Reynolds numbers (Re) ranged from 2000 to 10,000 and the spacing distance (S/Dh) and the separation distance (H/Dh) are each varied from 2 to 8. The experimental results of the average heat transfer are found to be 7.8% higher for circular nozzles than that for square nozzles. The maximum values of local and average Nusselt numbers are obtained at spacing distance of 4 for circular nozzles. On the other hand, the uniformity of heat transfer is improved approximately by 10.7% for a square nozzles as compared to a circular nozzles. Furthermore, the experiments indicate that the uniformity of heat transfer is influenced significantly by the jet-to-jet distance than the jet to plate distance. This implementation presents empirical correlations to compute the average Nusselt numbers as well as the uniformity of heat transfer for both circular and square nozzles.