EFFECT OF JET-JET SPACING ON CONVECTIVE HEAT-TRANSFER TO CONFINED, IMPINGING ARRAYS OF AXISYMMETRICAL AIR-JETS

The effects of jet-jet spacing (X(n)/D), low nozzle-plate spacings (H/ D = 0.25, 1.0 and 6.0) and spent air exits located between the jet ori fices were studied on the magnitude and uniformity of the convective h eat transfer coefficients for confined 3 x 3 square arrays of isotherm al axisymmetric air jets impinging normally to a heated surface. Local and average Nusselt numbers are presented for Reynolds number range o f 3500-20 400. The local Nusselt numbers illustrate the (non) uniformi ty of the heat transfer and aid in understanding the variations in the average Nusselt number. The jet-jet spacing affects the convective co efficient by varying the influence of the adjacent jet interference an d fraction of the impingement surface covered by the wall jet. The add ition of spent air exits increased the convective coefficient and infl uenced the location of the optimum separation distance. In addition, s ignificant enhancement of the uniformity and the convective coefficien ts was observed at H/D = 0.25 and 1.0 when compared to H/D = 6.0.