Enhancement of Impinging Jet Heat Transfer Using Two Parallel Confining Plates Mounted near Rectangular Nozzle Exit

Impinging jet heat transfer on a target plate was enhanced by using two parallel confining plates mounted between a rectangular nozzle end plate and a jet target plate. The target plate was set equal to 2, 3, 4, and 5 times the jet exit width, , and the gap ratio of two parallel confining plates, , were changed from 2.7 to 8.0 only by impinging length and from 2.7 to 6.7 by . Two confining parallel plates mounted near the jet exit produced swing-type flow under some conditions. As a result, the maximum Nusselt number attained around the stagnation point was augmented by about 50% compared to the one for normal impinging jet without the two parallel plates and then spatial mean Nusselt number was increased by about 40%. 1. Introduction Impinging jets have been used in several industrial processes, for example, for cooling of steel, glass, electronic components, and gas turbine vanes, for drying of paper, film, and textiles, and for freezing food and tissue in cryosurgery, because the high heat and mass transfer coefficients can be obtained around a jet stagnation region and the heat transfer characteristics can be easily controlled. In the meantime, Deo et al. [1] have examined characteristics of turbulent jets issuing from rectangular nozzles with and without two parallel plates attached as sidewalls to the slot’s short sides. They reported that the potential core of the jet without sidewalls was shorter than that with sidewalls and the centerline turbulence intensity of the jet with sidewalls became asymptotical closer to the nozzle exit than that of the jet without sidewalls. The results suggest that a characteristic of impinging jet heat transfer on a target plate with sidewalls is different from that without sidewalls. By the way, jets often impinge onto a target body mounted in confined spaces for manufacturing processes of frozen food and heat treatment of electronic components, and so forth. San et al. [2] and Lin et al. [3] have studied heat transfer on a surface for mounting an end plate flush with a jet exit. Gao and Ewing [4] have examined static and fluctuating wall pressure and heat transfer on a surface for unconfined jets and confined jets with an end plate. They found that the location of the decrease in the heat transfer and the fluctuating wall pressure in the confined jets shifted laterally outward as a nozzle-to-plate distance increased. Fitzgerald and Garimella [5] have studied characteristics of the flow field of an axisymmetric, confined, and submerged turbulent jet impinging normally on a flat plate experimentally. They mapped