HEAT TRANSFER IN CONFINED LAMINAR AXISYMMETRIC IMPINGING JETS AT SMALL NOZZLE-PLATE DISTANCES: THE ROLE OF UPSTREAM VORTICITY DIFFUSION

Abstract

In laminar impinging flow heat transfer it is well known that at small nozzle-to-plate distances the Nusselt number distribution displays an off-stagnation point maxima located one nozzle radius away from the stagnation point. This article demonstrates that the occurrence of the off-stagnation point maxima is entirely a consequence of upstream flow development because of vorticity diffusion. It is not because of local acceleration of the mean radial flow as suggested in the existing literature. Numerical results are presented to analyze the variation in the peak-to-stagnation Nusselt number ratio as a function of the dimensionless nozzle-to-plate distance and the Reynolds and Prandtl numbers. The calculations correctly predict the disappearance of the off-stagnation point maxima at dimensionless nozzle-to-plate distances larger than 3/8.