Heat transfer in confined laminar axisymmetric impinging jets at small nozzle-plate distances: The role of upstream vorticity diffusion

In laminar impinging flow heat transfer it is well known that at small nozz le-to-plate distances the Nusselt number distribution displays an off-stagn ation point maxima located one nozzle radius away from the stagnation point . This article demonstrates that the occur ence of the off-stagnation point maxima is entirely a consequence of upstream flow development because of v orticity diffusion. It is not because of local acceleration of the mean rad ial flow as suggested in the existing literature. Numerical results are pre sented to radial flow as suggested in the existing literature. Numerical re sults are presented to analyze the variation in the peak-to-stagnation Nuss elt number ratio as a function of the dimensionless nozzle-to-plate distanc e and the Reynolds ann Prandtl numbers. Thc calculations correctly predict the disappearance of the off-stagnation point maxima at dimensionless nozzl e-to-plate distances larger than (3/)(8).