Numerical investigation of impinging air jet heat transfer at low nozzle plate spacings

The local heat transfer characteristics of air jet impingement at low nozzle plate spacings have been examined CFD using PHOENICS package programme. Nusselt number was correlated for low nozzle plate spacings and Reynolds number. The effects of accelarating fluid between the nozzle plate gap as well as asignificant increase in local turbulence leads to substantially increased local heat transfer with decreased nozzle plate spacings. A stagnation point minimum surrounded by an iner and outer peak in the local heat transfer was observed for nozzle-plate spacings less than z/d=0,25. These primary and secondary maxima are explained by accelerated radial flow at the exit of the jet tube and an observed local maximum in the turbulence, respectively. These conclusions are drawn from observations made relative to the turbulent flow structure and wall pressure measurements. Key Words : Impinging air jet, PHOENICS, low nozzle-plate spacings, CFD