Pulsating circular air jet impingement heat transfer

Abstract

The purpose of this study is to determine the effect of pulsating frequencies on the local and average heat transfer characteristics of a heated circular air jet. Pulsation of the air jet was produced by a rotating cylinder valve mechanism at frequencies between 10 to 80 Hz. Flow stru c t u res of the heated steady and pulse single circular axisymmetric air jet velocity are measured using a calibrated hot-wire anemometer and presented in non-dimensionalized form. Reynolds number was set at 16 000, 23 300 and 32 000. The heat flux of the heated air jet impinging on the plate was measured using a heat flux sensor at different radial positions. Results obtained show that the average pulsed jet Nusselt number was higher than the average steady jet Nusselt number for all values of frequencies due to the higher localised heat transfer of the pulsing jet. This was the result of enhanced turbulence intensity due to pulsing the jet. The stagnation point heat transfer of the pulsed jet obtained was lower for the same fre q u e n c y range due to the small turbulent intensity at this position.