Flow and Heat Transfer Characteristics of Wall Jet over Rough Surfaces

Abstract

Experimental investigation were carried out to verify the pressure distribution and the local Nusselt number due to circular wall jet over uniformly heated rough flat surfaces. The present investigation shows the dependence of the pressure on jet exit Reynolds number and relative roughness of the surfaces. It was observed that the overall pressure co-efficient, Cp decreases with the increase of jet exit Reynolds number and also decreases with the increase of surface roughness. The present investigation shows the local Nusselt number distribution with various Reynolds number and relative roughness of the surfaces. Jet exit Reynolds numbers of 8799, 10777, 16849 and 18804 as well as relative surface roughness of smooth, 0.01371, 0.01435, 0.01581 and 0.01613 were considered for this investigation. The coefficient of pressure decreases with the increase of jet exit Reynolds number because of the fluid moving with higher kinetic energy initially and decays along the length of the surface due to frictional effect and decreases with the increase of relative surface roughness because the effect of friction increases with the increase of relative roughness. It was observed that the local Nusselt number increases with the increase of jet exit Reynolds number and also increases with the increase of surface roughness. Because of higher Reynolds number turbulence is generated in the laminar sub-layer, which is mixed in the buffer layer of the boundary layer. The average Nusselt number was calculated and a correlation developed in terms of jet Reynolds number and relative roughness of the surface. The correlation yields ± 10% accuracy with experimental findings. Experimental results provided useful information, which have significant and potential industrial applications regarding the heat transfer area and surface roughness for maximizing the average Nusselt number.