Impingement Heat Transfer Due to Circular Air Jet Over Rough Flat Surfaces

Abstract

An experimental investigation was carried out to investigate the pressure distribution and the local and average Nusselt number due to impinging of a circular air jet over uniformly heated rough flat surfaces. The present investigation shows the dependence of the pressure on jet exit Reynolds number, relative roughness of the surfaces and nozzle-to-surface spacings. It was observed that the overall pressure coefficient, cp increases with the increase of jet exit Reynolds number and decreases with the increase of surface roughness and nozzle-to-surface spacings. It also observed that the coefficient pressure at the stagnation point remains constant for the lower values of surface roughness but increases beyond a specific value of surface roughness.

In this investigation the nature of dependence of heat transfer on various parameters namely, jet exit Reynolds number, relative roughness of the surface and nozzle-to-surface spacings are identified Jet exit Reynolds numbers of 6000. 8700. 16520 and 23400 , relative surface roughness of smooth. 0.01306, 0.01338, 0.01806. and 0.01952 and dimensionless nozzle-to-surface spacings of 1.61. 2.41, 3.22. and 4.03 are considered for the investigation. It was observed that the local Nusselt number increases with the increase of jet exit Reynolds number and surface roughness, but decreases with the increase of nozzle-to-surface spacings. It also observed that the stagnation point Nusselt number remains constant for the lower values of surface roughness but increases beyond a specific value of surface roughness, which predicts that there is a critical value of surface roughness. The average Nusselt number was calculated and a correlation developed in terms of jet Reynolds number, relative roughness of the surface and nozzle-to-surface spacings. The correlation yields ±10% accurately in context with experimental findings, however shows singularity for smooth surface. Experimental results provided useflul intbrmatiofl which have significant of potential industrial applications regarding the radius of the heat transfer area, nozzle-to-surface spacing atid surface roughness for maximizing the average Nusselt number.