Orientation effects on laminar natural convection heat transfer from branching-fins

Abstract

The effect of orientation on the laminar natural convection heat transfer from branching fins attached to a rectangular plate has been numerically investigated. The orientations are termed ‘vBvF’ (vertical Base vertical Fin) and ‘hBvF’ (horizontal Base vertical Fin) when the base plate is vertical and horizontal respectively and the branching fins are attached orthogonally on the base plate. The third orientation is ‘vBhF’ (vertical Base horizontal Fin) when the fins are arranged horizontally on a vertical base plate. Besides orientation effect, the investigation also involves the effect of fin dimensions on the heat dissipation performance. Optimum branching angle of a ‘single’ branching fin is determined in each orientation. Fin size influences the optimum angle only in hBvF orientation. By studying the characteristics of buoyant fluid flow over the heat sinks, we have observed ‘vortex motion’, ‘geometry induced acceleration’ for certain sizes and orientations of the fins. These flow features are specific to the branching fins in natural convection. The dependency of the average heat transfer coefficient on the fin dimensions is explained and correlations to predict the Nusselt number in terms of non-dimensional parameters are developed. Highest thermal performance is obtained in vBvF orientation followed by hBvF and vBhF orientations. A comparison test has indicated that the branching fins have more effectiveness and efficiency than rectangular fins of equal mass and equal base area in all orientations.