The Effect of Roughness Geometries on Heat Transfer Enhancement in Solar Air Heater - A Review

Abstract

Artificial roughness applied on the absorber plate in the solar air heater is the most acclaimed method to improve thermal performance. Moreover it is required to understand how flow field is affected by particular roughness geometry with artificial roughness. This roughness creates turbulence in flowing air by disturbing laminar sub-layer as turbulence increases there in increament of heat transfer rate.Some distinguished roughness geometries have been compared on the basis of heat transfer enhancements, Nusselt number and friction factor correlations as function of system and operating parameters for predicting performance of the system having investigated type of roughness geometry.Arti?cial roughness in the form of ribs is a convenient method for enhancing thermal performance of solar air heaters.W shape rectangular ribs in discrete form with double passwill show the significant increase in heat transfer rate and friction loss over the smooth channel in the range of parameter of Renolds no 10000 to 12000, relative roughness height 0.043 to0.044, relative roughness pitch 10 to 12, angle of attack 60° to 70°.