A Comprehensive Review on Roughness Geometries and Investigation Techniques Used in Artificially Roughened Solar Air Heaters

Abstract

Artificial roughness applied on the absorber plate is the most acclaimed method to improve thermal performance of solar air heaters at the cost of low to moderate friction penalty. Experimental investigations pertinent to distinct roughness geometries unfolds that the enhancement in heat transfer is accompanied by considerable rise in pumping power. In view of the fact, a designer needs to carefully examine shape and orientation of roughness elements in order to choose the best fit roughness geometry for intended application. Moreover it is required to understand how flow field is affected by particular roughness geometry so that direction of future researches could be conceived. So as to elucidate the useful findings an attempt has been made to review roughness geometries employed in solar air heaters. Some distinguished roughness geometries have been compared on the basis of heat transfer enhancements and thermohaydraulic performance to draw attention towards their usefulness for specific applications. Furthermore, light is thrown on different investigation techniques adopted for prediction of heat transfer and friction characteristics of artificially roughened solar air heaters to recognize features and limitations of each technique.