Heat Transfer Augmentation of a Solar Air Heater Using a Twisted V-Shaped Staggered Rib Over the Absorber Plate

Abstract

An effort is made to study the performance of a solar air heater having the absorber surface roughened by providing staggered, twisted V-shaped ribs roughness. Liquid crystal thermography technique is applied to get the Nu distribution over the surface. Experimentation is done for Reynolds number ranges from 3000 to 21000, relative roughness to pitch ratio (P/e) from 7 to 11 and relative staggered distance (d/e) of 2 to 6, for fixed angle of attack (a), relative twist length (y/e), relative roughness length (S/e). It is found that maximum Nusselt number and friction factor augmentation is of 3.43 and 2.57 times than that of smooth duct. The maximum thermo-hydraulic performance (THP) value obtained is of 2.69 for the P/e of 9 and d/e of 4. It can be inferred that staggered twisted V-shaped rib roughness helps to get the enhanced Nu with minimum friction penalty.