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, and V-shaped ribs roughness. The liquid crystal thermography technique is applied to get the Nu distribution over the surface. Experimentation is done for Reynolds number ranges from 3000 to 21,000, relative roughness to pitch ratio (P/e) from 7–11 and relative staggered distance (d/e) of 2–6, for the fixed angle of attack (α), relative twist length (y/e), and relative roughness length (S/e). It is found that the maximum Nusselt number and friction factor augmentation are 3.43 and 2.57 times than that of the smooth duct. The maximum thermo-hydraulic performance (THP) value obtained is 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.