Thermo-hydraulic performance enhancement of solar air heater (SAH) having multiple arcs with gap shaped roughness element on absorber plate

Abstract

The present paper studies the thermal performance of solar air heater which is artificially roughened by providing multiple arcs with gap shaped roughness element. As thermal efficiency of smooth collector is quite low, hence there is a need to augment heat transfer from the absorbing surface. The experimentation has been carried out for Reynolds number (Re) ranges from 2100- 21000, relative roughness height (e/D) of 0.044, relative roughness pitch (p/e) of 8, relative gap distance (d/x) range of 0.25- 0.85, relative roughness width (W/w) ranges from 1-7, relative gap width (g/e) range of 0.5-2 and arc angle (a) of 60°. The thermal efficiency is found to be best for relative gap distance (d/x), relative gap width (g/e) and relative roughness width (W/w) values are 0.65, 1.0 and 5 respectively.

Keywords: Solar air heater; Nusselt number; thermal efficiency; multiple arcs with gap; roughened