Vol. 3, Issue 6, Part E (2017)

Abstract
The heat transfer coefficient of a smooth surface is quite low in an air heater. This is due to the formation of laminar sub layer. To break this formation of layer artificial roughness in the form of projections in the underside of absorber plate is used. In this way heat transfer rate can be enhanced. In the present paper multiple arcs with gap is used in the form of artificial roughness for a better efficiency. The experiments were conducted at Reynolds number of 11000. The outlet air temperature of modified duct was higher than that of smooth duct. There has been use of oil in the form of thermal storage that starts showing its result after 4:00 pm when solar radiation starts decreasing. In this way an extra 2.5 hours of time was utilised i.e. up to about 06:00 pm. In the beginning of reading from 11:00 am to 2:00 pm the outlet air temperature of smooth surface was higher than roughened surface. But even as the solar radiation starts diminishing a higher air temperature was still received at the outlet of roughened surface due to the release of heat from oil heat storage. Thus, it is observed that use of oil enhance the effectiveness of solar air heater.