Enhancement of the heat transfer rate in free convection solar air heater using pin shaped artificial roughness on absorber plate

The technique of artificial roughness is used by researcher to augment the heat transfer coefficient in force convection between the absorber and air in solar air heater. In the present paper, a new artificial roughness (pin shape protrusion) on the absorber plate was used to achieve the enhancement in heat transfer coefficient of free convection between absorber plate and air. A specially designed test rig was fabricated for experimental measurements, comprising of four sections of 0.48 � 0.07 � 2.0 m, to acquire data of four different cases. The conical pins were used with three different relative height roughness, e/Dh, = 0.01636, 0.0245 and 0.0327 and one standard smooth un-protrusion flat plate absorber was used as a basis for comparison. The data for from the four test rigs were recorded simultaneously. The measurements were carried out at five inclination angles 10°, 30°, 50°, 70°, and to get the optimum angle of operation for free convection solar air heater. The results show that the conical pin artificial roughness has enhanced the heat transfer rate of the solar air heater by up to 41 as compared to the un-protrusion absorber plate heat transfer rate in free convection solar air heater. The heat transfer rate and Nusselt number are highest for relative height roughness e/Dh = 0.0327. The optimum inclination angle was found to be 50 degrees, at which the solar air heater performed most efficiently. © 2006-2016 Asian Research Publishing Network (ARPN).