Thermal Performance Investigation of a Single Pass Solar Air Heater

Abstract

AbstractOne of the most promising energy sources being utilized in much direct and indirect processes of energy conversion is solar energy, of which solar air heaters are the foremost application of direct use of solar energy. Solar air heaters use air as a medium for thermal conduction; however, air has low thermal conductivity resulting in lower heat transfer coefficient absorber plate and the medium of air. Artificial roughness induced by ribs reduces thermal resistance by breaking the viscous sublayer while promoting turbulence to increase the coefficient of heat transfer. In the present work, evaluation of the performance of conventional solar air heater with an absorber plate containing V-shaped ribs has been done. V-shaped ribs have been used on absorber plate at the relative roughness pitch of 10 and an optimum value of relative roughness height of 0.02, with 45° as angle of attack. The values for solar insolation and Reynolds number are varied from 600 to 1200 W/m2 and 5000 to 20,000, respectively. The results show an enhancement in Nusselt number of ribbed duct from 1.9 to 2.25 times as compared to a smooth duct. The use of ribs on absorber plate has significantly increased the efficiency by about 7.75–18.33%. However, the variation in outlet temperature with increasing Reynolds number is less significant for lower values in contrast to the higher values of solar insolation. The variation of overall loss coefficient, thermal efficiency and useful heat gain is also studied for the range of operational scenarios. KeywordsSolar air heatersReynolds numberSolar fluxUseful heat gainHeat transfer coefficients