Effect of the Absorber Plat Groove Roughness on Performance of Solar Air Heaters

Abstract

An experimental investigation on heat and fluid flow characteristics of fully developed turbulent flow in a rectangular duct having repeated integral transverse chamfered rib-groove roughness on one broad wall has been carried out. The flow Reynolds number of the duct varied in the range of approximately 3000–21000, most suitable for solar air heater. Experimentation has been done on chamfered rib-groove roughness having 60° V groove varying relative roughness pitch of 4.5, 6, 7, 8 and 10, chamfer angle of 5°, 12°, 15°, 18°, 22° and 30°, relative groove position of 0.3, 0.4, 0.5 and 0.6, and relative roughness pitch of 0.022, 0.03, 0.35 and 0.04. The effect of roughness parameters on thermo-hydraulic performance parameter index has been studied experimentally and optimized. The maximum thermo-hydraulic performance parameter index for chamfered rib-groove roughened surface is observed of about 2.08 for the relative roughness pitch of 6, relative groove position of 0.4 and chamfer angle of 18° for relative roughness height of 0.04. The thermo-hydraulic performance parameter index of the chamfer rib-grooved surface compared with the square ribbed, chamfered rib, square rib-grooved surface. It can be seen that the thermo-hydraulic performance parameter for chamfered rib-groove roughness is the highest for the Reynolds number lower than about 12000, which is most suitable for solar air heater.