Performance analysis of W-shaped rib roughened solar air heater

Abstract

Artificial rib roughness is a convenient method for enhancing thermal performance of solar air heater. An experimental investigation has been carried out to study the thermo-hydraulic performance of solar air heater using W-shaped ribs on absorber plate, the roughened wall being heated while the remaining three walls being insulated. W-shaped ribs have been tested both pointing downstream (W-down) and upstream (W-up) to the flow. The roughened wall has relative roughness height (e/Dh) of 0.03375, relative roughness pitch (p/e) of 10 and duct aspect ratio (B/H) of 8. The airflow rate corresponds to Reynolds number between 2300 and 14 000. The heat transfer results have been compared with those for smooth duct under similar flow and thermal boundary condition. Thermo-hydraulic performance ratio of roughened absorber plate by providing W-shape roughness is in the range of 1.46–1.95 for W-down and 1.21–1.73 for W-up ribs. Friction factor and heat transfer coefficient correlations have been developed based on the law of wall similarity and heat-momentum transfer analogy.