The paper presents a detailed mathematical model for performance prediction of a smooth duct solar air heater validated against the experimental results. Experimental study on a solar air heater having absorber plate with half-perforated baffles on the air flow side shows thermal efficiency enhancement of 28%-45% over that of the smooth duct solar air heater, which is attributed to the heat transfer enhancement (of the order of 180%-235%) due to the perforated baffles attached to the absorber plate and reduction in the mean temperature of the absorber plate by 20• C-25• C as compared to the temperature of absorber plate of smooth duct air heater. Using the mathematical model, the performance plot for the baffled duct air heater has been presented, and the effect of the variation of ambient parameters on the predicted thermal efficiency has been studied.

Heat transfer is measured in a rectangular channel with detach transverse square ribs using liquid crystal thermography. The ribs were provided on one broad wall of rectangular duct of aspect ratio 4. The roughened surface was heated uniformly. The roughness parameters selected for this study were, relative roughness pitch (P/e) of values 7-11, clearance ratio (C/e) of values 0.37-0.57 and Reynolds number (Re) of values 8100-22300. The heat transfer coefficient has been compared with attached transverse square ribs at similar operating condition and result reveals that detach rib roughness is better than the attach ribs. It is observed that the thermal performance parameter increases with increase in Reynolds number.