ABSTRACT
Thermo-hydraulic performance comparison of various types of roughness geometries proposed for solar air heater ducts shows that the integral chamfered-with-groove roughness is the most preferred type. The performance studies of solar heaters with this preferred roughness on the air flow side of the absorber plate have been carried out for space heating applications corresponding to winter conditions in Jodhpur using a mathematical model. A comparison of the performance has also been made with a smooth duct collector.
Results of the study have been presented in the form of plots of thermal efficiency and effective efficiency (which considers the heat collection and pumping power together) versus the temperature rise parameter, and pumping power versus the flow rate, which can be utilized by designers. The effect of roughness and ambient parameters has been studied. The thermal efficiency of roughened collector is found to be significantly higher than smooth duct collector. Higher the height of the roughness elements, greater is the enhancement in the thermal efficiency. For air mass flow rate per unit area of absorber plate less than about 0.036 kg/sm2, the roughened duct collectors are also thermo-hydraulically better than smooth duct collectors.
