Performance Evaluation of New Combination External Recycle Flow and Arc-shaped Wire as Artificial Roughness of Solar Air Heater

The challenge of energy and environmental pollution has forced researchers to make more use of solar energy. In the present study, a new solar air heater collector system with a synthetic combination of arc-shaped wire roughness and external recycle of airflow has been presented, and its performance has been evaluated in different conditions. Modeling is performed using energy conservation equations for different parts of the collector and is solved by a semi-analytical method. The validation of the present results indicates the accuracy of the method used. The results showed that the new hybrid system effectively increased energy and exergy efficiencies at mass flows less than about 0.04 kg/s. Also, in a constant roughness condition and at low mass flow rates, increasing the flow recycle ratio to about 3, increased the collector performance.  However, in high flow rates and recycle ratios, exergy efficiency was reduced sharply due to high pressure drop, despite an increase in energy efficiency. Thus, it was less than the simple collector system. Increasing the intensity of solar radiation increased energy and exergy efficiencies in the new system. Examination of the geometric parameters of artificial roughness showed that an increase in the diameter of the curved wire improved the performance of the new system while changing the curvature angle of the wire had little effect.