Energy and Exergy Evaluation Using Corrugated Multi-Ducts and Twisted Tape Inserts Applied to a Solar Air Heater: Experimental Research

An extensive experimental investigation was performed on the thermal, exergetic, and thermo-hydraulic performance of a corrugated multi-duct solar air heater (SAH) incorporating constrained twisted tape inserts under real outdoor conditions. A photovoltaic (PV)-powered DC blower was employed to supply the airflow, and four setups were tested: a smooth absorber plate, corrugated ducts, and corrugated ducts with one or two twisted tape inserts. The Reynolds number ranged from 2000 to 10,000. The results indicate that the configuration with two twisted tape inserts achieved the highest value of thermal efficiency under optimal operating conditions, with the useful heat gain increasing from about 100 W for the smooth case to 456 W. The Nusselt number increased by approximately 82% at low Reynolds numbers and 74% at high Reynolds numbers compared to the smooth configuration. Despite the related increase in the flow resistance, the thermo-hydraulic performance has improved significantly, with the thermo-hydraulic performance factor (THPF) reaching a highest value of about 1.9. Exergy analysis under optimal conditions revealed a maximum exergy efficiency of about 10.5% and a reduction in exergy destruction of approximately 9.7% compared to the smooth configuration. Furthermore, based on the experimental findings, empirical correlations for the Nusselt number and friction factor (FF) have been developed, and they show a strong agreement with the measured results, where the coefficient of determination (R²) values reach 0.97 and the mean absolute percentage error (MAPE) values are below 5%, which validates the reliability of the proposed model for real SAH applications.