Comparative Experimental Investigation of Corrugated Solar Air Heater Using Porous Media and Twisted Tapes

This experimental work examines the thermal, thermohydraulic, and exergetic performance of a modified revised multi duct solar air heater (SAH) under real outdoor conditions. Four configurations were examined, including a smooth collector, ducts with corrugation, porous-lined ducts, and corrugated ducts equipped with inserted twisted tapes over the investigated Reynolds number (Re) interval (2000–10,000). The airflow was supplied by a DC fan powered directly by photovoltaic modules. Introducing internal flow-modifying elements resulted in a marked enhancement of the SAH heat transfer capability, as confirmed by the experimental observations. When compared to the smooth absorber, among the tested configurations, the twisted tape configuration delivered the highest useful heat gain of approximately 456 W under peak operating conditions, which is a significant improvement. At Re = 10,000, the Nusselt number (Nu) increased from 39.3 for the smooth collector to around 148.35 for the porous-lined ducts and roughly 108 for the twisted tape arrangement, showing the substantial impact of surface modification and flow disruption on heat transfer by convection. The overall thermo-hydraulic performance significantly improved even though the redesigned configurations lead to an increase in frictional losses; at higher Re, the thermohydraulic performance factor (THPF) reached a maximum value of about 1.651. A maximum exergy efficiency of about 10.45% was obtained from the exergy analysis conducted under peak operation conditions, but the exergy destruction was lower in comparison to smooth absorber. Also, from experimental data empirical correlations were calculated for friction factor (f) and Nu, and they demonstrated a high degree of agreement with the results that were observed. The findings indicate that passive flow modification techniques can significantly improve the SAH's thermal and exergetic performance for relevant renewable energy applications.