Experimental Evaluation of Exergetic and Sustainability Performances in Solar Air Heaters Using Transverse Wire Rib Roughness With Various Gaps

Abstract This experimental study was conducted under real-time outdoor weather conditions at a site in India (latitude 19.1008 deg N, longitude 81.9818 deg E) to evaluate the second law (exergetic) efficiency of roughened solar air heaters (SAHs) using transverse wire ribs with various gap numbers (Ng = 1–4) against a smooth duct. The analysis focused on exergetic performance indicators, including exergy input (Exin), exergy output (Exout), exergy destruction (Exdest), exergetic efficiency (ηII), improvement potential (IP), and the sustainability index, with results compared against existing literature. Five SAH configurations types I–V were tested at different air mass flow-rates (m˙) ranging from 0.01891 to 0.03937 kg/s, with relative roughness pitch (P/e = 10), relative roughness height (e/D = 0.043), and duct dimensions (360 mm width, 30 mm height). The configuration with Ng = 2 at a mass flow-rate (m˙) of 0.02889 kg/s yielded the best performance, recording the highest Exin (426.57 W), Exout (9.89 W), and exergetic efficiency (3.54%). The maximum exergy destruction (422.58 W) occurred at Ng = 3 and 4, while the highest IP (418.90 W) was observed at the highest flow-rate, and the peak sustainability index (1.03669) again occurred at Ng = 2. The comparative analysis confirms that the roughened configurations notably outperform the smooth duct and show improvements over results reported in prior studies, underlining their practical potential for sustainable energy applications.