Experimental and numerical study of combined effect of PCM and artificial roughness on energy, exergy, and enviro-economic (4E) analysis of double pass solar air heaters

Solar air heaters (SAHs) are widely utilized in applications such as greenhouse conditioning, crop drying, and space heating; however, conventional systems often suffer from low thermal efficiency and limited heat storage capability. To address these limitations, this study investigates a novel double-pass solar air heater (DPSAH) integrated with phase change material (PCM) OM_48 and V-shaped artificial roughness to enhance both heat transfer and latent thermal storage. The experimental setup was evaluated under controlled artificial solar radiation of 1000 W/m 2 for a range of Reynolds numbers (Re = 4000–16000). In parallel, Computational Fluid Dynamics (CFD) simulations were performed using the RNG k–ε turbulence model to analyse flow behaviour and transient heat transfer within the PCM domain under constant radiative conditions, providing detailed insights into the temperature distribution and thermal response of the system. The PCM was analyse using characterizations to confirm a melting temperature of 48-51 °C and stable organic composition with carbonyl (C=O) and hydroxyl (OH) functional groups suitable for thermal storage. The results indicated that the PCM-integrated roughened absorber achieved an average increase of 87% in thermal efficiency and 62.42% in exergy efficiency compared to a smooth duct without PCM. The system stored up to 140 kJ of thermal energy, enabling continuous heat discharge for 4.5–5 h after radiation cutoff. Economic assessment revealed that the system provided 959.4 kWh of Annual Useful Energy (AUE) at a levelized cost of ₹12.8/kWh, with an exergoeconomic factor of 0.0067 kWh/INR and potential carbon credit earnings of ₹36,267.93.