Experimental Energy–Exergy–Economic–Environmental Assessment of a Curvature–Vortex-Intensified Serpentine Solar Air Heater for Low-Carbon Thermal Applications

Enhancing convective heat transfer in solar air heaters (SAHs) without disproportionate hydraulic penalty remains critical for decentralized low-carbon heating. This study experimentally investigates a serpentine-channel SAH equipped with distributed three-dimensional vortex generators under outdoor winter conditions. The configuration combines curvature-induced secondary motion with distributed vortex generation to intensify absorber–air heat transfer. Experiments were conducted over a mass flow range of 0.012–0.061 kg s−1, corresponding to a Reynolds number range of 2.1 × 103–1.07 × 104, using a smooth duct as the reference configuration. The enhanced configuration achieved peak thermal efficiencies of 81.6–85.4%, compared with 65.8–67.7% for the smooth collector, while daily averaged efficiency increased from 56–59% to 71–75%. Although pressure drop increased, thermo-hydraulic performance remained superior across the investigated Reynolds number range. Exergy efficiency was consistently higher for the enhanced system and remained within optical limit constraints. Environmental assessment based on grid emission factor displacement indicates approximately 33% greater annual CO2 mitigation potential, corresponding to about 6.6 tonnes over a 20-year service life. The levelized cost of heating was estimated at 3.1–4.4 ₹ kWh−1. These results indicate that compound curvature–vortex transport intensification can improve thermal efficiency and increase carbon mitigation potential under realistic operating conditions.