Performance enhancement of solar air heater using hybrid methods: Focused review on current progress,challenges,and future opportunities with ribs,jets,and nanocoatings

Abstract

The improvement of solar air heater (SAH) performance has gained greater importance with the increasing demand for clean thermal energy. This review discusses the main techniques for increasing their efficiency, including jet impingement for targeted heat transfer, adding ribs for creating local turbulence, and nanocoating for improved thermal and optical properties. Ribs significantly increase the heat transfer by 2-6 times with thermo-hydraulic performance parameter (THPP) values rising to 3.4; however, at the expense of increased friction and pumping power. Jet impingement enhances heat exchange, achieving THPP values of 3.5-4.1, but with considerable pressure losses and auxiliary power requirements. In contrast, the nanocoating increases the thermal efficiency by 8–25% and raises the outlet temperature by 5-20°C with negligible hydraulic penalties. The review covers experimental and computational fluid dynamics (CFD) studies, durability investigations, and optimization strategies. Although these techniques have been established effectively in laboratory-scale tests and confirmed by CFD analyses, their incorporation into commercial SAHs has been low. To date, applications are mostly limited to prototype systems; recent techno-economic analysis indicates payback periods ranging from 0.3 to 6 years and annual CO₂ emission reduction of up to 0.7-44 tons. Future research efforts have been proposed, including the shift to field validation, design of hybrid systems, long-term performance observation, and techno-economic studies, to enable large-scale implementation and make next-generation solar air heaters feasible and cost-effective.