Multi-objective optimization and performance analysis of solar air heater for drying applications with s-type arc-shaped ribs

Solar air heaters are among the most promising renewable energy technologies for sustainable thermal energy production. Although artificial roughness elements have been widely used to improve heat transfer, comprehensive optimization studies considering S-shaped rib configurations and their practical application in drying processes remain limited. Therefore, this study presents a comprehensive thermo-hydraulic optimization approach for a solar air heater equipped with S-shaped arc ribs and evaluates its suitability for drying applications. Three arc radius, three rib-to-collector length ratios (P/L), and three discrete arc spacing ratios (G/H) were investigated within a Reynolds number range of 5000–15000. The experimental design was generated using Design-Expert software, while numerical analyses were performed using computational fluid dynamics in ANSYS Fluent. Response surface methodology was applied for multi-objective optimization, and the influence of design parameters on Nusselt number ratio, friction factor ration, and outlet temperature was evaluated. The optimal design parameters for achieving the maximum outlet temperature are R = 50, Re = 5000, P/L = 0.3, and G/H = 0.133. Accordingly, N u / N u 0 = 1 . 7 9 8 , f ⁡ / f 0 = 5 . 0 5 4 , and an outlet temperature of 309.553 were obtained. The collector with the highest thermo-hydraulic performance achieved a value of 2.89, whereas the collector with the maximum outlet temperature exhibited a lower performance value of 1.06, indicating an inverse relationship between outlet temperature and overall thermal enhancement ratio. The proposed methodology integrates thermo-hydraulic optimization with application-oriented evaluation, providing valuable design guidelines for the development of efficient solar-assisted drying systems. Based on the obtained temperature, aromatic herbs were identified as the most suitable drying products.