Design and performance of a dual-function mixed-mode solar dryer with heat recovery for grapes drying: A 4E and sustainability study

This study summarizes the design, fabrication, and extensive assessment of an innovative mixed-mode solar dryer (MMSD) equipped with a heat recovery system to enable effective drying of red grapes under climatic conditions of Gujarat, India. The system features a UV-stabilized, semi-hemispherical drying chamber coupled with a polyvinyl-coated solar air heater operating under forced convection. This hybrid configuration simultaneously facilitates agricultural drying and preheating of saline water for potable water production through solar distillation, effectively addressing energy efficiency and water scarcity challenges in arid regions. Experimental results showed an appreciable enhancement in performance over conventional open sun drying, as indicated by more than 60 % reduction in drying time, consistent operational performance, and better product quality. The system reached an optimal thermal efficiency of 35.79 % with a corresponding optimum exergy efficiency of 7.6 %, demonstrating its remarkable energy performance. Drying kinetics were well represented using the Simplified Fick's Diffusion model (R2 = 0.99987). The economic analysis revealed a feasible payback period of 2.3 years, alongside a reduction of 1.73 tons in CO₂ emissions, coupled with estimated carbon credit savings of about USD 394.97 over the system life cycle. Therefore, the integrated MMSD presents itself as a scalable, economically competitive, and environmentally friendly technology suitable for implementation in water-scarce remote localities.