Modeling and Experimental Analysis of a Dual-collector Indirect Solar Dryer for Intermittent and Continuous Drying of Bioproducts

Abstract

This study presents the development and experimental validation of a coupled heat and mass transfer model for a dual-collector indirect solar dryer based on the energy balance of a representative section of the system. The governing equations describe the simultaneous evolution of collector temperature, drying air temperature and product moisture content while accounting for solar irradiance variations of up to 1050 W m⁻², convective heat transfer and both continuous and intermittent drying modes. Experimental tests were conducted on banana (Musa paradisiaca) and sweet potato (Ipomoea batatas), with a loading capacity of 1.5 kg for each product and an intermittency ratio of α = 0.5 under a controlled drying temperature below 60 °C. Temperature profiles, dry-basis moisture content and drying rates were determined and analysed for both operating configurations. The results showed favourable thermal conditions for drying, characterised by a gradual increase in temperature and enhanced mass transfer during the initial drying stage. Moisture content decreased from approximately 1.4 to 1.2 kg water kg⁻¹ dry matter for banana and from 3.0 to 2.6 kg water kg⁻¹ dry matter for sweet potato, indicating rapid evaporation of free water. Maximum drying rates of 5.6 and 6.3 kg water kg⁻¹ dry matter min⁻¹ were recorded for banana and sweet potato, respectively, demonstrating the intensity of heat and mass transfer at the beginning of the process. Comparison of continuous and intermittent drying modes showed that intermittency reduced the overall drying rate while stabilising thermal and moisture gradients. Numerical predictions were in good agreement with experimental observations, confirming the reliability of the proposed model. The observed discrepancies were mainly attributed to climatic fluctuations and simplifying assumptions adopted in the model.