Analysis of thermal performance and drying kinetics of indirect solar drying under natural and forced convection

Abstract

Solar drying offers an effective and sustainable method for preserving agricultural products, particularly in regions with limited access to conventional energy. This study evaluates the performance of an Indirect-Type Solar Dryer (ITSD) for drying Bitter Gourd Slices (BGS), comparing natural and forced convection modes. The ITSD system comprises a V-grooved absorber solar collector, aluminium-finned paraffin wax as thermal storage, a drying chamber, and a blower operating at 0.064 kg/s for forced convection. Natural convection airflow ranged from 0.019 to 0.033 kg/s. Key performance indicators, including collector and dryer efficiencies, drying kinetics, Specific Energy Consumption (SEC), and Specific Moisture Extraction Rate (SMER), were experimentally analyzed. Mathematical modelling was applied to describe and predict the drying behaviour of BGS, offering insight into moisture removal dynamics. The average exit air temperature from the collector was 40.33 °C for natural convection and 38.76 °C for forced convection, with a higher temperature in natural convection due to lower airflow. Moisture content was reduced from 92 % to 12 % (wet basis) in 15 h under natural convection and in 12 h under forced convection. System efficiencies averaged 18.13 % and 19.35 % for natural and forced modes, respectively. SEC and SMER were 12.22 kW-h/kg and 0.084 kg/kW-h for natural, and 13.14 kW-h/kg and 0.079 kg/kW-h for forced convection. Despite higher air temperature in natural convection, forced convection demonstrated superior overall drying performance and is thus recommended for food processing applications where controlled and uniform drying is essential.