Design, Construction and Performance Evaluation of a Solar Drying System for Crops

Abstract

This research presents the design, construction, and analysis of the performance of a mixed-mode solar dryer for crops. A mixed-mode solar dryer utilizes direct solar radiation from the sun as well as input heat ducted from the solar collector inlet which is directly connected to the dryer. Such dryers have been shown to outperform passive solar dryers as it was also shown in this work using drying kinetics. Tomatoes were dried in the drying chamber under the mixed-mode condition. The maximum dryer temperature obtained was 39.2, while the lowest relative humidity in the dryer was 32%. These conditions are shown to be only fair for drying of tomatoes as it prolongs drying time. The system’s performance was largely affected by poor insolation and high heat losses during chosen drying days. Based on drying kinetics, a drying rate of 2.88units/day was obtained during the chosen drying days. With this rate, the dryer can dry 2kg of tomatoes within three days. The dryer can reduce the moisture content of 1kg of tomatoes from 95% to 14% within 45 hours of drying time. The capacity of the dryer is 1kg of products per tray. A simplified 2D transient heat transfer model of the temperature distribution in the drying chamber is presented. Results obtained show that material selection, insolation, and inlet temperature play a crucial role in the solar dryer performance.