Evaluation of Performance of a Solar Tunnel Crop Dryer in Drying of Two African Indigenous Vegetables (AIVs)

Abstract

Two AIVs dried were the black night shade (solanum scabrum) and the spider plant (cleome gynandra) and were spread as a thin layer on the tray during the drying processes. The tray carrying the vegetable was placed next to the outlet section of the dryer and the side towards the inlet was left bare to act as absorber plate to preheat air before passing over the drying product. The hot air from the free absorber plate supplement the heat absorbed directly by the product from the solar radiation penetrating through the transparent cover hence enhances the drying rate. The results show that the area has over six hours of peak solar hours (6 PSH) when insolation is over 1000 W/m²; hence the site has sufficient solar energy to dry up the vegetables. The average efficiency of the dryer was determined as 24.3% and the moisture content of the spider vegetable was reduced from 88.4% to 21.0% in 2 days while that of black night shade reduced from 84.5% to 26.3%  in 3 days. In addition, the drying profiles of the two vegetables consisted of four stages, with drying rates varying from 4.3 g/hr to 22.4 g/hr for spider vegetable and 2.4 g/hr to 23.7 g/hr in black night shade. Hence, the prototype dryer proved to be effective in drying both vegetables and has a relatively good efficiency.