Development of an active solar crop dryer - Design analysis and performance evaluation

A forced convection Indirect solar dryer powered by a PVC module was designed and evaluated. The performance of the dryer was poor; its drying rate, collector and system drying efficiency were 0.74 kg/day, 12% and 10%, respectively. The dryer was redesigned and modified into a direct forced convection type. Its design analysis and performance evaluation was undertaken by drying marshed cassava. The drying rate, system drying, collector and pick-up efficiencies were 1.6 kg/day (14%/day), 9%, 46% and 29%, respectively. Comparatively, the drying rate for sun-drying was 0.9 kg/day. The collector efficiency compared very well to the designed value of 48% and may not need further improvement. The pick-up efficiency also compared well with typical averages for this type dryer. The drying rate and system drying efficiency indicate the need for further development of this dryer. Prediction equations were developed from the results of measured differences in collector, dryer and ambient air temperatures and plotted on graphs. It is recommended that the volumetric air-flow rate across the drying unit should be improved by the fan speed and air inlet area of the dryer. The improved dryer will subsequently be compared to a natural convection dryer so that an appropriate dryer technology can be recommended for the rural small-scale farmers.