Drying rates of some fruits and vegetables with passive solar dryers

Abstract

Two passive solar dryers were designed and constructed with available local materials. The passive solar dryers which were direct and indirect types were tested with pepper (Capsicum annum L.), okro (Abelmoschus esculentus L.) and vegetables (Amaranthus hybridus L.) in order to evaluate the drying rate of these produces. The moisture content of 78.9% (w.b.) for 180 g freshly harvested peppers was reduced to 24.0% (w.b.). The drying rate in the direct passive solar dryer was found to be higher than the indirect passive solar dryer. The initial moisture content of 92% (w.b.) for 1000 g okro was reduced to 20% (w.b.). The drying rate in the direct passive solar dryer was also found to be higher than in the indirect passive solar dryer. The initial moisture content of 90% (w.b.) for 400 g vegetable was reduced to 20% (w.b.). The drying rate with the direct passive solar dryer was found to be higher than that with indirect passive solar dryer. During the course of drying, after each crop was kept inside the drying system, the temperature of the drying was monitored at an-hour interval; the moisture content was also monitored at a three-hour interval until there was no more change in the weight of the crop. The crops dried faster with the direct passive solar dryer than with the indirect passive solar dryer. As a result of the highest temperature attained in the direct passive solar dryer, the rate of moisture removal was the highest in this dryer.