Design fabrication and characterization of a solar food dryer for Palapye, Botswana

Abstract

Dehydration is a way to preserve food that may spoil. Drying removes water and thus prevents fermentation or the growth of molds. It also slows the chemical changes that take place naturally in foods as when fruit ripens. People in Botswana and the rest of the world have been drying food for thousands of years by placing the food on mats in the sun. This simple method, however, allows the food to be affected or ruined by dust, airborne molds and fungi, insects, rodents, and other animals. Furthermore, open air drying is often not possible in humid conditions. Solar food dryers represent a major improvement upon this ancient method of dehydrating foods. This study profiles the design, fabrication and performance evaluation of an indirect cabinet solar dryer. The dryer consists of a separate solar collector that heats up ambient air entering the collector and creates a convectional current that drives warm air into a coupled drying chamber. Food samples comprising tomatoes and apples were used for the performance evaluation of the dryer. The comparison experiment sought to differentiate the performance of the dryer from the largely uncontrolled natural drying i.e., direct sun drying. The results from the experiment showed that the temperature inside the drying chamber was consistently higher than the ambient air temperature. The drying rate of the dryer and percentage moisture loss content were 0.18 kg/hr and 91 % respectively. For natural drying the drying rate and percentage moisture loss were found to be 0.14 kg/hr and 71 % respectively. The dryer revealed its ability to dry products without them losing most of their original color as compared to direct sun drying as well as protecting products from birds, insects, strong winds and being soiled. Some of the open-air dry samples were eaten up by birds.