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.