Design of an Apparatus for Solar Drying of Farm Products

A large part of crops is discarded due to their high production volume, and the small local market covered. Besides, commercialization of some crops is seasonal. Crops with a high content of water are perishable in a short time, so it is necessary to implement technological alternatives in order to preserve these products. One way to make better use of crops with high water content is by getting dehydrated products. The conversion of solar radiation into thermal energy for dehydration of crops is a widely known practice in agroindustry. Tropical regions receiving high solar radiation intensity are appropriate for the dehydration of crops in solar dryers. This process has proven effective for the upgrading of farm crops, and diversification of final products that may be destined for local and international market. The present work is developed as a response to the priority needs for small local farm crops that are not financially supported by government royalties, in a tropical country located in South America. The solar dehydrator described here is a modular unit to be used in non electrically interconnected zones (NIZ), and built with local materials, that makes use of convective heat to remove the moisture of previously sliced farm products. This way, this study covers the development of a simple agroindustrial process focused on the upgrading of crops, the broadening of marketing alternatives and the use of renewable energy sources. Two crops are considered as case studies for the solar dehydration: mangoes and tomatoes. Data required for the design calculations (density, moisture, solar radiation, temperature and humidity of air) were obtained experimentally, and from databases developed by governmental institutions. Microbiological analysis (total coliforms, fecal coliforms, enumeration of aerobic mesophilic microorganisms, molds and yeasts) were carried on samples before and after dehydration tests, to evaluate the adequacy of the dried products for human consumption. The results show that the solar dehydration is a feasible approach for preserving crops with a high content of water, in the region considered for this study; however, some crops require to be pre-treated before drying, due to the tendency of bacteria growth during or after the process.