Development of a multi-purpose solar tunnel dryer for use in humid tropics

Particularly in tropical countries, a high percentage of crops are spoiled during the drying period due to permanently high relative humidity and sudden rainfalls. Open air sun drying and smoke drying, which are traditional drying methods in these regions, lead to insufficient product quality. In order to be marketable, the produce meant for sale on the world market has to meet high quality standards. Otherwise the price will decline resulting in low profits for the exporting country and the producing farmer. To produce high quality products for the world market as well as to reduce losses, the development of suitable dryers for tropical regions is urgently needed. A multi-purpose solar tunnel dryer, orginally developed for the use in arid zones, was modified to enable operation under tropical weather conditions. This type of dryer consists of a small centrifugal blower, a collector and a tunnel drying chamber. To prevent penetration of water into the construction and subsequent flooding, the solar dryer was installed on a wooden substructure. To heat the drying air during cloudy and rainy days, particularly in the rainy season, a biomass furnace with heat exchanger was integrated into the solar drying system. The construction consists exclusively of materials available in Java. Only low energy requirements are necessary to run the blower. Results showed that compared to natural sun drying, the drying time of cocoa, coffee and coconut could be reduced up to 40%. Solar drying improves the quality of the products in terms of colour, flavour and appearance, reduces the risk of microorganism growth, prevents insect infestation and contamination by foreign matters and mycotoxins. The products dried with the solar drying system meet the national and ingternational market standards. Investigations further showed that even during the rainy season it was possible to dry the products to the final moisture content which is needed for storage and marketing. The modular system allows adaptation to different farm sizes as well as cooperative use.