Computer-aided sizing of direct mode natural convection solar crop dryers

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Ghana is an agricultural country. Most crops are seasonal and the need to dry them for preservation and utilisation throughout the year is imperative. The Ministry of Food and Agriculture has formulated a policy aimed at promoting simple solar dryers for drying agriculture produce with the view of reducing post-harvest losses which are currently 20- 30 % of the country’s annual food production. There is the need to design simple but effective drying systems suitable for varied crops and different geographical locations. Currently, there are no simple tools that enable the realisation of optimum design and quick sizing of solar crop dryers suitable for Ghana and similar climatic conditions. The aim of this research is to develop a user friendly computer program that could be used to generate dimensions and other design parameters. One major achievement of this study is the development of a set of governing equations and a solution procedure for sizing solar cabinet and tent crop dryers. Also a computer program based on this procedure has been developed. The program enables the sizing of solar cabinet and tent dryers suitable for drying of cassava, maize, cowpea, and rice in four geographical locations in Ghana. The four locations are Accra, Kumasi, Takoradi and Tamale. A sample result of the computer program is presented in this thesis. It appears, after analysing the results that, cassava can be used as the base crop for sizing dryers for drying the four crops listed. The limitations of this study are based on the assumptions. Firstly, the air leaving the dryer is assumed saturated. In practice, this is difficult to achieve. That minimizes the dimensions of the dryer. Secondly, the equation that gives the temperature elevation inside the dryer has been assumed true for solar cabinet and tent dryers; though it was deduced empirically from solar air heaters. At last, the shrinkage, which is the diminishing of the crop volume as moisture is removed in the drying process, has been neglected. This assumption can be a good approximation for low moisture content crops like cowpea, rice and maize; but, for high moisture content crop like cassava, the shrinkage effect has to be investigated.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfillment of the requirement for the award of the degree of Master of Science in Mechanical Engineering, 2003