A comparative study of performance of natural convection solar dryers

Natural convection solar dryers have the advantages of low investment, as compared to mechanical dryers, and minimize the problems associated with open sun drying. A variety of natural convection solar dryers are available world-wide, however identification of the most appropriate and economic design always poses a big challenge to the experts. This paper presents experimental evaluation of performance of three types of natural convection dryers. The tests were conductecd in Dar es Salaam, Tanzania during the days when the solar radiation intensity was between 325 W/m(2) and 480 W/m(2). Test samples of cassava with initial moisture content 76.5% (wt/wt wet basis) were dried to 9.5% final moisture content. The effective drying hours for this performance were about 14 hours, 18 hours and 20 hours in the mixed mode dryer, indirect dryer, and direct dryer respectively, while for the open sun drying the time taken was about 28 hours. The drying time was cut by half using the mixed mode dryer that showed comparatively better performance.