Development and Performance Evaluation of a Natural Convection Indirect Solar Dryer

Abstract

The performance of a natural convection indirect solar dryer using enhanced collector design which would minimize heat losses has been investigated in this work. The collector is the non-porous type in which the absorber plate is cooled by air stream flowing on both sides of the plate. Following (Tiwari, 2002), a glass wool insulation of about 5 cm thickness was used on the sides of the collector to minimize conduction heat losses from the sides. An optimum gag width of about 2.5 cm is used for the collector (Madhusudan et al. 1981). Actual performance testing was carried out in Minna, a West-Central Nigerian town with the annual average of daily global solar radiation of around 5.5 kWh/m2/day and annual average of daily sunshine hours of about 8 hrs/day (Iloeje, 2004), an environmental condition typical of the entire North Central region of the country. Experimental test-drying of 20 kg fresh tomato reduces the moisture content from the initial 95.24% wb to the final 10% wb in 48 hours, equivalent to six drying days. The overall thermal efficiency was obtained as 42.44%.