DEVELOPMENT AND PERFORMANCE EVALUATION OF A FORCED CONVECTION SOLAR DRYER

Abstract

Natural sun drying has many drawbacks which include direct exposure to sunlight, pests and rodents and lack of proper monitoring of the drying process. Solar dryers have been investigated to overcome these problems. A forced convection solar drying system was developed using local materials and tested. The dryer consist of a solar collector flat plate, solar panel, battery, drying chamber and fans. The solar collector is laid with black stone pebbles, which serve as heat storage materials medium in order to maintain constant air temperature inside the dryer. The air allowed in through air inlet is heated up in the solar collector and channelled into the drying chamber. The maximum drying temperature through the drying time was 39°C. The dryer was used to dry fresh tomato slices. It was able to reduce the moisture content of 400 g sliced tomatoes from 72% to 10% (dry basis) in 26 hours of effective dehydration time. The amount of the moisture content decreases base on drying temperature and the time of exposure to sun radiation. The highest temperature (39°C) of the outlet solar collector has been obtained at 1:00 pm at radiation intensity, 812W/m². The maximum temperature attained in the drying chamber was 39⁰C which was 6⁰C greater than maximum ambient temperature of 33⁰C. The efficiency of the solar collector was calculated to be 68.7%, while the efficiency of the solar collector without incorporating fans was calculated to be 78.5%. The thermal efficiency of the solar dryer with fan during the test period was found to be 47.3%, while the efficiency of the solar dryer without the fan during the test period was found to be 50.8%. The relative humidity decreased as temperature increases, but it was higher in the dryer than the atmosphere as a result of the amount of moist air been removed from the food material when fans are used. The maximum dryer efficiency was found to be 71.25% and the minimum was 35.14%, while the maximum efficiency of the dryer without fan during the test period was found to be 61.79% and the minimum was 14.75% due to atmospheric condition