Development of a novel solar dryer with an incorporated heat exchanger

Abstract

This study analyzes the thermal performance of an indirect-type solar dryer incorporated with a heat exchanger to recover heat from the exhaust. Data were recorded for 8 h from 9:00 to 17:00 from November to January to determine the drying rate for varying airflows from 2 l/s to 12 l/s under the weather conditions of Nepal and Bhutan. The air temperatures in multiple locations in the dryer were recorded and logged for 30-second intervals. The results indicated that incorporating a simple heat exchanger can achieve 78 % and 81 % effectiveness for the lowest tested airflow of 2.5 l/s and 2 l/s in Nepal and Bhutan. The heat transfer effectiveness increases with decreasing flow, resulting in a higher cold side outlet temperature of the heat exchanger for lower airflows. The solar air collector demonstrated efficient performance, achieving 80 % and 90 % efficiencies for the highest tested airflows of 12 l/s and 10 l/s in Nepal and Bhutan, respectively. Due to an increased heat transfer coefficient, the incoming air can effectively remove the accumulated heat from the absorber plate for higher airflows. The drying rates were observed to be the highest for 12 l/s, with a value of 85 g/(h × m2) for apples and 10 l/s, with a value of 56 g/(h × m2) for gingers in Nepal and Bhutan, respectively. From both cases, it can be concluded that the highest tested airflows provide higher air circulation for effective heat and mass transfer from the product to the surrounding air for drying.