Influence of Air Flow Recirculation on Energy Consumption and Efficiency in a Solar Dryer

A mixed solar dryer with a specific mechanism to vary the tilted angle of collector، is utilized to fulfill all tests. The efficiency of the dryers is low because of various reasons such as heat loss of air in an open flow circuit. Getting air back toward the air inlet of dryer can increase the efficiency of dryer and decrease drying process period. A new mechanism considered for dryer which controls the percentage of air recirculation. It contains two dampers which embedded in return air channel of dryer. In order to investigate the effect of air recirculation on energy consumption of drying and dryer efficiency، thin layer of tomato slices are dried in three levels of air flow rate (0. 018، 0. 036 and 0. 054 m3/s) and four levels of air recirculation percentage (0، 50، 75 and 87. 5%). Total experiments were achieved in the beginning of autumn season to reach the moisture content of 12% (w. b) of the samples. The results illustrated the minimum of energy consumption and the maximum of efficiency was provided when 75% of air flow was got back to the inlet of dryer.