Experimental study on the solar drying of Rhubarb (Rheum ribes L.) with parabolic trough collector assisted with air recycling system, nanofluid and energy storage system

In the present work the thermo-economical calculation of dried Rhubarb slices in a dryer integrated parabolic trough solar collector assisted with air recycling mechanism and Al2O3 3.75 % as working fluid was investigated. Using air recycling system at the inlet section of the dryer and phase change material increases the thermal performance of the dryer and reduces the drying time of Rhubarb slices. Two adjustable valves at inlet and outlet part of the dryer and the amount of return flow was considered to control the airflow. In this study, the effect of air recycling flow at the inlet part of indirect chamber at four levels of 0–25–50–70 % was considered and the amount of specific energy consumption, total drying efficiency and solar collector efficiency was analyzed. To determine the performance of the system, Rhubarb slices in 5 mm as thin layer were used. In addition, CFD modeling was applied to predict temperature changes inside the dryer. The drying time decreased with increasing the recirculation of air, considerably. The overall drying efficiency increased about 2.32–8.21 %, and specific energy consumption decreased at least 1.91 % by applying air recycling mechanism, nanofluid and PCM in dryer related to the system without them. The exergy efficiency for drying of Rhubarb slices varies between 35.4 and 61.3 %. The optimization of the system was carried out based on the conditions and the result revealed this leads to decrease the payback time.