Drying of agricultural products is a good way to store wet products. In recent decades, using solar dryers has received much attention due to the environmental problems of using fossil fuels. However, one of the main problems of solar drying system is the low thermal efficiency and inhomogeneous distribution of temperature in the drying chamber. In this work, the increase of heat efficiency of flat plate collector has been investigated using phase change materials and air recirculation mechanism. Copper pipes containing phase change material, at the top of the collector plate vertically at three 5, 10 and 15 cm intervals. Drying process of Oleaster fruit was used to evaluate the drying performance of the solar dryer. The results revealed that using air recirculation system and thermal storage systems improved the drying efficiency and thermal efficiency it was about 43.42% and 16.75 %, respectively. The average thermal efficiency for distances of 5, 10 and 15 cm was 53.26, 54.89 and 56.29 %, respectively. Using return air flow increased the thermal efficiency at least 11.65 %. By economical optimization about 8.6 %. The best mathematical to predict the drying was Henderson and pabis. Moreover, the results indicated that applied CFD model predicted the thermal performance of the dryer at acceptable range (with low relative error 2.56 ± 0.32%). Based on the optimization process the proper arrangement of PCM tubes inside of the collector was obtained.
