The Effect of Mass Flow Rate and Time of Crop Discharge, on the Rate of Rough Rice Drying in Semi-continuous Solar Dryer

The application of solar energy for drying cereals and other agricultural commodities has been increasing lately. This is due to the fact that solar energy is free, renewable, inexhaustible and environmentally friendly. This research is a new approach for employing solar energy as the main energy source for drying purposes. The drying test rig was designed, fabricated and evaluated. The grain solar dryer is an active mixed mode type with a semi-continuous discharge system. The rig consists of six solar air collectors, a heating channel, a drying chamber and an air distributing system. Rough rice was selected as cereal grain to be dried in the dryer to evaluate the system of the drying rig. In this research the effect of mass flow rate and time of crop discharge, on the rate of crop drying were evaluated. The experiment was conducted as a factorial experiment on the basis of a completely randomized design with three replications. The first factor was mass flow rate at three levels of 0.011, 0.0066 and 0.0048 kg/m2s and the second factor was the time of crop discharge at two levels of 15 and 30 min. The dryer capacity, the amount of energy consumed (electrical and solar) during drying process, and the efficiency of collectors were also evaluated. According to Duncan's multiples range test, the effects of mass flow rate of drying air, and the interval time of discharge, were highly significant on the moisture content of discharged rough rice. The maximum efficiency of the collectors was 37.13% and the fraction of energy consumed by heating channel during the drying process, compared with solar energy, was 6-8 percent. The maximum capacity of the dryer was about 132 kg of rough rice from 11 AM to 2 PM reducing the initial moisture content from 27% to 13%. On the whole, the evaluation results indicated that the dryer could reduce the moisture content of the crop to the storage safe moisture content during appropriate time with highenergy efficiency.