RESULTS AND DISCUSSIONS duration. Therefore, mixed mode solar cabinet dryer which using the passive drying air flow rate is the best drying method. Using the dryer in the best selected conditions (natural convection in the mixed mode state), reduced the moisture content of the product from 43.5% to 4.95% after 90 min.
Thin layers (10mm thickness) of Cuminum cyminum grains were dried in the solar cabinet dryer. Four levels of air flow rates [three active air flow rates and one passive]
50 Thermal efficiency of solar collector was determined in three levels of active drying air flow rate. Inlet air temperature to the solar collector and outlet air temperature from it as well as solar radiation intensity was used to determine the thermal efficiency of solar collector. Variation of solar radiation intensity versus drying time has been shown in Figure5 for different levels of active drying air flow rate. Thermal efficiency of the flat plate solar collector is calculated as formula (1). Average solar radiation intensity was used in each air flow rate to determine the efficiency of collector. Air mass flow rates
0 20 40 60 80 100
Drying time(min)
Fig. 4: Drying rate of Cuminum cyminum grains in two drying modes for passive drying air flow rate equivalent to the volume air flow rates were obtained from standard heat transfer tables. Finally, the thermal efficiency was calculated as shown in Figure6. The higher is the drying air flow rate the higher is the thermal efficiency. It may be due to; in the highest drying air flow rate the transferred heat to the air from absorber plate is