Experimental study and mathematical modeling of thin layer drying of rhubarb (Rheum ribes L.)

In this study rhubarb stem slices were dried as single layers with thickness of 3 mm in the inlet air temperature range of 50-70  and air velocity of 1 ± 0.2 m/s in a laboratory scale cabinet dryer. The effect of drying air temperature on the drying characteristics was determined and the relationship between the drying parameters with temperature and moisture content was examined. Moisture transfer from rhubarbs slices was described by applying the Fick’s diffusion model. The effective diffusivity changes between 4.56×10-11 and 15.97×10-11 m2/s within the given temperature range and as the temperature increased so did the effective moisture diffusivity.  An Arrhenius relation with activation energy values of 57.4638 kJ/mol expressed the effect of temperature on the diffusivity. The experimental moisture loss data were fitted through 10 thin-layer drying models available in the literature. The models were compared based on the coefficient of determination, mean bias error, root mean square error, and the reduced chi-square between the observed and predicted moisture ratios. The Midilli et al. model has shown a better fit to the experimental drying data as compared to other models.