Modeling of Moisture Distribution in Thin Layer Drying Process

Apple slices were dried with hot air and combined microwave hot air drying methods in an microwave dryer, the apple slices were prepared as single layer with thickness of 5, external and internal diameter 60 and 20 mm respectively. The effect of drying air temperature and microwave power on the drying characteristics were determined. It was found that apple slices would dry perfectly within 30-54 min under convective conditions and 27-48 min under microwave-convective conditions. The transport of water during dehydration was described by applying the Fick s diffusion model and the effective diffusivity changed between 2.39*10-9 and 4.14*10 -9 m2/s in convective method. A non-linear regression procedure was used to fit 5 thin layer drying models available in the literature to the experimental drying curves. The models were compared using the coefficient of determination, mean relative percent error, root mean square error and SSE. The 3rd Degree polynomial model has shown a better fit to the experimental drying data as compared to other models. Finally, this paper presents a developed mathematical model for predicting transport phenomena in drying process of apple slices.