Theoretical Study for Apple Slice Drying in Superheated Steam

A theoretical model for superheated steam drying of apple slice is presented, in which the spatial distributions of temperature and moisture inside the product layer are considered. The model is built based on the diffusion theory in which the effective diffusivity is a function of moisture content and it is calculated by fitting with experimental data. There is good agreement between the experimental moisture content and the simulated average moisture content. The moisture and temperature distributions show that the moisture gradient is high while the temperature gradient is small. Moisture content on the surface reduces dramatically at the beginning of drying while this at the center spends several minutes to start to evaporate. Temperatures witnesses the constant period corresponding with the first drying stage then temperature increases continuously to the gas temperature. Results of the study can be used for simulating for dryer scale in the computational fluid dynamics in the next step.