Mathematical Modeling on Air Drying of Apples Considering Shrinkage and Variable Diffusion Coefficient

In this study, a mathematical model was developed to describe the drying kinetics of apple samples in a hot air dryer. The model takes into consideration material shrinkage and moisture- and temperature-dependent diffusion coefficients. This model is capable of predicting the changes in moisture content and temperature with and without shrinkage inside the samples. The results of the model were compared with the experimental data to investigate the importance of shrinkage phenomena and effective diffusion coefficient on the drying kinetics. Disc-shaped apple samples were dried under air conditions at temperatures in the range of 60 to 80 degrees C and the shrinkage of samples was measured experimentally. The results showed that the shrinkage had a significant effect on the effective diffusion coefficient and consequently affected the moisture and temperature distribution inside the material. Finally, a statistical analysis was performed and good agreement was found between the predicted and experimental results.