Effect of Diffusion Path Lengths on Effective Moisture Diffusivity and Activation Energy of Red Delicious Apple Slices Under Convective Drying

The study analyzed the effect of diffusion path lengths (initial, average, and final half-thicknesses) on the shrinkage, effective moisture diffusivity, activation energy, and pre-exponential factor of thin-layer red delicious apple slices under convective drying conditions (temperature from 40 °C to 80 °C at 10 h drying time). The results show that the shrinkage increased from 31.09% at 40 °C to a maximum of 42.65% at 70 °C, then slightly decreased to 36.77% at 80 °C, indicating that shrinkage did not increase linearly with drying temperature. The diffusion path lengths yielded effective moisture diffusivities ranging from 1.43 × 10−10 to 10.31 × 10−10 m2/s, with the average characteristic length providing the most realistic representation of the effective moisture diffusivity. The high coefficient of determination (R2 = 0.965), consistent with the model efficiency value, confirms that the Arrhenius model fits the experimental diffusivity data across the temperature range studied. The mean absolute percentage error of 12% between the experimental and predicted diffusivities confirms the reliability of Fick’s and Arrhenius models. The activation energy ranged from 21.56 to 26.03 kJ/mol across diffusion path lengths, indicating a moderate sensitivity of moisture diffusion to temperature.