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

Modelling of the food drying process is dependent on the understanding of the complex moisture transport mechanisms. This study analyzed the effect of drying temperatures ranging from 40 to 80 °C and diffusion path lengths (initial, average and final half-thicknesses) on the shrinkage, effective moisture diffusivity and activation energy of thin-layer red delicious apple samples under convective drying. Fick’s second law and Arrhenius model were utilized to determine the effective moisture diffusivity and activation energy. The mean shrinkage increased from 31.09% at 40 °C to a maximum of 42.65% at 70, then slightly decreased to 36.77% at 80 °C, indicating that shrinkage does not increase linearly with drying temperature. The initial, average and final half-thicknesses yielded effective moisture diffusivities ranging from 1.43×10–10 m2/s to 1.03×10–09 m2/s, with the average dimension providing the most realistic representation of the effective moisture diffusion path during drying. The linear regression models between the natural logarithm of the moisture ratio and drying time showed a strong fit with R2 values ranging from 0.9955 to 0.9971, confirming the reliability of Fick’s second law for describing the effective moisture diffusivity. The mean activation energy ranged from 21.56 to 26.03 kJ/mol across the different characteristic lengths, indicating the minimum energy requirement for moisture diffusion in red delicious apple samples during the convective drying.