Experimental and Mathematical Investigations of Apple Slices Convective Drying

The aim of this work was to determine sorption isotherms and thin layer convective drying behavior of apple slices and to compare the experimental and calculated results by using models available in the literature. The sorption isotherm was determined at four temperature levels 40, 50, 60 and 70 °C and at water activity ranging from 0.058 to 0.89, using the static gravimetric method. A non-linear regression procedure was used to fit experimental sorption isotherms and drying curves with most used empirical mathematical models available in literature. It was found that the Peleg model suitably represent the sorption experimental data in the mentioned investigated ranges of temperature and water activities. The Midilli et al. model satisfactorily described the thin layer drying behavior of apple slices. The drying characteristic curve and the thin layer drying rate expression of apple slices have been established from experimental convective drying kinetics. The values of the diffusivity coefficients at each condition were obtained using Fick's second law of diffusion. They varied from 8.51 × 10 -8 to 3.28 × 10 -7 m 2 /s in the temperature range of 40-70 °C and in the relative humidity range of 20%-40%. The activation energies for moisture diffusion were calculated to vary from 26.72 to 35.83 kJ/mol.