ABSTRACT:
The aim of this study was to adjust mathematical models to the experimental data on the peanut kernels drying in thin layer, as well as to determine the effective diffusion coefficient and the main thermodynamic properties involved in drying of the grains under different air conditions. The peanut kernels, with a water content of 0.59 ± 0.002 (dry basis, d.b.), were dried in a forced air ventilation oven with different temperature levels (40, 50, 60 and 70 °C) until reaching a water content of 0.04 ± 0.001 (d.b.). For the experimental data, eight mathematical models traditionally used to represent the drying kinetics of thin layer of agricultural products were adjusted, also being determined the effective diffusion coefficient and the thermodynamic properties, specific enthalpy and entropy and Gibbs free energy. The Diffusion Approximation, Two Terms, Midilli, Page and Thompson models represent the drying kinetics of peanut kernels in thin layers. The effective diffusivity increases with the increase of temperature, being the relation with the drying temperature described by the Arrhenius' equation. The increase in temperature promotes the decrease of the enthalpy and entropy values and the increase of the Gibbs free energy.
KEYWORDS:
Arachis hypogaea L.; effective diffusivity; activation energy; Page model; thermodynamic properties
