Abstract
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.
Highlights
With the growing search for alternative sources of fuels, oil crops such as peanut (Arachis hypogaea L.) can gain even more space in the Brazilian economic scenario
Peanuts are harvested with unsuitable water content for storage
The use of drying process to reduce the water content of this agricultural product is essential for its conservation
Summary
With the growing search for alternative sources of fuels, oil crops such as peanut (Arachis hypogaea L.) can gain even more space in the Brazilian economic scenario. With the possibility of using peanut oil as a raw material for the production of biodiesel, it is important to study the pre-processing of this product, aiming at the conservation and maintenance of the same in this stage of the production chain. Peanuts are harvested with unsuitable water content for storage. In this sense, the use of drying process to reduce the water content of this agricultural product is essential for its conservation. For the study of drying systems, mathematical simulations based on the drying of successive thin layers of the product are carried out. For the drying of products in thin layer, mathematical models are used to represent the water reduction of the material in function of time, being them theoretical, semi-theoretical and empirical
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