Modeling and thermodynamic properties of the drying of tamarind (Tamarindus indica L.) seeds ¹

Modelagem e propriedades termodinâmicas da secagem de sementes de tamarindo (Tamarindus indica L.)

ABSTRACT

In the present study, the objective was to fit different models to the experimental data of drying of tamarind (Tamarindus indica L.) seeds and to select the best model, to determine the effective diffusion coefficient, activation energy and thermodynamic properties for the process during drying at different temperatures. The experiment was carried out at the Laboratory of Post-Harvest of Vegetable Products of the Instituto Federal Goiano (Federal Institute Goiano) - Campus of Rio Verde, GO, Brazil. Seeds with initial moisture content of 18 ± 0.25% dry basis were oven dried with forced air ventilation, at controlled temperatures of 45, 60, 75 and 90 °C in four repetitions. Nonlinear regression models used to describe the phenomenon were fitted to the experimental data. To represent the drying of tamarind seeds, the Midilli model was selected for the range from 45 to 60 ºC and the Two terms model was selected for the range from 75 to 90 ºC. The effective diffusion coefficient increases with the increase of drying air temperature, being described by the Arrhenius equation, with activation energy of 35.16 kJ mol^-1. Enthalpy and entropy decreases, while Gibbs free energy increases with increasing drying temperature.

Key words:
Two terms Model; Midilli Model; Gibbs free energy