Water sorption isotherms and thermodynamic properties of pearl millet grain
2010
Goneli, André Luis Duarte | Corrêa, Paulo Cesar | de Oliveira, Gabriel Henrique Horta | Gomes, Cassandra Ferreira | Botelho, Fernando Mendes
The water sorption isotherms of pearl millet grain and the thermodynamic properties obtaining during the process of drying pearl millet were examined. Equilibrium moisture content (Xeq) was determined under several temperature (T) and relative humidity (RH) conditions. The Xeq data were correlated by six mathematical models. The modified Henderson was the model that best fitted the experimental data. The Xeq decreased with an increase in T at constant RH. Hysteresis was also studied; increasing T led to a decrease in this phenomenon. Integral isosteric heat of sorption (Qst), differential entropy (ΔS) and the enthalpy-entropy compensation theory were studied. Qst values decreased when Xeq increased because the Qst values of adsorption were lower than Qst desorption values. The values of ΔS decreased with increases in Xeq, because ΔS values were higher for desorption than for adsorption. The enthalpy-entropy compensation theory is valid for describing the water sorption processes of pearl millet grain.
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