Drying kinetics and thermodynamic properties of pigeon pea beans

Resumo

Pigeon pea is a common plant cultivated in family farming. It is often used as a source of protein for animal breeding. The knowledge of the drying kinetics and the thermodynamic properties of pigeon pea beans (Cajanus cajan) is relevant for simulation of drying, which aims to maintain the quality of beans. The objective of this study is to estimate the drying curves of pigeon pea beans using mathematical models. This study also aims to deter­mine their thermodynamic properties. Forced-drying greenhouses were used for the drying process. The initial water content of pigeon pea beans was 1.00 dry basis (db). Beans were weighed periodically until reaching a near equilibrium water content. Ten mathematical models were fitted to experimental data to characterize drying pro­cesses using the following statistical criteria: coefficient of determination (R²), mean relative error (P), mean standard error (SE), chi-square (χ²), and residue distribution. From the selected model and the Arrhenius equa­tion, the effective diffusion coefficient and the activation energy used for the calculation of the enthalpy, entropy and Gibbs free energy were obtained. The Midilli was the best model to represent the kinetics of drying of pigeon pea beans. The increase in drying air temperature increases Gibs free energy and diffusivity, decreases enthalpy, and maintains the entropy negative.