Cinética de secagem e propriedades termodinâmicas da polpa de trapiá

Abstract

ABSTRACT The objective of the research was to study the drying of trapiá pulp with the addition of drying aids, determining the drying kinetics and thermodynamic properties of the samples. Formulations of the pulp was treated with the additives monoglycerides, carboxymethylcellulose - CMC and guar gum in different combinations and concentrations (F1 - 0.5% CMC and 0.5% Monoglycerides; F2 - 0.5% Guar Gum and 0.5% Monoglycerides; and F3 - 0.25% Guar Gum, 0.5% CMC and 0.5% Monoglycerides) trapiá. Drying was carried out at 50, 60 and 70 ºC with 0.5 cm thick layers. The drying kinetics were determined, and different mathematical models fitted to the data. The Midilli model best represented the drying kinetics, with determination coefficients ≥ 0.9985. The effective diffusivities increased with increase in temperature with magnitudes to the order of 10-10 m2 s-1. The enthalpy variations (ΔH) reduced with increase in temperature and were positive. The entropy variations (ΔS) were negative and inversely proportional to the temperature. The variation in Gibbs free energy (ΔG) was positive and increased with increase in temperature.