Drying Kinetics of Hygroscopic Porous Materials Under Isothermal Conditions and the Use of a First‐Order Reaction Kinetic Model for Predicting Drying

Abstract

Drying curves have been obtained from bread samples using an isothermal drying apparatus designed and developed in our laboratory. Previous work showed that Fick's diffusion equation was shown only to predict drying time and not drying rate. The results showed that proper measurement of effective moisture diffusivity under isothermal conditions did not solve the problem of accurately predicting moisture transfer. A first‐order irreversible kinetic model was developed to predict moisture loss during isothermal drying by modeling evaporation during drying. The drying curves obtained from the isothermal drying experiments were analyzed to determine the first‐order rate constant. The first‐order rate constant at temperatures between 40 and 70°C ranged from 0.04 s−1 to 0.19 s−1, and the activation energy determined by Arrhenius analysis was 48.7 kJ/mol. The rate equation was shown to impressively predict drying of bread samples throughout the entire moisture range, from 0.9 to 0.002 g/g dry solid.