Experimental investigation and mathematical modeling of the unsteady drying kinetics of durum wheat grains

Abstract

Dehydration of durum wheat often occurs under conditions where the effects the drying temperature, the water activity and the elasticity of the grains are significant to influence the drying kinetics. We here investigate the unsteady isothermal desorption process of a moisture from durum wheat grains by employing the static gravimetric method conducted at 30°C and 40°C and at controlled relative humidity values of 6.26% and 74.7%. Moreover, to explain our measured data, we have derived a new elastic diffusion model that extends Fick’s laws by taking into account the effect of the elasticity of the deformable grains. To consider the grain shrinkage during dehydration, we express the diffusion governing equation into the “grain material” coordinates system. We discuss in more detail the unidirectional radial mass transfer via scaling analysis and numerical solutions followed by a successful comparison between the model predictions and our measured data. A diffusion-elasticity coupling constant  emerges naturally in the diffusion equation and its effects on the drying kinetics as well as on the grain radius retraction are examined. We found out that the elasticity enhances mass transport within the investigated grains and thus decreases the drying time.