Water migration and diffusion mechanism in the wheat drying

The understanding of the mutual migration behavior and water diffusion mechanism of different water components inside wheat granules is crucial for drying process selection and process parameter determination. In this study, the binding forms of water in wheat granules and the migration and diffusion characteristics of different water components during drying processes were studied on the basis of low-field nuclear magnetic resonance and magnetic resonance imaging. In the early drying stage, the internal water migration rate of wheat granules was larger than the external water evaporation rate. The drying rate was mainly dominated by the external water evaporation rate. In the middle drying stage, the internal water migration rate changed from larger than to less than the external water evaporation rate. The internal water migration rate gradually became the main control factor of the drying rate. During the drying process, the relationship among different bound water was a “parallel connection,” and the relationship between bound and free water was a “series connection.” In this study, the relationship between the activation energy and the different water components was obtained, and the Arrhenius-type expression of the effective moisture diffusivity was presented.