Coupled transport and poromechanics model to understand quality evolution during sequential drying

Abstract

Sequential drying provides opportunities to achieve quality by combining individual drying modes. Many process and product parameters affecting multiple drying modes make it complex. We studied quality evolution in a sequence of microwave, impingement, and hot air drying of the mashed vegetable chip using a poromechanics and transport model with volumetric evaporation, moisture-based microwave absorption, pressure-driven expansion, moisture loss-driven shrinkage and glass transition. It was validated for temperature, moisture, size and porosity obtained in an industrial setting. Gas porosity is higher at the center during microwave and at the surface during impingement drying. Moisture loss-driven shrinkage was more dominant than pressure-driven expansion. Shrinkage followed the moisture loss when the chip was rubbery, but shrinkage reduced after the glass transition occurred. Sequential drying was able to achieve a quality that would be hard to achieve using a single drying method. The mechanistic framework, successful for three drying modes and their sequence, is useful to understand drying-like processes.