Non-isothermal moving-boundary model for food drying

Mathematical modeling of food drying represents a key research topic. Drying is one of the most used processes in food technology. It is a complex process in which water concentration changes are very often associated with volume and structural variations of materials. This phenomenon, known as shrinkage, limits the possibility of using classical transport models to obtain reliable results for drying process analysis and control. Drying is intrinsically a non-isothermal process, even when it is performed under “isothermal” conditions, meaning when the air temperature in the drying chamber is kept constant. Indeed, thermal inertial of food samples, as well as thermal effects due to water evaporation at the sample boundary, must be necessarily taken into account for a deep understanding of the process and a reliable estimate of the effective water diffusivity. Moreover, in many practical applications, food drying takes place in non-isothermal conditions. The isothermal moving-boundary model for food dehydration and shrinkage, recently proposed by Adrover et al. (2019b,c), is here improved to account for thermal effects. A convection-diffusion heat transport equation, accounting for heat transfer, water evaporation, and shrinkage at the sample surface, is added to the convection-diffusion water transport equation. Experimental dehydration curves, in continuous and intermittent conditions, are accurately predicted by the model with an effective water diffusivity Deff(T) depending exclusively on the local temperature. The non-isothermal model is successfully applied to experimental data of continuous and intermittent drying of Guava slices, reported by Chua et al. 2000a.