The article presents a mathematical model of drying that describes the kinetics of combined microwave-convective drying for the process as a whole. Based on this model, the drying curves and the temperature evolutions of the drying body were constructed by a number of computer-simulated drying programs, which were chosen to follow the respective experimental processes carried out on a cylindrical sample made of kaolin. The experimental data allowed both the estimate of material coefficients arising in the model and the validation of the theory. A very satisfactory correlation of the theoretical predictions with the experimental data is found. The main novelty of this article is the mathematically complete drying model that describes all periods of the microwave-convective drying process. Application of such a complete model is necessary if we want to optimize drying processes with respect to drying time and consumption of energy via computer simulations.

The aim of this article is to present a self-consistent mathematical model describing the heat and mass transfer phenomena during the convective drying both in the constant and in the falling drying rate periods. This general model is developed on the basis of the theory of mixtures and the thermodynamics of irreversible processes. The boundary conditions are formulated and the numerical algorithm enabling calculation of the temperature and the drying curves in the two mentioned periods of drying is constructed. In this paper much effort is devoted to the experimental validation of the model. The convective drying of a cylindrical sample made of kaolin was examined both experimentally and numerically for comparison and the distribution of temperature and the drying curves were determined. A very good agreement of the experimental and theoretical results is stated.

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