Multiscale aspects of heat and mass transfer during drying

The macroscopic formulation of coupled heat and mass transfer has been widely used during the past two decades to model and simulate the drying of one single piece of product, including the case of internal vaporization. However, more often than expected, the macroscopic approach fails and several scales have to be considered at the same time. This paper is devoted to multiscale approaches to transfer in porous media, with particular attention to drying. The change of scale, namely homogenization, is presented first and used as a generic approach able to supply parameter values to the macroscopic formulation. The need for a real multiscale approach is then exemplified by some experimental observations. Such an approach is required as soon as thermodynamic equilibrium is not ensured at the microscopic scale. A stepwise presentation is proposed to formulate such situations.