Fractal Phase Distribution and Drying: Impact on Two-Phase Zone Scaling and Drying Time Scale Dependence.

Abstract

In an article published in 2008, Professor A.R. Mujumdar and his colleagues reviewed some applications of fractal concept on drying. As a modest continuation to this article, we give an overview on three drying-related issues where fractal aspects are present. First, we discuss within the framework of the theory of invasion percolation in a gradient the characteristic lengths that determine the extent of the hydraulically connected region during drying. It is pointed out that the scaling of this region is fundamentally different in 2D and in 3D, owing to the different percolation properties in 2D and 3D. In particular, it is shown that the fractal region only represents a small region of a drying front in 3D systems. Then a situation is described where fractal porous structures form as a result of an evaporation process. Finally, we consider drying in systems characterized by an initial fractal distribution of the liquid phase (invasion percolation cluster), a situation expected to happen in PEM fuel cells, and explore the size-dependent property of the overall drying time from pore network simulations.