Development of A Pore-Scale Model

In the macroscopic description of porous media, structural features are hidden in effective parameters, and phenomena that are characteristic of the micro-scale are obscured by rather crude, often semi-empirical, models. Of course, this general deficiency is also true for the macroscopic description of gel drying. However, the transition to the second drying period, and in particular the development of cracks at this moment, is a particular problem, where the necessity to account for pore-scale phenomena becomes even more evident. The purely macroscopic description needs criteria that not only depend on the microstructure itself, but also on how it behaves during drying. 

When the liquid/gas phase boundary recedes into the gel, the spatial distribution of liquid and solid is crucial for the mechanical load on the gel by capillary forces and the ability of the gel network to support this load without damage. In order to 

In a first model version, the liquid distribution on the network of primary particles is assumed to be in capillary equilibrium. This allows interpretation of the fluid dynamics problem as a shape transformation problem. Cormected liquid patches have uniform curvature K of the liquid/gas phase boundary additionally, at three-phase boundaries, the contact angle 6 to the solid surface must be fulfilled (see Fig. 5.44). 

The drying problem is solved in small time steps by removing some liquid at the local evaporation rates and subsequently relaxing the liquid with a volume-of-fluid approach as proposed by Stepanek et al. (1999). Space is discretized into voxels, and the distribution of solid, liquid and gas is described by the respective volume fractions in these voxels (, Jw and ). From these phase functions, normal vectors can be computed, for example 

Understanding and Preventing Structural Changes During Drying of Cels 

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