MICROSCOPIC DETERMINATION OF TRANSPORT PARAMETERS IN DRYING POROUS-MEDIA

The flow and distribution of liquid and vapor in the pore space of drying porous media are represented by a simple network model that incorporates the microscopic mechanisms. A method akin to Monte Carlo and molecular dynamics approaches is described for calculating from any such model the macroscopic, 'volume-averaged,' or effective transport parameters: relative permeabilities for pressure-driven flow, effective diffusivities for molecular diffusion, and so on. The method is to map representative small samples of pore space onto regular networks that have equivalent mean coordination and are made up of biconical pore segments intersecting in pore bodies, all dimensions being drawn from measured or estimated distributions. Evaporation and meniscus curvature, vapor movement by diffusion away from menisci and viscous flow toward them are described by one-dimensional local approximations. The resulting large set of ordinary differential and algebraic equations is solved by computer. Solutions from several such realizations are averaged to determine relative permeability to liquid, capillary pressure, and effective diffusivity of vapor as functions of liquid saturation and drying history. The results are to be used for interpreting, interpolating, and extrapolating experimental measurements of the same quantities.