Adsorption-desorption flow of condensable vapors through mesoporous media:Network modeling and percolation theory

Flow of condensable vapors in mesoporous media is investigated theoreticall y and experimentally during adsorption and desorption processes. A typical permeability curve of a condensable vapor is strongly enhanced in the capil lary condensation region. This is because additional capillary pressure gra dients are imposed on the capillary-condensed pores, which act as "good" co nductors compared to the noncondensed pores, which are considered "poor" co nductors. The percolation scaling properties that hold for a system of "goo d" and "poor" conductors are confirmed for the cases examined. As the ratio of gas flow/capillary-enhanced flow decreases, the rise of permeability wi th pressure becomes sharper, The network connectivity has a strong impact o n the maximum permeability value and on the width of the scaling law region s. The contribution of surface flow does not affect the permeability in the peak region, but results in a shrinkage of the scaling law regions. During desorption, a marked hysteresis in the permeability curves is found and it is attributed only to thermodynamic hysteresis, The maximum permeability v alues in this case are higher and shifted to lower relative pressures. (C) 2000 Academic Press.