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Permeability of gases in porous media is a vital parameter for the design of landfill liners and buffers for nuclear waste repositories, gas extraction from petroleum reservoirs and hydrate bearing sediments, vapor extraction to decontaminate soils, carbon dioxide sequestration, etc. It is well understood that the gas-phase permeability in porous media is predominantly governed by the porosity, pore-characteristics (viz., diameter and distribution), properties of the gas (viz., density, molecular size and weight, sorption capacity, and viscosity) and their state of saturation (Sr). However, the nature of the flow of gas (viz., molecular, viscous and Knudsen), is influenced by the mean free-path, its compressibility and mean diameter of the pores. All these factors and complexities pose a challenge in determining the intrinsic permeability, K, which otherwise is assumed to be a (i) constant and (ii) fingerprint of porous media. In this context, and to facilitate easier determination of the gas-phase permeability, Kg, of porous media, a test setup: Gas Conductivity Measuring device, GasCoM, has been developed. Efforts have also been made to understand the influence of the characteristics of the gas (viz., active, inert, non-polar, monoatomic, diatomic and mixture of several gases) on Kg of different porous media (viz., soils of entirely different physico-chemical-mineralogical characteristics compacted at different densities and saturation, and commercially available alumina discs, referred to as standard porous media, SPM). A critical synthesis of the experimental data reveals that the flow of gas in porous media gets significantly influenced by (a) the hygroscopic moisture content, which also highlights the importance of its mineralogy and (b) its tortuosity. Furthermore, a correlation that can be employed for estimation of the Kg, for various gas-porous media systems, GPMSs, has been proposed and validated by using experimentally obtained results. |
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