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Gas slippage in fractal porous material

Abstract:

Gas flow through porous media in the slip flow regime is of great significance for the exploitation of underground natural gas and oil. The gas slip effect in porous media plays a very important role in different engineering fields, because gas slippage is involved in the determination of gas apparent permeability. In this study, the gas slip effect was investigated in model microporous materials: composite silica aerogels. We measured gas and water permeability in sets of nano composite silica aerogels, fractal materials with a high pore volume and tortuosity, and low permeability. The observed difference in gas and water permeability was analyzed from the point of view of the slip regime (Klinkenberg correction), b) and transition regime (Knudsen correction). The effect of structural parameters of porous media (pore volume, tortuosity, fractal features) on the Klinkenberg and Knudsen corrections are discussed and the different models proposed in the literature are tested. Experimental results showed that: (1) gas permeability is almost two orders of magnitude greater than water permeability, (2) Klinkenberg and Knudsen corrections increase with decreasing permeability, (3) the Knudsen corrections calculated from the literature models were almost one order of magnitude lower than experimental data, (4) we also tested the Klinkenberg approach for tortuous and fractal porous media, the fractal model with second-order slip improved the accuracy of the pbkp_rediction and agree with the experimental results.