Capillary models for porous media. VIII. A study of gaseous flow in the transition from the Knudsen to the Poiseuille flow regimes

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Abstract
For pt.VII see ibid., vol.10, p.2423 (1977). The capillary network model has been used to examine the effects of connectivity and radius distribution on the minimum in the transition from Knudsen to Poiseuille flow. It was found that, using formulae for infinitely long capillaries, the minimum persisted in two-dimensional random networks for all the structures examined. When short-tube formulae were used to describe the flow in network elements minima were absent even when the length to (mean) radius ratio was as large as 20. It is concluded that the limitation of diffusion path lengths, rather than network topology, is the significant factor influencing the Knudsen minimum. On the other hand, information about network structure can be obtained from structure factors at low- and high-pressure limits.