The low-density diffusion coefficient of soft-sphere fluids in nanopores: Accurate correlations from exact theory and criteria for applicability of the Knudsen model

Bonilla, Mauricio Rincon and Bhatia, Suresh K. (2011) The low-density diffusion coefficient of soft-sphere fluids in nanopores: Accurate correlations from exact theory and criteria for applicability of the Knudsen model. Journal of Membrane Science, 382 1-2: 339-349. doi:10.1016/j.memsci.2011.08.033


Author Bonilla, Mauricio Rincon
Bhatia, Suresh K.
Title The low-density diffusion coefficient of soft-sphere fluids in nanopores: Accurate correlations from exact theory and criteria for applicability of the Knudsen model
Journal name Journal of Membrane Science   Check publisher's open access policy
ISSN 0376-7388
1873-3123
Publication date 2011-10-15
Sub-type Article (original research)
DOI 10.1016/j.memsci.2011.08.033
Volume 382
Issue 1-2
Start page 339
End page 349
Total pages 11
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2012
Language eng
Abstract Molecular transport in confined spaces is of central importance to many traditional and emerging applications, such as gas separation and storage, catalytic and non-catalytic fluid–solid reactions and nanofluidics. The classical method to model the influence of solid–fluid particles collisions in transport comes from the early works of Knudsen and Smoluchowski, in which van-der-Walls interactions are neglected. While such assumption may be adequate for wide channels or high temperatures, it has been shown to lead to significant overprediction of the low-density diffusion coefficient in narrow pores at low and moderate temperatures, when compared to that obtained through molecular dynamics simulations. However, while molecular dynamics offers a much more accurate route for the calculation of diffusivities, its implementation and use is time-consuming and the Knudsen formulation remains preferred, particularly for interpretation of experimental permeation data. On the other hand, the oscillator model, developed in recent years in this laboratory, provides a straightforward method to estimate the low-density diffusivity, taking into account the dispersive forces exerted by the wall through rigorous statistical–mechanical considerations. The computational demand of the oscillator model is several orders of magnitude lower than that of a typical molecular dynamics run, though much greater than that of the simple Knudsen formulation. In order to facilitate its use, we provide several simple correlations for the fast estimation of the oscillator model-based diffusion coefficient for LJ fluids in simple geometries, as a function of the pore size and the LJ fluid–solid interaction parameters. Moreover, the parameter values for which the Knudsen equation supplies a reasonable estimation of the diffusion coefficient are presented for various degrees of accuracy.
Keyword Diffusion in porous media
Adsorption
Knudsen diffusion
Gas separation
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
Official 2012 Collection
 
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