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The diffusion equation in discontinuous systems

Authors
Journal
Physica
0031-8914
Publisher
Elsevier
Publication Date
Volume
50
Issue
3
Identifiers
DOI: 10.1016/0031-8914(70)90257-0
Disciplines
  • Physics

Abstract

Abstract The coefficients expressing the effects of gradients in composition, pressure, and temperature, and of external forces, on normal diffusion in discontinuous systems are derived. Non-equilibrium thermodynamics is used to state the form of the diffusion equation and to simplify the kinetic-theory calculations of its coefficients. It is found that the pressure-diffusion and forced-diffusion effects are significantly affected by the presence of kinetic boundary layers and by gas-surface interaction. Finally, explicit expressions are obtained in terms of the masses, molecular diameters, and accommodation coefficients for tangential momentum, and the physical interpretation of the result is given.

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