2018 Volume 61 Issue 8 Pages 539-543
In application of one dimensional diffusion theory to gas molecular flow in the steady state through long ducts of uniform cross section, diffusion coefficient 𝒟 is generally represented as
here λ is a kind of mean free path and v is avarage velocity of molecules. Up to now rigorous expressions of λ＝λS where λS is Smoluchowski's expression for λ which have been given by Smoluchowski himself and other author for rectangular, ellipsoidal and annular cross section. As for triangular cross section, the rigorous expression has been obtained only on equilatera-triangle cross section. In this report, the concrete expression of λS and the correction factor α defined by the ratio of λS/λK where λK is Knudsen's expression for λ, are deduced for long ducts with isosceles-triangle cross sections. The values for λS and α, which are given by these deduced formula, are compared with those obtained from the Monte-Carlo simulation, which uses the mean free path in the duct ℓ and the mean square of free path in the axial direction of the duct .