The problems of free-molecule gas flow in channels are abundant in modern technology in particular in vacuum engineering. The progress in nanotechnology has induced new investigations in the field of gas flow in nanoscale channels where the free-molecule flow regime is realized and surface diffusion of adsorbed molecules can essentially affect mass transfer. The paper deals with a theoretical study of the joint effect of the character of gas molecule scattering by channel wall and surface diffusion of adsorbed molecules on the channel permeability in the free-molecule flow regime. It is shown that the resulting flux of molecules passing through the cross-section of the cylindrical channel as a function of the sticking coefficient of gas molecules in the case of the diffuse-specular scattering can be characterized by a minimum.
The effect of the electric field on free-molecule gas flow in channels (pores) is also considered. It is known that adsorbed molecules often carry an electric charge (its sign and magnitude depend on both the adsorbate and the adsorbent). The electric field can affect molecules adsorbed on the channel wall that in turn leads to a change in the resulting flux of molecules passing through the channel. An approximate solution to the integro-differential equation for the concentration of gas molecules adsorbed on the inner surface of the cylindrical channel is obtained.
This work was supported in part by GACR projects 101/05/2214, 101/05/2524 and 104/07/1093.
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