Kinetic phenomena in the gas mixture flow through nanodimensional capillaries: The effect of surface forces

Abstract

The flow of a gaseous mixture in ultrafine capillaries whose size is comparable to the range of surface forces is studied with allowance for the effect of surface forces on gas component transport in the capillaries. The effect of surface forces is shown to be twofold. On the one hand, it is necessary to take into account the Boltzmann distribution of the molecular density in the capillary: it turns out that the contribution of this effect to the transport coefficient values may amount to 20%. On the other hand, an additional kinetic contribution to these coefficients may arise if the temperature in the gas is nonuniform. In this case, the temperature gradient may change the gas component transport coefficients several times, giving rise to a new mechanism of gas component separation that is associated with different potentials of interaction between the gas components and capillary walls. Also, surface forces modify the structure of phenomenological equations for gas component transport that implies entropy production in an inhomogeneous gas. However, the Onsager symmetry between cross coefficients is retained.