On the anisotropy of gas transfer processes in nano- and microchannels

The method of stochastic molecular modeling, developed by the authors for calculating the transport coefficients of rarefied gas in a free medium, is generalized to describe transport processes in confined conditions. The phase trajectories of the studied molecular system are simulated stochastically, and the simulation of the dynamics of the molecule is split into processes. First, its shift in the configuration space is realized, and then a possible collision with other molecules is played out. The calculation of all observables, in particular, the transport coefficients is carried out by averaging over an ensemble of independent phase trajectories. The interaction of gas molecules with the boundary is described by mirror or mirror-diffuse laws. The efficiency of the algorithm is demonstrated by calculating the selfdiffusion coefficient of argon in the nanochannel. The accuracy of modeling is investigated, its dependence on the number of particles and phase trajectories used for averaging. The viscosity of rarefied gases in the nanochannel has been systematically studied. It is shown that it is non-isotropic, and its difference along and across the channel is determined by the interaction of gas molecules with the channel walls. By changing the material of the walls, it is possible to significantly change the viscosity of the gas, and it can be several times greater than in volume, or less. The indicated anisotropy of viscosity is recorded not only in nano-, but also in microchannels.