Molecular flows in narrow pores at small initial perturbations

Abstract

The problem of the correctness of setting the initial conditions upon the generation of a molecular flow in narrow pores is discussed. The effect of intensity of the initial perturbation of the equilibrium state of the vapor and liquid in a 15-nm-wide slitlike pore with different potential of interaction between the molecules and pore walls is studied. The microhydrodynamic approach is used to calculate the flows of dense gas and liquid in narrow pores, which makes it possible to investigate the effect of wall potential on the parameters of molecular flows. The calculations are made on the basis of the Navier-Stokes type equations in which the transport coefficients and the equation of state for a component are calculated using a simple molecular model such as the lattice-gas model. The transport coefficients and the equation of state depend on the local values of the vapor and liquid densities and on temperature. The dynamic pattern of vapor flow is shown to qualitatively remain the same at a decreasing intensity of the initial unimoment perturbation: it is of oscillating nature, just as at strong initial perturbations. Weak attraction of the molecules to the walls enhances oscillations at the initial stage of gas and liquid flow along the pore axis. Strong attraction between low-density molecules and the pore walls forms a laminar flow, and the oscillations are noticeably smoothed. The perturbation intensity changes the absolute values of the flow parameters, including the average rates of the molecular flows formed. The average rate of hydrodynamic flow in wide pores depends weakly on the energy of interaction between the molecules and the pore walls.