Smoluchowski thermostat: a numerical demonstration of the tangential momentum accommodation coefficient

In this research, numerical simulations are used to study the flow of a monoatomic rarefied gas inside a model cylinder with a nanopore diameter. In the rarefied gas regime, gas-gas collisions seldom occur and molecular transport can be fully attributed to gas-wall collisions. The most important parameter in describing the gas-surface interaction is the tangential momentum accommodation coefficient (TMAC). This parameter represents the fraction of gas-wall collisions that are reflected diffusely. Present work shows that the Smoluchowski thermostat, a simulation technique that mimics a diffusive gas-wall collision satisfies Maxwell's boundary condition by calculating this coefficient numerically. The method involves placing an ideal gas in a weak constant gravitational field. The TMAC is determined by computing the correlation between the impinging and outgoing drift velocities at the cylinder surface. While most simulation studies compare their computed TMAC's with other relevant studies, the method discussed here enables one to compare the computed TMAC with an input parameter.