Geometry effects on rarefied nanochannel flows

A three dimensional molecular dynamics method was used to study the effect of different geometries for rarefied gas flows in nanochannels. Argon molecules have been used. The velocity profiles in the channel were obtained and analyzed with three different channel geometries: a circular, a rectangular (square), and a slit channel. A channel width of 50 nm was used for the simulation. It was found that when using the same driving force, the maximum velocity of the flow increases when the geometry changes in the order from circular to rectangular to slit geometry, where the latter becomes 2–2.5 times as large compared with either the rectangular or circular channel. For Kn larger than 1.0, the rectangular channel showed a similar maximum and slip velocity as the circular channel while the velocity profile was qualitatively similar to the slit channel. The effect of different Knudsen numbers on the velocity profiles was also investigated. We found that for Kn larger than 2–3, the Knudsen number has a relatively small influence on the slip velocity for circular channels and rectangular channels. The effect of the accommodation coefficient on the average flow velocity for all three geometries was studied and expressed as an allometric equation model