Direct simulation Monte Carlo method for molecular and transitional flow regimes in vacuum components with static and moving surfaces

Abstract

The gas flow through a vacuum component can be continuous, transitional, or molecular depending on the pressure range and geometries involved. Dilute gas flows in molecular and transitional regimes were simulated using the direct simulation Monte Carlo method. The computational model takes as data combination of pressure, temperature of gas, type of gas, and geometry of the vacuum components. The results of the computations are gasflow, local velocities, and molecular density distribution. The model was first tested and validated for several simple geometries, such as circular and rectangular finite length tubes with static and moving walls, for different flow conditions. The Couette flow problem is treated in all the transition regime, from the molecular regime to the beginning of the viscous regime. The model was found to agree well with other published results, and allowed us to better understand flow phenomena for the different regimes from the molecular case to the viscous case. This first study was conducted to develop, in the future, a model that we can adapt to more complicated geometries of vacuum components, such as stages of turbomolecular or molecular pumps, to predict the flow rate from molecular to transition flow regimes.

Navier–Stokes modeling of a Gaede pump stage in the viscous and transitional flow regimes using slip-flow boundary conditions

“…In the framework of the NS formulation with slip boundary conditions, we can conclude that one-dimensional Couette flow throughput does not change in the viscous-tomolecular transition, while the shear stress is remarkably affected by the Knudsen number in the transitional regime. Boulon et al, 16 carried out a DSMC ͑direct simulation Monte Carlo͒ simulation of Couette flow between two parallel plates, in transition flow regime, for 10 −2 Ͻ KnϽ 10 2 . They showed a linear velocity profile with the slip at the walls, matching the present 1D analysis, in molecular flow regime.…”

A distributed pumping model for a repetitive operated magnetically insulated transmission line oscillator

“…This method is useful for the simulation of time dependent pressure distribution in a vacuum system with complicated chamber structures and hard to get accurate conductance. 21,22 By recording the locations of the test particles at various values of time, the time development of pressure distribution in the MILO tube from the beginning of gas desorption can be calculated. Thus, based on the MC method, a "distributed pumping" idea for a rep-rate MILO is proposed in this paper.…”