Coupling atomistic and continuum models for multi-scale simulations of gas flows

This paper describes two computational tools linking atomistic and continuum models of gaseous systems. The first one, a Unified Flow Solver (UFS), is based on a direct Boltzmann solver and kinetic CFD schemes. The UFS uses an adaptive mesh and algorithm refinement procedure for automatic decomposition of computational domain into kinetic and continuum parts. The UFS has been used for a variety of flow problems in a wide range of Knudsen and Mach numbers. The second tool is a Multi-Scale Computational Environment (MSCE) integrating CFD tools with Kinetic Monte Carlo (KMC) and Molecular Dynamics (MD). The MSCE was applied for analysis of catalytic growth of vertically aligned carbon nanotubes (CNT) in a C2H2/H-2 inductively coupled plasma. The MSCE is capable of predicting paths for delivering carbon onto catalyst/CNT interface, formation of single wall or multi-wall CNTs depending on the shape of catalyst, and transition from nucleation to the steady growth of CNTs.