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Title: Molecular-Level Simulations of Gas Dynamic Flows.


Abstract not provided.

Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Resource Type:
Resource Relation:
Conference: Proposed for presentation at the University of Colorado at Colorado Springs Colloqium held April 2-3, 2015 in Colorado Springs, Colorado.
Country of Publication:
United States

Citation Formats

Gallis, Michail A. Molecular-Level Simulations of Gas Dynamic Flows.. United States: N. p., 2015. Web.
Gallis, Michail A. Molecular-Level Simulations of Gas Dynamic Flows.. United States.
Gallis, Michail A. Wed . "Molecular-Level Simulations of Gas Dynamic Flows.". United States. doi:.
title = {Molecular-Level Simulations of Gas Dynamic Flows.},
author = {Gallis, Michail A.},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Apr 01 00:00:00 EDT 2015},
month = {Wed Apr 01 00:00:00 EDT 2015}

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  • Abstract not provided.
  • The purpose of this project was to develop methods and tools that will aid in safety evaluation of nuclear fuels and licensing of nuclear reactors relating to accidents.The objectives were to develop more detailed and faster computations of fission product transport and aerosol evolution as they generally relate to nuclear fuel and/or nuclear reactor accidents. The two tasks in the project related to molecular transport in nuclear fuel and aerosol transport in reactor vessel and containment. For both the tasks, explorations of coupling of Direct Simulation Monte Carlo with Navier-Stokes solvers or the Sectional method were not successful. However, Meshmore » free methods for the Direct Simulation Monte Carlo method were successfully explored.These explorations permit applications to porous and fractured media, and arbitrary geometries.The computations were carried out in Mathematica and are fully parallelized. The project has resulted in new computational tools (algorithms and programs) that will improve the fidelity of computations to actual physics, chemistry and transport of fission products in the nuclear fuel and aerosol in reactor primary and secondary containments.« less
  • Improved power density and freeze-thaw durability in automotive applications of Proton Exchange Membrane Fuel Cells (PEMFCs) requires effective water management at the membrane. This is controlled by a porous hydrophobic gas-diffusion-layer (GDL) inserted between the membrane catalyst layer and the gas reactant channels. The GDL distributes the incoming gaseous reactants on the catalyst surface and removes excess water by capillary action. There is, however, limited understanding of the multiphase, multi-component transport of liquid water, vapor and gaseous reactants within these porous materials. This is due primarily to the challenges of in-situ diagnostics for such thin (200 -“ 300 {microns}), opticallymore » opaque (graphite) materials. Transport is typically analyzed by fitting Darcy's Law type expressions for permeability, in conjunction with capillary pressure relations based on formulations derived for media such as soils. Therefore, there is significant interest in developing predictive models for transport in GDLs and related porous media. Such models could be applied to analyze and optimize systems based on the interactions between cell design, materials, and operating conditions, and could also be applied to evaluating material design concepts. Recently, the Lattice Boltzmann Method (LBM) has emerged as an effective tool in modeling multiphase flows in general, and flows through porous media in particular. This method is based on the solution of a discrete form of the well-known Boltzmann Transport Equation (BTE) for molecular distribution, tailored to recover the continuum Navier-Stokes flow. The kinetic theory basis of the method allows simple implementation of molecular forces responsible for liquid-gas phase separation and capillary effects. The solution advances by a streaming and collision type algorithm that makes it suitable to implement for domains with complex boundaries. We have developed both single and multiphase LB models and applied them to simulate flow through porous GDL materials. We will present an overview of the methods as implemented, verification studies for both microstructure reconstruction and transport simulations, and application to single- and two-phase transport in GDL structures. The applications studies are designed to both improve understanding of transport within a given structure, and to investigate possible routes for improving material properties through microstructure design.« less
  • Abstract not provided.
  • In this paper, we report recent lattice gas simulations for single-phase and two-phase flows for two dimensional problems using the Connection Machine-2. For the single-phase fluid problem, we use the standard 7-bit lattice gas model with the maximum collision rules. The velocity and vorticity field of the Kelvin-Helmholtz instability is studied. It is shown that the lattice gas method preserves the main properties of the flow patterns observed in other numerical simulations. Using colored particles and holes, the lattice gas method is extended to simulate immiscible fluids with adjustable surface tension, using a purely local collision scheme. The locality ofmore » this model allows us to implement a very fast and parallel algorithm on the Connection Machine-2. Because this new model correctly describes short-range particle-particle interactions between liquids and also particle-solid interactions between the fluid and the wall, cohesion and wettability can be simulated. Applications of the current model to several physical systems including spinodal decomposition, Rayleigh-Taylor flows and wettability in two-phase flows through porous media are discussed. 15 refs., 10 figs.« less