On the role of the Knudsen layer in rapid granular flows
- Univ. of Colorado, Boulder, CO
- Loughborough Univ., Loughborough, Leicestershire, UK
A combination of molecular dynamics simulations, theoretical predictions and previous experiments are used in a two-part study to determine the role of the Knudsen layer in rapid granular flows. First, a robust criterion for the identification of the thickness of the Knudsen layer is established: a rapid deterioration in Navier–Stokes order prediction of the heat flux is found to occur in the Knudsen layer. For (experimental) systems in which heat flux measurements are not easily obtained, a rule-of-thumb for estimating the Knudsen layer thickness follows, namely that such effects are evident within 2.5 (local) mean free paths of a given boundary. Secondly, comparisons of simulation and experimental data with Navier–Stokes order theory are used to provide a measure as to when Knudsen-layer effects become non-negligible. Specifically, predictions that do not account for the presence of a Knudsen layer appear reliable for Knudsen layers collectively composing up to 20% of the domain, whereas deterioration of such predictions becomes apparent when the domain is fully comprised of the Knudsen layer.
- Research Organization:
- University of Colorado, Boulder, CO; Loughborough University, Loughborough, Leicestershire, UK; National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR
- Sponsoring Organization:
- Engineering and Physical Sciences Research Council; National Science Foundation; University of Colorado, Boulder, CO; Loughborough University, Loughborough, Leicestershire, UK; USDOE - Office of Fossil Energy (FE)
- OSTI ID:
- 937566
- Report Number(s):
- DOE/NETL-IR-2007-261; NETL-TPR-1784; EP/D030676/1; GR/R75694/01); NSF PHY99-07949; NSF CTS-0318999
- Journal Information:
- Journal of Fluid Mechanics, Journal Name: Journal of Fluid Mechanics Vol. 585; ISSN 0022-1120; ISSN 1469-7645
- Publisher:
- Cambridge University Press
- Country of Publication:
- United States
- Language:
- English
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