Transport coefficients of hard sphere fluids
UNSPECIFIED. (2003) Transport coefficients of hard sphere fluids. MOLECULAR PHYSICS, 101 (3). pp. 469-482. ISSN 0026-8976Full text not available from this repository.
Official URL: http://dx.doi.org/10.1080/0026897021000037717
New calculations have been made of the self-diffusion coefficient D, the shear viscosity eta(s), the bulk viscosity eta(b) and thermal conductivity lambda of the hard sphere fluid, using molecular dynamics (MD) computer simulation. A newly developed hard sphere MD scheme was used to model the hard sphere fluid over a wide range up to the glass transition (similar to0.57 packing fraction). System sizes of up to 32 000 hard spheres were considered. This set of transport coefficient data was combined with others taken from the literature to test a number of previously proposed analytical formulae for these quantities together with some new ones given here. Only the self-diffusion coefficient showed any substantial N dependence for N>500 at equilibrium fluid densities (xi<0.494). D increased with N, especially at intermediate densities in the range ξ&SIM;0.3-0.35. The expression for the packing fraction dependence of D proposed by Speedy, R.J., 1987, Molec. Phys., 62, 509 was shown to fit these data well for N&SIM;500 particle systems. We found that the packing fraction ξ dependence of the two viscosities and thermal conductivity, generically denoted by X, were represented well by the simple formula X/X-0=1/[1-(ξ/ξ(1))](m) within the equilibrium fluid range 0<xi<0.493. This formula has two disposable parameters,ξ(1) and m, and X-0 is the value of the property X in the limit of zero density. This expression has the same form as the Krieger-Dougherty formula (Kreiger, I. M., 1972, Adv. Colloid. Interface Sci., 3, 111) which is used widely in the colloid literature to represent the packing fraction dependence of the Newtonian shear viscosity of monodisperse colloidal near-hard spheres. Of course, in the present case, X-0 was the dilute gas transport coefficient of the pure liquid rather than the solvent viscosity. It was not possible to fit the transport coefficient normalized by their Enskog values with such a simple expression because these ratios are typically of order unity until quite high packing fractions and then diverge rapidly at higher values over a relatively narrow density range. At the maximum equilibrium fluid packing fraction ξ=0.494 for both the hard sphere fluid and the corresponding colloidal case a very similar value was found for η(s)/η(0)&SIM;30-40, suggesting that the 'crowding' effects and their consequences for the dynamics in this region of the phase diagram in the two types of liquid have much in common. For the hard sphere by MD, D-0/D&SIM;11 at the same packing fraction, possibly indicating the contribution from 'hydrodynamic enhancement' of this transport coefficient, which is largely absent for the shear viscosity. Interestingly the comparable ratio for hard sphere colloids is the same.
|Item Type:||Journal Article|
|Subjects:||Q Science > QC Physics|
|Journal or Publication Title:||MOLECULAR PHYSICS|
|Publisher:||TAYLOR & FRANCIS LTD|
|Official Date:||10 February 2003|
|Number of Pages:||14|
|Page Range:||pp. 469-482|
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