Enhancement of diffusive transport by non-equilibrium thermal fluctuations

Aleksandar Donev, John B. Bell, Anton De La Fuente, Alejandro L. Garcia

Research output: Contribution to journalArticlepeer-review

Abstract

We study the contribution of advection by thermal velocity fluctuations to the effective diffusion coefficient in a mixture of two identical fluids. The steady-state diffusive flux in a finite system subject to a concentration gradient is enhanced because of long-range correlations between concentration fluctuations and fluctuations of the velocity parallel to the concentration gradient. The enhancement of the diffusive transport depends on the system size L and grows as ln(L/L0) in quasi-two-dimensional systems, while in three dimensions it grows as L0- 1 - L- 1, where L0 is a reference length. The predictions of a simple fluctuating hydrodynamics theory, closely related to second-order mode-mode coupling analysis, are compared to results from particle simulations and a finite-volume solver and excellent agreement is observed. We elucidate the direct connection to the long-time tail of the velocity autocorrelation function in finite systems, as well as finite-size corrections employed in molecular dynamics calculations. Our results conclusively demonstrate that the nonlinear advective terms need to be retained in the equations of fluctuating hydrodynamics when modeling transport in small-scale finite systems.

Original languageEnglish (US)
Article numberP06014
JournalJournal of Statistical Mechanics: Theory and Experiment
Volume2011
Issue number6
DOIs
StatePublished - Jun 2011

Keywords

  • diffusion
  • hydrodynamic fluctuations
  • molecular dynamics
  • rarefied gas dynamics

ASJC Scopus subject areas

  • Statistical and Nonlinear Physics
  • Statistics and Probability
  • Statistics, Probability and Uncertainty

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