Criteria for local equilibrium in a system with transport of heat and mass
 Bjørn Hafskjold,
 Signe Kjelstrup Ratkje
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Nonequilibrium molecular dynamics is used to compute the coupled heat and mass transport in a binary isotope mixture of particles interacting with a LennardJones/spline potential. Two different stationary states are studied, one with a fixed internal energy flux and zero mass flux, and the other with a fixed diffusive mass flux and zero temperature gradient. Computations are made for one overall temperature,T=2, and three overall number densities,n=0.1, 0.2, and 0.4. (All numerical values are given in reduced, LennardJones units unless otherwise stated.) Temperature gradients are up to ∇T=0.09 and weightfraction gradients up to ∇w _{1}=0.007. The fluxforce relationships are found to be linear over the entire range. All four transport coefficients (theLmatrix) are determined and the Onsager reciprocal relationship for the offdiagonal coefficients is verified. Four different criteria are used to analyze the concept of local equilibrium in the nonequilibrium system. The local temperature fluctuation is found to be δT≈0.03T and of the same order as the maximum temperature difference across the control volume, except near the cold boundary. A comparison of the local potential energy, enthalpy, and pressure with the corresponding equilibrium values at the same temperature, density, and composition also verifies that local equilibrium is established, except near the boundaries of the system. The velocity contribution to the BoltzmannHfunction agrees with its Maxwellian (equilibrium) value within 1%, except near the boundaries, where the deviation is up to 4%. Our results do not support the Eyringtype transport theory involving jumps across energy barriers; we find that its estimates for the heat and mass fluxes are wrong by at least one order of magnitude.
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 Title
 Criteria for local equilibrium in a system with transport of heat and mass
 Journal

Journal of Statistical Physics
Volume 78, Issue 12 , pp 463494
 Cover Date
 19950101
 DOI
 10.1007/BF02183360
 Print ISSN
 00224715
 Online ISSN
 15729613
 Publisher
 Kluwer Academic PublishersPlenum Publishers
 Additional Links
 Topics
 Keywords

 Nonequilibrium molecular dynamics
 irreversible thermodynamics
 Onsager reciprocal relations
 local equilibrium
 Industry Sectors
 Authors

 Bjørn Hafskjold ^{(1)}
 Signe Kjelstrup Ratkje ^{(1)}
 Author Affiliations

 1. Department of Physical Chemistry, University of Trondheim, Norwegian Institute of Technology, N7034, Trondheim, Norway