Volume 59, Number 6, September II 2002
|Page(s)||800 - 806|
|Published online||01 September 2002|
Tracer diffusivity in a time- or space-dependent temperature field
Institute for Advanced Studies in Basic Sciences
- Zanjan, 45195-159, Iran
2 Laboratoire de Physico-Chimie Théorique, UMR CNRS 7083, ESPCI 75231 Paris Cedex 05, France
3 Institute for Studies in Theoretical Physics and Mathematics P.O. Box 19395-5531, Tehran, Iran
Accepted: 20 June 2002
The conventional assumption that the self-diffusion coefficient of a small tracer can be obtained by a local and instantaneous application of Einstein's relation in a temperature field with spatial and temporal heterogeneity is revisited. It is shown that hydrodynamic fluctuations contribute to the self-diffusion tensor in a universal way, i.e. independent of the size and shape of the tracer. The hydrodynamic contribution is anisotropic —it reflects knowledge of the global anisotropy in the temperature profile, leading to an anisotropic self-diffusion tensor for a spherical tracer. It is also retarded —it creates memory effects during the diffusion process due to hydrodynamic interactions.
PACS: 05.40.-a – Fluctuation phenomena, random processes, noise, and Brownian motion / 66.10.Cb – Diffusion and thermal diffusion / 05.60.Cd – Classical transport
© EDP Sciences, 2002
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