Differential diffusion: Often a finite-mising length effect

Nielsen, Peter and Teakle, Ian A.L. (2004). Differential diffusion: Often a finite-mising length effect. In: M. Behnia, W. Lin and G. d McBain, 15th Australasian Fluid Mechanics Conference. 15th Australasian Fluid Mechanics Conference, Sydney, NSW, Australia, (1-4). 13-17 December 2004.

Author Nielsen, Peter
Teakle, Ian A.L.
Title of paper Differential diffusion: Often a finite-mising length effect
Conference name 15th Australasian Fluid Mechanics Conference
Conference location Sydney, NSW, Australia
Conference dates 13-17 December 2004
Proceedings title 15th Australasian Fluid Mechanics Conference
Place of Publication Sydney, NSW, Australia
Publisher University of Sydney
Publication Year 2004
Sub-type Fully published paper
ISBN 1864876956
Editor M. Behnia
W. Lin
G. d McBain
Volume CD Rom
Start page 1
End page 4
Total pages 4
Collection year 2004
Language eng
Abstract/Summary Many instances of differential diffusion, i e, different species having different turbulent diffusion coefficients in the same flow, can be explained as a finite mixing length effect. That is, in a simple mixing length scenario, the turbulent diffusion coefficient has the form 1 ( m )2 m m c l K w l OL   =  +    where, wm is the mixing velocity, lm the mixing length and Lc the overall distribution scale for a particular species. The first term represents the familiar gradient diffusion while the second term becomes important when lm/Lc is finite. This second term shows that different species will have different diffusion coefficients if they have different overall distribution scales. Such different Lcs may come about due to different boundary conditions and different intrinsic properties (molecular diffusivity, settling velocity etc) for different species. For momentum transfer in turbulent oscillatory boundary layers the second term is imaginary and explains observed phase leads of shear stresses ahead of velocity gradients.
Subjects 290802 Water and Sanitary Engineering
770402 Land and water management
Q-Index Code E1
Q-Index Status Provisional Code
Institutional Status UQ

 
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Created: Thu, 23 Aug 2007, 20:11:12 EST