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Thermophoresis of particles in a heated boundary layer

Published online by Cambridge University Press:  19 April 2006

L. Talbot
Affiliation:
Mechanical Engineering Department and Lawrence Berkeley Laboratory, University of California
R. K. Cheng
Affiliation:
Lawrence Berkeley Laboratory
R. W. Schefer
Affiliation:
Lawrence Berkeley Laboratory
D. R. Willis
Affiliation:
Mechanical Engineering Department, University of California

Abstract

A laser-Doppler velocimeter (LDV) study of velocity profiles in the laminar boundary layer adjacent to a heated flat plate revealed that the seed particles used for the LDV measurements were driven away from the plate surface by thermophoretic forces, causing a particle-free region within the boundary layer of approximately one half the boundary-layer thickness. Measurements of the thickness of this region were compared with particle trajectories calculated according to several theories for the thermophoretic force. It was found that the theory of Brock, with an improved value for the thermal slip coefficient, gave the best agreement with experiment for low Knudsen numbers, λ/R = O(10−1), where λ is the mean free path and R the particle radius.

Data obtained by other experimenters over a wider range of Knudsen numbers are compared, and a fitting formula for the thermophoretic force useful over the entire range 0 [les ] λ/R [les ] ∞ is proposed which agrees within 20% or less with the majority of the available data.

Type
Research Article
Copyright
© 1980 Cambridge University Press

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