Newsgroups: sci.physics.plasma
From news@news.nsw.CSIRO.AU Wed Jan 31 18:46:44 1996
From: tonym@swifty.dap.CSIRO.AU (Tony Murphy)
Organization: CSIRO, Division of Applied Physics, Sydney
Subject: Re: decreasing viscosity of high temperature (ionized) air

In article <4e5inr$fc@mojo.eng.umd.edu>, Michel Decré <decre@vki.ac.be> wrote:
>Does anybody know why the viscosity of high temperature (ionized)
>air decreases from T > T(visc-max) (from Gupta et al., NASA-RP-1260, 1991)
>-- instead of increasing as in "standard" gases ?
>

Viscosity is inversely proportional to the collision cross-sections
for interactions between the species present. At high-temperatures, these
are charged species, e.g, N+, O+, e-, etc. The collision cross-section
for the Coulomb interactions between charged species is larger than
the cross-sections for interactions between neutral species (and increases
as the level of ionisation increases). Hence, once a gas is strongly ionised,
its viscosity starts to decrease as temperature increases. This
is true for all gases, not just air.
______________________________________________________________________________
Tony Murphy (Dr), Principal Research Scientist
CSIRO Division of Applied Physics
P.O. Box 218, Lindfield NSW 2070, Australia
Phone: +61 2 413 7150 ___ Fax: +61 2 413 7204 ___ E-mail: tonym@dap.csiro.au
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