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-   -   Smoke visibility (http://www.cfd-online.com/Forums/fluent/29652-smoke-visibility.html)

André April 17, 2002 12:25

Smoke visibility
 
Dear Fluent users,

Has anyone got experience in modelling a smokesource in Fluent and setting up a value for visibility. We are allso interested in the relation between smokeproduction and heat output.

Thanks in advance.

walter schwarz April 18, 2002 08:34

Re: Smoke visibility
 
stricly speaking, smoke is a combination of carbon particulates (1-20 micron dia) and gases ... i usually model smoke as the products of the chemical equation describing the combustion and so i usually model a mixture of air and "smoke" with an air mass sink to account for oxygen consumption and a smoke mass source plus the energy source.

to report, in the way of post-processing, for the visibility in the domain of interest...

visibility post-processing is related to the mass concentration of the smoke and several fluent customers do this regularly ... here is some background information on smoke production and visibility:

http://fire.nist.gov/bfrlpubs/fire95/PDF/f95126.pdf

http://fire.nist.gov/bfrlpubs/fire00/PDF/f00164.pdf

basically visibility can be defined as the distance at which the contrast of an object relative to its backgrounds drops below a certain fraction. the visibility S, [m] depends on the smoke mass concentration C, [g/m3] and on the specific extinction coefficient Km, [m2/g] which depends on the material being burned

for a light emitting sign S = 8 / (Km*C)

for a light reflecting sign S = 3 / (Km*C)

this is simple to create a post-processing variable in fluent because the smoke concentration density is readily available


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