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Old   April 17, 2002, 13:25
Default Smoke visibility
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André
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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.
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Old   April 18, 2002, 09:34
Default Re: Smoke visibility
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walter schwarz
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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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Old   December 5, 2020, 07:01
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Mahesh
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Quote:
Originally Posted by walter schwarz
;100584
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
But wherever the smoke concentration is Zero, the value is becoming zero and the results are not being plotted. Please suggest how to overcome this.
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Old   December 5, 2020, 10:21
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Quote:
Originally Posted by mahesh1819 View Post
But wherever the smoke concentration is Zero, the value is becoming zero and the results are not being plotted. Please suggest how to overcome this.
The value of what is becoming zero?
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Old   December 5, 2020, 11:01
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Originally Posted by pakk View Post
The value of what is becoming zero?
Sry for my mistake. I meant to say that the visibility is becoming infinite where the smoke concentration is zero and I could not plot the visibility as the post processing shows error. Kindly help me how to plot in such case.

Thanks in advance
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Old   December 5, 2020, 15:05
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Make it finite but a big value in such case. I have no idea how you implemented this, because you did not give any info, so I can't tell you how to change your implementation.
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