Soot visibility
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clem...@tpi.setec.fr
May 28, 2010, 9:00:15 AM5/28/10
to FDS and Smokeview Discussions
I have e few questions concerning the soot visibility.
I am simulating fire in tunnel and we need to approximate the
visibility there is in the tunnel, to know if the users will be able
to see the emergency exit.
I am using the slice with the quantity "soot visibility"
The dimension of this quantity is meter.
The theory I read about the visibility in fire is :
The visibility is relative to what you are watching. You can see a
light at 30 meters but don't see a road sign at 5 meters. That depends
on the opacity of the smoke.
In the tunnel's norm, they use the opacity of the smoke which can be
directly linked with the visibility with a coefficient depending on
the road sign.
In FDS what are the standards you took to say that the visibility is
20meters for example. How are you claculating that ? Do you refer to
the opacity too ? And if yes, which coefficient do you use to
calculated the visibility ?
Thanks for your help !
I am simulating fire in tunnel and we need to approximate the
visibility there is in the tunnel, to know if the users will be able
to see the emergency exit.
I am using the slice with the quantity "soot visibility"
The dimension of this quantity is meter.
The theory I read about the visibility in fire is :
The visibility is relative to what you are watching. You can see a
light at 30 meters but don't see a road sign at 5 meters. That depends
on the opacity of the smoke.
In the tunnel's norm, they use the opacity of the smoke which can be
directly linked with the visibility with a coefficient depending on
the road sign.
In FDS what are the standards you took to say that the visibility is
20meters for example. How are you claculating that ? Do you refer to
the opacity too ? And if yes, which coefficient do you use to
calculated the visibility ?
Thanks for your help !
dr_jfloyd
May 28, 2010, 9:35:16 AM5/28/10
to FDS and Smokeview Discussions
S.Desanghere
May 29, 2010, 12:36:51 PM5/29/10
to FDS and Smokeview Discussions
The visibility distance is calculated by FDS by the formula:
S = C / (Km * rho * Ysoot) [in meter]
with C = 3 and Km = 8700 m²/kg by default. When there is no soot
(Ysoot=0), S should be infinity. In FDS, the maximum value for S is 30
m (arbitrary choice).
Ysoot is the local value of the mass fraction of soot (deduced from
the mixture fraction calculation: so the way you define the combustion
reaction matters ! (soot yield)).
S is the visibility distance within a homogeneous medium whose soot
concentration is Ysoot. As a consequence, this estimation is wrong for
instance if you are in a small zone without smoke which is surrounded
by smoke. In this case, you should see a kind of "smoke wall". You
have to solve the radiative transport equation to treat such a case.
Finally, I suggest you to read the following reference :
http://fire.nist.gov/bfrlpubs/fire02/PDF/f02072.pdf
Cheers
Sylvain
On 28 mai, 15:00, "clemen...@tpi.setec.fr" <clemen...@tpi.setec.fr>
wrote:
S = C / (Km * rho * Ysoot) [in meter]
with C = 3 and Km = 8700 m²/kg by default. When there is no soot
(Ysoot=0), S should be infinity. In FDS, the maximum value for S is 30
m (arbitrary choice).
Ysoot is the local value of the mass fraction of soot (deduced from
the mixture fraction calculation: so the way you define the combustion
reaction matters ! (soot yield)).
S is the visibility distance within a homogeneous medium whose soot
concentration is Ysoot. As a consequence, this estimation is wrong for
instance if you are in a small zone without smoke which is surrounded
by smoke. In this case, you should see a kind of "smoke wall". You
have to solve the radiative transport equation to treat such a case.
Finally, I suggest you to read the following reference :
http://fire.nist.gov/bfrlpubs/fire02/PDF/f02072.pdf
Cheers
Sylvain
On 28 mai, 15:00, "clemen...@tpi.setec.fr" <clemen...@tpi.setec.fr>
wrote:
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