Density or soot density, evaluate smoke opacity

[Rosanna Caporusso]

Hello everybody,

I need your help: I ​​need to assess the visibility of emergency signs inside a building.

To do this I need to evaluate the smoke density and opacity.

Can you tell me the difference between DENSITY and SOOT DENSITY in pyrosim 3DPLOT?

Also, do you have any ideas on how I can evaluate smoke density and opacity?

I hope to get your help,  

Thank you for your attention

[Randy McDermott]

DENSITY is the mass per unit volume of the local fluid mixture.

SOOT DENSITY is Y_SOOT * DENSITY, where Y_SOOT is the local mass fraction of soot.

I would study the "beam detector" case from the user guide.

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[Ali Khalid]

Hi Rosanna,

I believe if you are interested in evaluating the visibility criteria for egress modeling, better to use the Pyrosim "Visibility output" with 2D or 3D slice. In addition to that, measure the smoke layer height measuring device at different points of interest.

Regards,

Ali

On Wed, Oct 21, 2020 at 9:48 AM Rosanna Caporusso <rosann...@gmail.com> wrote:

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[dr_jfloyd]

When you have a SLCF of the FDS output quantity of VISIBILITY what you get is the visibility computed in each grid cell in the slice. This does not always directly tell you if you can see a particular object form a particular view point. Obviously, if the VISIBILITY everywhere between the object and the viewing location is greater than the distance, then you know you can see the object. Similarly, if the VISIBILITY everywhere between the object and the viewing location is less than the distance, then you know you will not see the object see the object. If you have a mix where some regions are greater than the distance and some are less, then you need to do an integration over the path length.

On Wednesday, October 21, 2020 at 10:08:10 AM UTC-4, Ali Khalid wrote:

Hi Rosanna,

I believe if you are interested in evaluating the visibility criteria for egress modeling, better to use the Pyrosim "Visibility output" with 2D or 3D slice. In addition to that, measure the smoke layer height measuring device at different points of interest.

Regards,

Ali

On Wed, Oct 21, 2020 at 9:48 AM Rosanna Caporusso <rosann...@gmail.com> wrote:

Hello everybody,

I need your help: I ​​need to assess the visibility of emergency signs inside a building.

To do this I need to evaluate the smoke density and opacity.

Can you tell me the difference between DENSITY and SOOT DENSITY in pyrosim 3DPLOT?

Also, do you have any ideas on how I can evaluate smoke density and opacity?

I hope to get your help,  

Thank you for your attention

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[Rosanna Caporusso]

Thank you all for the answer. 

I have another question: what do you think the opacity of smoke depends on?  

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[Kevin McGrattan]

First, the mass per unit volume of particulate matter.  Second, the optical properties of the particulate, like size, scattering radius, etc.

[Rosanna Caporusso]

I had been thinking about soot density. Is it possible to evaluate the optical properties in some way?  

[Kevin McGrattan]

SFPE Handbook, Chapter 24, Smoke Characterization and Damage Potentials
Jeffrey S. Newman, Geary G. Yee, and Paul Su

This could be a good place to start learning about soot and smoke.

[Rosanna Caporusso]

Hello everyone, I have a new problem. 

I understood that DENSITY is the mass per unit volume of the local fluid mixture. 

SOOT DENSITY is Y_SOOT * DENSITY, where Y_SOOT is the local mass fraction of soot. 

But I don't understand one thing. 

I have a soot yield Ysoot = 0.07075. 

At instant t = 100 s, I have a soot density equal to 0.0000653 Kg / m3. 

Therefore: DENSITY = SOOT DENISTY / Ysoot = 0.0000653 / 0.07075 = 0.000922 Kg / m3. 

Why does Pyrosim show me a DENSITY equal to 1.133 Kg / m3? 

(I attach photos) 

Sorry for the maybe stupid question, but these are my first approaches. 

I hope you can help me, 

Thank you  

[Randy McDermott]

The soot yield you specify and the local mass fraction of soot (what I was calling Y_SOOT) are not the same thing.  I apologize if that was confusing.

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[dr_jfloyd]

Yield is the mass of a species produced (or consumed if the yield is negative) per mass of fuel burned. It has units of kg/kg and not kg/m3,

[Rosanna Caporusso]

Thanks a lot to everyone, now I understand.