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Old   February 28, 2013, 08:53
Default burning surface
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I’d like to simulate a room fire with CFX. So that my combustible surface starts to burn, I decided to create a wall boundary with a source condition that has a mass flow of combustible gas. My mass flow begins when the wall boundary has a specific average temperature. For that, I use a known CEL function “areaAve(T)@...” .
Everything works. I have a combustion – so far so good.

But, if you have large surfaces, like a carpet, it isn’t realistic that the whole surface starts to outlet a combustible gas overall.

Therefore, my idea was to create a mass flow expression for every mesh cell on my boundary. That means, if one cell has a specific temperature the area-related mass flow starts for this cell. Unfortunately I found no kind of CEL function that allow me to access a mesh cell of my boundary and nothing in the documentation that help me to realize my idea.

Maybe you have a kind of idea to solve my problem. Thanks at all.
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Old   February 28, 2013, 17:42
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In CEL you do not have access to cell information, you just write the equation as a continuum and let CFX take care of it.

So a simple function like if(T>threshold,source_term=something,source_term=0 ) should do the trick.
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Old   March 1, 2013, 09:05
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Thanks for response.
An IF – function was also an idea of mine. But it still the same problem, because I have also a fixed value for the source term (e.g. kg/s) above my whole boundary (wall).

What I need is a function or a command that says my boundary when you’ve got a specific temperature in one cell or at a special point on this boundary, you have to start with the outflow only in this point/cell . And when another region of the boundary reaches this temperature it has to begin with the same outflow.

Maybe CFX has no solution for this kind of special simulation.
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Old   March 3, 2013, 06:15
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I do not see your point. I cannot see why you think the simple equation I quoted will not work. Can you explain it again?
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Old   March 4, 2013, 05:52
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My bad. Sorry.
I tried some other simulations with a bigger surface, so I had a better temperature profile on my surface. The result was a mass outflow of every surface mesh cell which reaches the specific temperature. So your if-function was the right way and I thank you very much for your help.
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