I have an issue with Pyrosim: I can't propagate a fire from a single source to the near objects.
I've modeled the fire source with fixed HRR and a fixed Temp., while the sorrounding objects as "Layered Surfaces" (1 Material) with "Ignition Temperature".
I've followed the indications given by your tutorial: https://support.thunderheadeng.com/tutorials/pyrosim/modeling-fire/.
I notice that the Temperature of the closest object doesn't change from 20 degree. This is impossible from a thermodynamic point of view !
Shall you give me an help ?
Due to the higher thermal conductivity of the material that you are specifying for the surface, heat is being lost from the surface into the solid very quickly. The surface temperature is increasing over time, but very slowly, as the heat is conducted away quickly.
It seems that the properties are closer to a metal than a combustible solid that warms up at the surface and begins to decompose into pyrolyzate. As a test, if you swap your material in the surface to something like FOAM or PINE from the materials library, you will see the surface heat up quickly and ignite. Note: you will have to remove the reactions from the materials since you are defining it in the surface properties.
There are many ways to release fuel gas from surfaces for gas phase combustion, you can see the details in the FDS User Guide section '11.4 Simple Pyrolysis Models' where the different options are presented. The section after that goes into more complex options where FDS models the 'physics' of the solid phase reaction to produce fuel gas.
You are specifying the reaction in the surface, but you could let it be governed by the solid phase reaction in the material properties. The way you did it provides more control over the HRR from the surface. The downside of that approach, is that the energy feedback to the surface is not used to drive the pyrolysis reaction in the solid. You would need to specify more parameters in the solid reaction that would require a sensitivity study on them as well, and more work to justify them.
So many options, so little time. :D
Bryan Klein posted about 1 month ago Admin Answer
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