How to Specify DENSITY in MATL for Complex Pyrolysis Model (without RAMP)

[MNJOLE]

Hello,

In the FDS User Guide, it's stated that "the DENSITY of a material cannot be controlled with a RAMP function."
I'm currently setting up a simulation using the Complex Pyrolysis Model, and I'm unsure how to correctly specify the material density under these constraints.

Since temperature-dependent density cannot be defined via a RAMP, how should I handle this in the &MATL input?

• Should I enter the initial density at ambient conditions?
• Or an averaged density assuming temperature variation?
• Is there any workaround or recommended practice for materials that undergo thermal expansion or density changes with temperature?

Any insights or suggestions from those with experience modeling temperature-sensitive materials in FDS would be appreciated.

Thanks in advance.

[Vojta-Salek]

Hello, enter the material's density before thermal decomposition. In the Complex Pyrolysis Model, the density is recalculated based on the reaction kinetics, which define how density (in fact mass) changes over time as a function of temperature. This is why density cannot be specified with a RAMP function—it is a model-dependent variable.

[MNJOLE]

Thank you for your advice!

[mcgratta]

You can create a one-step reaction that converts material A to material B, where A and B have similar properties but different densities.

[MNJOLE]

I see, that was an approach I hadn’t considered! Thank you for your help!