Absorption coefficient for black PMMA

[Morgan Bruns]

There was a good deal of discussion yesterday about absorption coefficients. As we said, one of the reasons why black PMMA was chosen was so that we would limit the relative importance of in-depth radiation. However, we do not know for certain how important the absorption coefficient is for the specific black PMMA that we have been studying. So it would probably be valuable if someone dug into this a little bit more---especially to get some idea of what the spectral dependence of the absorption coefficient is.

Several references were suggested by participants. I didn't write them all down, but these are the ones that I can remember:

(1) Linteris et al. (2011), https://doi.org/10.1002/fam.1113

(2) Bal and Rein (2011), https://doi.org/10.1016/j.combustflame.2010.10.014

Please list other relevant references if you know of any.

[Stanislav I. Stoliarov]

I think that for the experiments involving radiators that are at a modest temperature (1000 - 1500 K),  the choice of exact value of this absorption coefficient is not critical. In our modeling effort  (https://doi.org/10.1016/j.firesaf.2020.103083), we chose to use the Linteris' data on a similar black PMMA, which yielded the value of 2870 m-1.  Changing this value up or down by 30% produces very little change in the pyrolysis model predictions.  For radiators at high temperature (such as used in an FPA), this absorption coefficient can be significantly (as much as a factor of 2) lower.  When this coefficient so low, the sensitivity of the pyrolysis modeling results to its value becomes significant.

  

Stas