Monochromatic Radiation

[ETIENNE CHOPARD]

Hello everyone,

I am attempting to study monochromatic radiation from a flame. Does anyone know how I can achieve this?

I have some ideas that involve changing the absorption coefficient value of the background gas (usually air) directly in the source code (the RadCal file) to make it absorbent to all wavelengths except for a narrow zone (approximately 0.1 microns or the width of the 'pseudo-monochromatic' zone) where it would remain transparent. Has anyone tried this before or does anyone have an alternative solution?

Thank you very much!

[dr_jfloyd]

I don't think that approach will work. That approach will mean the radiant fraction of your fire will be essentially zero as all radiation emitted would just be absorbed right away and becoming an energy source term.  Also, the RadCal absorption coefficient is from soot, CO, CO2, H2O, and fuel (for a small number of fuel types). If the frequency is primarily due to emissions from some other species (for example OH), then RadCal is not going to have the correct source term for that frequency.

[ETIENNE CHOPARD]

Thank you for your answer; I hadn't considered that issue. I thought of another possibility to solve my problem. I attempted to create my own 'air' species for the background and set the absorption coefficient to achieve the same effect as explained in the first message. I also set the emissivity of this new 'air' to 0 because I'm only interested in the flame, not the air contribution. However, I tried this approach following the instructions in the liquid droplet section of the User Guide (15.3).

&SPEC ID='MY AIR', EMMISSIVITY=0 ,RADIATIVE_PROPERTY_TABLE='radtab' [...] /
&TABL ID='radtab', TABLE_DATA= 1.0,0.00001,0.00001 /
&TABL ID='radtab', TABLE_DATA= 5.0,0.00001,0.00001 /

&TABL ID='radtab', TABLE_DATA= 5.1,100000,0.00001 /

&TABL ID='radtab', TABLE_DATA= 5.2,0.00001,0.00001 /

&TABL ID='radtab', TABLE_DATA=10.0,0.00001,0.00001 /

I tried it anyway, and FDS returned an error indicating that it was not well defined. It was predictable as the RADIATIVE_PROPERTY_TABLE is for PART and not SPEC... but i did not find anything similar fot SPEC. Do I have to use a RadCal species as a base for radiation properties? Is it impossible to create a completely new species or a species that doesn't match any of RadCal's existing ones?

Also, note that it is not important for me that the air react with the fuel of the flame.

[dr_jfloyd]

There is no equivalvent spectral input for a gas species.  FDS may not be the code for your problem. 

[dr_jfloyd]

You could try the wide band model and specify an additional narrow band for your frequency; however, you would still have the issue that depending on the primary source for that specific frequency you may not be correctly capturing the source term.