I am modelling porous medium combustion in FLUENT with a separate energy equation for the fluid and the solid zone. Since the temperature of the solid region is quite high (around 1200 K), radiation is expected to have significant effect on the preheating of the inlet charge. I do not specify the actual solid-fluid phase boundaries in FLUENT. It is just a region that is specified as porous in a volume averaged sense. How do I include radiation effects from such a region?
Is there a direct option in FLUENT or would I have to write a UDF ? If so, can I get some suggestions on how to implement it ?
The impact of radiative heating will depend upon the phase of the fluid (gas or liquid), its absorption properties, and the residence time of the fluid in the porous space. I don't think there is a direct option to handle this in FLUENT so you would need to write some simple algorithm to account for this portion of the heating....Depending upon the fluid, the radiative component could be small compared to heat transfer between the solid surface and the fluid, especially for gases.
It is the radiation in solid phase, that is surface to surface, matters.
You could possibly consider using the Discrete Ordinate model of radiation and tricking the radiation to treat the different phases by playing with absorption, transmission and reflection properties of the individual phases - but you won't have much physical guidance as to what to set these properties to.
Otherwise, as Dave says - you will need to create a UDF function.
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