Learning Forum

[ss_stardust]

Hello,

   I want to model porous media with the LTNE energy model where radiation plays a significant role. I want to use an in-built radiation model but Ansys Fluent doesn't support such a combination.  So, I want to know if there is any alternate way to do so. Some papers which I have referred to mention the use of UDS via UDF but no clear explanation has been given. Any insight into the problem will be very much appreciated.

Thanks and regards

[Karthik Remella]

Hello You are correct - the non-equilibrium porous model is not available if the radiation models are enabled in Fluent.
Given this, unfortunately, looking through the literature would be the best way forward in this case. You might also want to connect with the authors of the paper to understand their formulation better. Sorry, I was not very helpful here.
Karthik

[rajendrapor]

Radiation within the porous media or ambient-porous media?

[ss_stardust]

Radiation within porous media
The basic model consists of porous medium as an absorbing, emitting and scattering medium through which participates with solar radiation while the heat transfer fluid which is passing though it acts as transparent.

[rajendrapor]

In my opinion, this type of modeling is done by implementing an effective thermal conductivity (k_eff) in the solid-phase energy equation. There are many correlations available for estimating this k_eff; however, kindly look for the correlation considering conduction and radiation in solids. Kindly see the following references for such correlation.
1) Breitbach, G., and H. Barthels. "The radiant heat transfer in the high-temperature reactor core after failure of the afterheat removal systems."Nuclear Technology49.3 (1980): 392-399.
2) Sih, S.S., Barlow, J.W., 1995. The prediction of the thermal conductivity of powders. 6th SFF Symposium, pp. 397ÔÇô401.
k_eff should be implemented as an UDF for the material property. Then a UDS is required for the solid medium.
Would you share the reference where they have used fluent for such simulation.

[ss_stardust]

Kindly see the following reference.
Villafán-Vidales HI, Abanades S, Caliot C, Romero-Paredes H. Heat transfer simulation in a thermochemical solar reactor based on a volumetric porous receiver. Applied Thermal Engineering. 2011 Nov 1;31(16):3377-86.

[rajendrapor]

1) The said reference has not mentioned the fluent version.
2) They have modeled the convection-radiation-species as source terms.
3) If you look closely, the solid phase energy equation has only conductive term and rest all heat-mass transfer terms are implemented as source terms.
This should be implemented as a UDS. where the source terms as well as the BCs (even k_eff) would be implemented as UDFs.
It's an excellent multiphysics problem. However, you will have to see the detailed theory in the fluent manual (of your version).
Kindly, note that fluent is just a tool to solve PDEs and it gives many features (e.g. UDS/UDF) for better control of physics involved in your problem.

BUT POINT IS WHY YOU WANT TO SIMULATE THE SAME MODEL IN FLUENT?

[ss_stardust]

I am trying to replicate the paper for my understanding. I am new to simulations in FLUENT and have limited knowledge of UDS/UDF. FLUENT UDF manual does provide with many examples which I have read but not able to apply for my case.

[rajendrapor]

In my opinion, being a beginner (as I am too) this type of multiphysics problem where all modes of heat transfer and reaction kinetics should not be solved at first.
Start with a LTE model (simultaneously seeing the fluent theory, user guide and UDF manual). Try to implement small UDFs, like material properties, BCs, source terms etc.
Then switch to LTNE model. This will help to implement UDS for solid temperature calculation.
Then combine LTE+P1 radiation (or any other) model. Implement UDS/UDF as desired.
Till this point, it would be clear to you how fluent behaves and handles the equations. Now you can simulate LTNE with source terms.
Although, LTNE model is not explained in detail anywhere. One can gain experience by practice only.

[ss_stardust]

Thanks for the help and suggestions.