Learning Forum

[rajendrapor]

For a case of flow and heat transfer through a porous media (or even a simple pipe), what is the entropy generation formulation used by Fluent? (Viscous dissipation is neglected in the case). The flow is laminar. Similarly, for pure conduction cases any refrence for the same.

[Kishan Konannavar]

Hello
Could you share in what context are you asking this question, as in, what specific problem are you trying to solve?
Thank you
Kishan

[rajendrapor]

Thanks for the prompt response!!
I wish to know the equation(s) Fluent uses to calculate the entropy generation for a case of flow (Delta P) and heat transfer (conduction & convection) through a porous media for laminar flow (viscous dissipation is neglected). Some references would also be highly appreciated. Since, without any proper reference in the user manual of Fluent (or anything similar) about the rate of entropy generation, one cannot adopt Bejan's formulations.

[Kishan Konannavar]

Hello
Fluent does not calculate the entropy generation, it is a derived quantity. You might want to look into references for the exact formula to derive the same. Unfortunately I would not be able to point you to that. The general formula would be: dynamic viscosity *(shear strain rate)^2. You may have to extract the quantities necessary for the calculation of the entropy generation. You might want to look into UDFs for that.
Thank you
Kishan.

[rajendrapor]

Thanks for the response!!
The equations are well established and are given in A. Bejan's books/papers. So, I can write the UDF for post processing the results in form of entropy generation.

[MONAGAD]

could you write the entropy generation equation you use?

[MONAGAD]

Is there any quality in fluent calculate this equation directly?

[Rob]

Check the Custom Field Functions, there are some derivative available there. Otherwise you may need a UDF. Expressions are becoming more powerful, but I don't think they can handle the derivatives etc just yet.

[MONAGAD]

Thanks for your reply, I appreciate it, I find that it is called viscous dissipation term in the fluent theory but still can't find this term directly in fluent, I just find turbulence dissipation but not viscous dissipation, Do you have any suggestion?

[Rob]

Check the general equations - I suspect it's part of the more general flow solver theory.

[MONAGAD]

It is part of energy equation, and I need to know if there any parameter calculate it directly in fluent

[MONAGAD]

This viscous term is also part of entropy equation, i can define all other parameters in this equation in user define function but this disipation term do not know from where get it

[Rob]

If it's not in the UDF manual we can't assist due to the Forum rules. Have you checked the header files?

[MONAGAD]

Thanks again for reply,but what do you mean with the header files?

[Rob]

The .h files - they contain the macros.