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-   -   Heat conduction problems in OF220 (http://www.cfd-online.com/Forums/openfoam-solving/114931-heat-conduction-problems-of220.html)

Nico A. March 20, 2013 04:47

Heat conduction problems in OF220
 
1 Attachment(s)
Hello FOAMers,

I actually want to simulate a cht problem with many different regions in OpenFOAM 2.2.0. But when I simulated a little test case, there occur differences in heat conduction from OF 2.1.1 to 2.2.0. You can therefore have a look at the attached picture.

I took the flange case out of the laplacianFoam tutorial. Then I adjusted the material properties for cp, rho and kappa in this way that I should get the same results for laplacianFoam solver and chtMultiRefionFoam solver. (In laplacianFoam we have just DT, which can be calculated as: DT = kappa/(cp*rho) )

The results for laplacianFoam and cht - OF211 simulation are similar. Unfortunately the cht - OF220 simulation differs from that.

So my question is, does anyone know what the problem is in this case? Is it maybe a bug of the new version?

Best regards, Nico

Nico A. March 20, 2013 05:35

I also looked at the source code of solveSolid.H in the cht solver. The TEqn for OF211 is:
Code:

for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++)
    {
        tmp<fvScalarMatrix> TEqn
        (
            fvm::ddt(rho*cp, T)
          - fvm::laplacian(kappa, T)
        );
        TEqn().relax();
        TEqn().solve(mesh.solver(T.select(finalIter)));
    }

For the hEqn in OF220:
Code:

for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++)
    {
        tmp<fvScalarMatrix> hEqn
        (
            fvm::ddt(betav*rho, h)
          - fvm::laplacian(betav*alpha, h, "laplacian(alpha,h)")
          ==
            fvOptions(rho, h)
        );

        hEqn().relax();

        fvOptions.constrain(hEqn());

        hEqn().solve(mesh.solver(h.select(finalIter)));

        fvOptions.correct(h);
    }

So in the new version there is an additional fvOptions term which I do not use. And enthalpie h is used instead of temperature T. I just don't understand what betav is supposed to mean. Can someone exlain this value?

Once more, best regards, Nico

abigail158 June 15, 2013 07:37

Hi Nico A,

i'm also interested in solving multiregion heat transfer and currently testing the solver chtMultiRegionFoam. Have you figured out what 'betav' in createSolidFields.H means?
Thx!

mxylondon September 4, 2013 13:38

I am working on this issue as well. They should be the same things, but still don't understand what 'betav' is.

vitors March 12, 2014 13:10

I'm also interested in understanding betav and fvOptions(rho, h).

Waiting for the enlightenment...

akrasemann March 14, 2014 07:07

fvOptions is a utility enabling you to introduce additional terms into the solver, as far as I understand the release notes http://www.openfoam.org/version2.2.0/fvOptions.php.

Regarding the solid region within chtMultiRegionFoam I'm as well curious about the exact meaning of betav.

In German textbooks on (solid body-) mechanics the thermal volumetric expansion coefficient is sometimes called beta_v, but I do not understand, why this coefficient should be introduced into the solver.

vitors March 14, 2014 10:21

Quote:

Originally Posted by akrasemann (Post 479988)
fvOptions is a utility enabling you to introduce additional terms into the solver, as far as I understand the release notes http://www.openfoam.org/version2.2.0/fvOptions.php.

Regarding the solid region within chtMultiRegionFoam I'm as well curious about the exact meaning of betav.

In German textbooks on (solid body-) mechanics the thermal volumetric expansion coefficient is sometimes called beta_v, but I do not understand, why this coefficient should be introduced into the solver.

Thanks akrasemann,

Actually, I just removed fvOptions(rho, h) from my solver and added a source-term manually. However, I'm still curious on how it works internally. I could check it manupulates a list of pointers to contents in the fvOptions file, but sometimes I have to hold the impetus of try to understand everything in OpenFOAM and just do what I need.

Thanks a lot for your help. I'll do the homework researching on "thermal volumetric expansion coefficient" (at this point you probably realized I'm not an engineer) but please, keep us updated if you get more information about the betav in the solver.

Thank you!


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