[Gerrit]

Hi,

I am simulating heat transfer with hydrogen with buoyantSimpleFoam and my simulations with constant Pr -number went really well. As I use the results to validate values from a lab, I would like to come closer to reality. So I set up the polynomial thermophysicalProperties. That seems to works as well good for polynomial values of viscosity, density and thermal conductivity. But as soon as I use a polynomial function for Cp, the heat transfer is "switched off". The temperature at my outlet reaches inlet temperature - what is obviously wrong.
I really do not know why this happens, as the curve fit itself looks quite nice. If I use a constant value for Cp, the simulation gives again reasonable results.

Could someone help me with this or give a hint?

My thermophysicalProperties file looks like this:

thermoType
{
    type            heRhoThermo ;         // includes heat transfer
    mixture         pureMixture;          // pure Mixture
    transport       polynomial;            // polynomial
    thermo          hPolynomial;        // polynomial
    equationOfState icoPolynomial ;        // polynomial
    specie          specie;                // defines the specie
    energy          sensibleEnthalpy;        // form of energy
    dpdt         off;            // no pressure work in the solver
}

mixture
{
    specie
    {
        nMoles          1;            
        molWeight       2;          
    }
    equationOfState// rho(T)
    {
        rhoCoeffs<8>    
        ( 0.1701 -0.0003923 2.98e-07 0 0 0 0 0);// coef a + bT+cT²+...
    }
    thermodynamics
    {
        Hf              0;
        Sf              0;
        CpCoeffs<8>     (1.45e+04 26.14 -6.02 3.123 -1.577 0.4031 0 0);// Cp(T)
    }
    transport
    {
        muCoeffs<8>     (1.153e-05 1.112e-06 0 0 0 0 0 0);// viscosity(T) 
        kappaCoeffs<8>  ( 0.01771 0.0006152 -2.364e-07 0 0 0 0 0);//conductivity(T)
    }    
    
}

// ************************************************************************* //

[Bloerb]

Your polynomial seems wrong to me.

http://www.wolframalpha.com/input/?i...rom+300+to+500

[Gerrit]

Hi Bloerb,

you are absolutely right! I checked it, updated my data and the function and it works fine! Thank you very much!

[priyankap]

Originally Posted by Gerrit

Hi Bloerb,

you are absolutely right! I checked it, updated my data and the function and it works fine! Thank you very much!

Hi..


How you managed to calculate the values of coefficients for viscosity, conductivity etc, that you put in thermophysical properties?


Thank you

[IronArma]

Originally Posted by priyankap

Hi..
How you managed to calculate the values of coefficients for viscosity, conductivity etc, that you put in thermophysical properties?

Hi, I found this post late, but still I hope that it will be useful for future foamers.

To calculate the coefficients for viscosity and thermal conductivity it is sufficient to navigate the NIST webpage which seldom contains the values for dynamic viscosity and other relevant quantities recorded over a wide range of temperatures. Otherwise there's plenty of papers with these informations, it only requires luck to find a table of the values in a copy-paste enabled version. Then just perform a polynomial fit of whatever order best fits your desires.

Hope this is useful