# thermophysicalProperties with polynomial values

 Register Blogs Members List Search Today's Posts Mark Forums Read

March 12, 2016, 04:38
thermophysicalProperties with polynomial values
#1
Member

Join Date: Jul 2015
Location: Aalborg
Posts: 83
Rep Power: 10
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:
Code:
```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+cT˛+...
}
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)
}

}

// ************************************************************************* //```
Attached Images
 data-fit.png (14.9 KB, 204 views)

 March 12, 2016, 11:12 #2 Senior Member   Join Date: Sep 2013 Posts: 353 Rep Power: 20 Your polynomial seems wrong to me. http://www.wolframalpha.com/input/?i...rom+300+to+500

 March 12, 2016, 11:17 #3 Member   Join Date: Jul 2015 Location: Aalborg Posts: 83 Rep Power: 10 Hi Bloerb, you are absolutely right! I checked it, updated my data and the function and it works fine! Thank you very much!

July 5, 2019, 05:48
#4
Member

Priyanka P
Join Date: Apr 2019
Location: Germany
Posts: 40
Rep Power: 7
Quote:
 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

April 21, 2020, 10:51
#5
New Member

Join Date: Mar 2020
Posts: 2
Rep Power: 0
Quote:
 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

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post JMDag2004 OpenFOAM Pre-Processing 2 March 8, 2016 22:38 rv82 OpenFOAM Running, Solving & CFD 4 April 13, 2015 03:59 leroyv OpenFOAM Programming & Development 1 October 21, 2014 15:49 P1361 OpenFOAM Post-Processing 3 September 16, 2014 04:02 Wilesco Siemens 0 January 5, 2006 05:34

All times are GMT -4. The time now is 21:01.