reactingFoam: Reactions with hydrogen, questions about chemical and thermophysical parameters

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Raedchen_im_System
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reactingFoam: Reactions with hydrogen, questions about chemical and thermophysical parameters

Post by Raedchen_im_System »

On youtube, I published a tutorial about simple combustion with CfdOf. The solver is reactingFoam. The video can be seen here: https://youtu.be/TnPm4SVmdp0

In the comments, I received the following question from the user Tobias Jacobsen (@habahabahabahabahaba):
is there any chance you could show it with a hydrogen combustion example?
My answer is: For my tutorial, I took all parameters from the openFoam-/reactingFoam-tutorial because this was the fastest and easiest way to build up the files for the tutorial.

For changing the chemical reaction from methane to hydrogen, you have to change the chemical elements in the directory "0". This should be quite easy. It is more complicated to get the parameters for the directory "constant":
  • the file "thermo.compressibleGas" contains Information about molWeights, thermodynamics and transport
    • The molWeight is more or less self-explaining (for hydrogen it is 1,00794 g/mol).
    • I have no idea why the specific heat capacity cp consists of 6 columns per temperature, probably this is for interpolation.
    • The transport parameters As and Ts are totally unknown for me.
  • for the "reactions" file, you must know the parameters of the Arrhenius-equation. I did not found any description of the specific Arrhenius-equation used in reactingFoam, but it seems that the Arrhenius-equation is temperature-sensitive.
Majid Mansouri Borujeni and Hamid Reza Norouzi (Link: https://www.cemf.ir/PDFs/OpenFOAM/Sandi ... ngFoam.pdf) describe that data from the program "Chemkin" can be transformed into reactingFoam via chemkinFoam. "Chemkin" (Link: https://en.wikipedia.org/wiki/CHEMKIN) is a commercial software distributed by Ansys. I do not have access to "Chemkin", so I can't give you any further information.

Question to the Forum: Has anybody an idea where to find ...
  • the thermophysical parameters for "thermo.compressibleGas"?
  • the parameters of the Arrhenius-equation for reactions with hydrogen?
Has anybody a detailed description on the input parameters of reactingFoam and the units?
tobias_jacobsen
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Joined: Sun Apr 23, 2023 9:00 pm

Re: reactingFoam: Reactions with hydrogen, questions about chemical and thermophysical parameters

Post by tobias_jacobsen »

]Hi mister Raedchen (@Tech Bernd):
Temp_burner.0006.png
Temp_burner.0006.png (199.42 KiB) Viewed 1418 times
Temp_burner.0012.png
Temp_burner.0012.png (125.26 KiB) Viewed 1418 times
thank you veru much for the response. This tutorial has been very helpful.

I have managed to create a slight modification to the geometry, by following your guide.

I unfortunately do not have access to Chemkin either, but it seems that the python package Cantera: https://cantera.org
Might be able to find the constants.
I am still very much a novice at both combustion and fluid dynamics, so I have not worked out yet how find the correct reaction rates.
I have taken some tutorial files from Cantera, and managed to find something close to the burner setup, although this is for a premixed setup.

If the python code could be of interest, I will of course share it.
CH4.png
CH4.png (152.16 KiB) Viewed 1418 times
There seems to be some forums stating that openfoam can use cantera, but I have yet to find any examples of this.

Thank you very much for the papers, I will try to show this to my professor, and see if he has some ideas.
Last edited by tobias_jacobsen on Sun Apr 23, 2023 9:33 pm, edited 1 time in total.
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Raedchen_im_System
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Re: reactingFoam: Reactions with hydrogen, questions about chemical and thermophysical parameters

Post by Raedchen_im_System »

I've had some time to poke around the internet, and I found a very good tutorial about reactingFoam. This tutorial explains all formulars and all parameters for reactingFoam: https://www.tfd.chalmers.se/~hani/kurse ... ngFoam.pdf
.
############################################################
.
Arrhenius.JPG
Arrhenius.JPG (10.49 KiB) Viewed 1279 times
The parameter A is the pre-exponetial factor, beta is the exponent to temperature and Ta is the activation energy. I found 1 source for the parameters: http://www.hysafe.org/img/fhslect03.pdf
A = 1.8e13, b = 0, Ta = 73745
.
############################################################
.
CP Values.JPG
CP Values.JPG (24.93 KiB) Viewed 1279 times
The specific heat capacity cp depending on temperature is given in this source: https://webbook.nist.gov/cgi/cbook.cgi ... G&Table=on

The values for cp/R can be approached by a polynom:
y = -3.34674237E-08x2 + 5.03525406E-04x + 3.23332672

With these numbers, the block “thermodynamics” of H2 in the file thermos.compressibleGas looks the following:

thermodynamics
{
Tlow 298
Thigh 6000;
Tcommon 3000;
highCpCoeffs ( 3.23332672 5.03525406E-04--3.34674237E-08 0.0 0.0 0.0 0.0 );
lowCpCoeffs ( 3.23332672 5.03525406E-04--3.34674237E-08 0.0 0.0 0.0 0.0);
}

.
############################################################
.
Sutherland.JPG
Sutherland.JPG (10.02 KiB) Viewed 1279 times
The „transport“ properties are given via a special Sutherland-formula. The Sutherland-formula is described in Wikipedia: https://en.wikipedia.org/wiki/Temperatu ... _viscosity

In the German version of Wikipedia (https://de.wikipedia.org/wiki/Sutherland-Modell), the parameters for the Sutherland-formula are given. These parameters can be transformed into the version of reactionFoam. The parameters for the Sutherland-equations are:
Ts = 72
As = 6.36236562420E-01

The properties for transports are:
transport
{
As 6.36236562420E-01;
Ts 72;
}


Other useful sources:
https://www.engineeringtoolbox.com/hydrogen-d_976.html
https://cefrc.princeton.edu/sites/g/fil ... netics.pdf
https://doc.comsol.com/5.5/doc/com.coms ... 08.27.html

I hope that your model with hydrogen is now running. It would be nice if you post your results and your experiences here as well - please always remember that this forum lives on give and take. Could you tell us what tips or hints you got from your professor?
tobias_jacobsen
Posts: 2
Joined: Sun Apr 23, 2023 9:00 pm

Re: reactingFoam: Reactions with hydrogen, questions about chemical and thermophysical parameters

Post by tobias_jacobsen »

Hi mr Raedchen

Sorry for the late reply, It is currently the exam season in DTU.

So most of the professor's time has gone to preparing the exam.

I have been given some reading material and self study material.

I was introduced to - 12 steps to CFD by Lorna Barbara
https://www.youtube.com/watch?v=cDy5XGO ... University

The course covers the finite difference method.
To my understanding OpenFOAM uses finite volume, but it seems as if finite volume is but an extension to finite difference.

I was told to continue retrieving data from Cantera.
It seems that the primary data, that the CFD needs from the combustion chemistry model is heat release rate and density change before and after the combustion.

It seems that the reason the airflow accelerates after the combustion is because of the associated drop in density.
A fundamental assumption of the burner is that the flow is stationary.
so if the density drops the velocity of the flow must increase.

Combustion chemistry is difficult to describe, so I was introduced to CFD - combustion and CFD applications
https://www.youtube.com/watch?v=9OjUoAF ... nnel=CEFRC

Thank you very much for the help, it has been very diffficult to navigate the use of openFOAM.

as soon as I have a simulation that seems reasonable I will post it on this forum.
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