[PostProcess] Qdot - related to Arrhenius-kinetics?

alainislas · April 17, 2021, 14:35

Hello everyone

I am working my case with coalChemistryFoam, solving for some gas and particle reactions. I am interested in knowing what is the total heat release of my reactions (in Joules). OpenFOAM exports Qdot in units [J / (m^3 s)]. Hence, I assume I can simply perform:

$\text{Total Heat Release} = \sum_{j=1} \left[\sum_{i=1} \text{Q}_\text{dot} dV_{i} \right] dt_{j}$

For the volume integral, I am using a volIntegrate operation in my controlDict.

Code:

functions
{

	volFieldValue1
	{
	    type            volFieldValue;
	    libs            ("libfieldFunctionObjects.so");

	    log             yes;
	    writeControl    timeStep;
	    writeInterval	1;
	    writeFields     true;

	    regionType      cellZone;
	    name            FLUID_SPHERE; //<-- This is my whole domain
	    operation       volIntegrate;

	    fields
	    (
		Qdot
	    );
}

Then I can simply integrate over time. However, I am testing various Pre-exponential factors and Activation Temperatures, and Im getting different values for the Heat Release. I don't see the dependency of the Heat Release with Arrhenius-kinetics.

Does anyone know if Im treating Qdot correctly?

heheda · November 22, 2021, 10:32

Can you please tell me what the full command for Qdot is? I use "postProcess -func Qdot" but it gives me an error. Thank you very much!

Marpole · December 2, 2021, 00:24

You can do it with a post-processing command below. But it doesn't work properly. The results are all zero. I guess its a bug.

Code:

reactingFoam -postProcess -func Qdot

You can also do it in run-time by putting the following at the end of file controlDict. It works fine. The unit is J/m^3-s. So the number is very large and varies a lot cell by cell. The flame contour plot is not very smooth.

Code:

functions
{
    #includeFunc Qdot
}

Marpole · December 2, 2021, 00:46

If you want to get the total heat release rate, one way to obtain it without programming is to use integrateVariables and plotDataOverTime features of paraFoam or paraview. When you do integrate, don't turn on "Divide Cell Data by Volume". And you do plotDataOverTime, select "Cells" in Field Association. After you plot it out, you can "save data" to get the trace.

November 22, 2021, 10:32	dear alainislas	#2
heheda New Member wangh Join Date: Jul 2020 Posts: 10 Rep Power: 6	Can you please tell me what the full command for Qdot is? I use "postProcess -func Qdot" but it gives me an error. Thank you very much!

December 2, 2021, 00:24		#3
Marpole Senior Member Charles Join Date: Aug 2016 Location: Vancouver, Canada Posts: 151 Rep Power: 10	You can do it with a post-processing command below. But it doesn't work properly. The results are all zero. I guess its a bug. Code: reactingFoam -postProcess -func Qdot You can also do it in run-time by putting the following at the end of file controlDict. It works fine. The unit is J/m^3-s. So the number is very large and varies a lot cell by cell. The flame contour plot is not very smooth. Code: functions { #includeFunc Qdot } __________________ Charles L.

December 2, 2021, 00:46		#4
Marpole Senior Member Charles Join Date: Aug 2016 Location: Vancouver, Canada Posts: 151 Rep Power: 10	If you want to get the total heat release rate, one way to obtain it without programming is to use integrateVariables and plotDataOverTime features of paraFoam or paraview. When you do integrate, don't turn on "Divide Cell Data by Volume". And you do plotDataOverTime, select "Cells" in Field Association. After you plot it out, you can "save data" to get the trace. __________________ Charles L.