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Species transport for decomposition reaction

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Old   June 23, 2017, 01:18
Unhappy Species transport for decomposition reaction
  #1
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Achmad Rofi Irsyad
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Hello everyone

Currently, I am modeling thermal decomposition reaction of ZnO -> Zn + 0.5O2 inside a vertical cavity reactor with the staggered tube.
The heat comes from a window by irradiation discrete ordinate at 2,000 kW/m2. The cavity wall is set at 300 K.
The meshing already has suitable criteria.
Firstly, I turn off the species transport, only continuity by k-omega and energy equation, it converged at around 300 calculation.

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I am facing two problems right now.
1. I use species transport model with volumetric reactions. And then input the mixture-material (which is ZnO, Zn, and O2), finite-rate mechanism, and the input
number of reactant: 1, ZnO, stoch. coeff 1, rate exponent 1
number of product: 2, O2, stoch. coeff 0.5, rate exponent 1
Zn, stoch. coeff 1, rate exponent 1

Activation energy: 356 kJ/mol
pre-exponential factor: 4e9 ^-1

Then I define the fluid inside the tube as a mixture.
Then I go to boundary condition. The problem is when I edit the mass flow inlet in species tab, the option of material is defined as ZnO and O2 (even I don't mention O2 in the reaction mechanism of reactant, it is there).
And then in the outlet in species tab, it's the same (ZnO and O2), I cant find the Zn.
Where do I do wrong?

2. I just follow the flow in the number 1 (without defining Zn in the outlet) and got the divergence detected in AMG Solver: temperature.
Where do I do wrong when defining the species transport? Because previously its already converged.

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This is for my final year project. I am a newbie in CFD and Ansys Fluent.
I have already read the ansys tutorial, user, and theory guide but dont have a clue. If you can mention what material should I read through, please tell me.
Thank you very much in advance for your advice.
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Old   August 1, 2017, 12:26
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Bethany
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For #1, when you are in the Create/Edit Materials dialog box making your mixture-template for your inlet and outlet, you define your mixture species by clicking [Edit...]. This will open the Species dialog box, where you place the species you want in the mixture in the "Selected Species" box. The order you put your species in there matters - whichever one is last will be calculated based on the numbers you place for the other species. So, if you placed ZnO, O2, then Zn, Zn will not show up in the inlet/outlet mass species. However, if you put 0 for both ZnO and O2, then Zn will be 100% of the input.

This is brought up in the ANSYS Help in the "Overview of the Species Dialog Box," --> see the box labeled "Important." I am looking at the Help Viewer for Ansys 17.1

As for #2, I'm not sure. Sorry.
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chemical reaction, decomposition reaction, species transport, volumetric reaction

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