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Why doesn't my two-step chemical model work?[For H2+air reaction][finite rate model] |
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November 9, 2019, 13:28 |
Why doesn't my two-step chemical model work?[For H2+air reaction][finite rate model]
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#1 |
Senior Member
Join Date: Sep 2017
Posts: 130
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Guys,
I'm trying to use the two-step chemical model in my simulation. Here is the chemical mechanism: Here is the reference of the mechanism: https://www.researchgate.net/publica...-O2_combustion I wrote this CHEMKIN file: Code:
ELEMENTS O H N END SPECIES OH H2 O2 H2O N2 END REACTIONS H2+O2<=>2OH 2.3E+22 0.000 10202 2OH+H2<=>2H2O 1.83E+27 0.000 21992 END I imported the CHEMKIN file and it's ok but the solution and the residuals doesn't look ok. See: As you see the residuals of OH and H2O have oscilation. It should be noted that the solution is ok for one-step Hydrogen-air mechanism of Fluent. What's the matter with this mechanism? What's your opinion? How to solve it? |
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December 1, 2019, 09:28 |
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#2 |
Senior Member
Join Date: Sep 2017
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Rep Power: 8 |
No idea??????
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December 2, 2019, 01:01 |
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#3 |
New Member
Tamil Nadu
Join Date: Dec 2019
Posts: 11
Rep Power: 6 |
Hi Sir ,
I want to clarify how do you calculate activation energy value from the reference file you attached and the values you entered in chemkin file looks different??? Looks forward for the reply Many Thanks Sowmiya |
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December 2, 2019, 02:24 |
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#4 |
Member
samm
Join Date: Feb 2019
Location: South Korea
Posts: 39
Rep Power: 7 |
Check your units ,that may vary.
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December 2, 2019, 08:30 |
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#5 | |
Senior Member
Join Date: Sep 2017
Posts: 130
Rep Power: 8 |
Quote:
Thank you Sowmiya and Jegan for reply, Ok, let me tell you how I've written this CHEMKIN file. As it is said in this file (page No. 17): https://www.et.byu.edu/~tom/classes/...dentmanual.pdf The default units for A and activation energy are in terms of cm, sec, K, and moles. And also the Arrhenius equation is defined as(for CHEMKIN): https://www.researchgate.net/profile...image/ar-1.png As what is mentioned in the Article: https://www.researchgate.net/publica...-O2_combustion I attached a screenshot of the mechanism (table 1) that is mentioned in the article. http://uupload.ir/files/2ru4_dyfuhjklkk.png As you see in the screenshot, There are three parameters in the table; A, T, and n. I think that the authors of the paper didn't know that there are several forms of the Arrhenius equation. I attached the screenshots of three forms. Here are the images: https://www.researchgate.net/profile...image/ar-1.png https://www.researchgate.net/profile...image/ar-2.png https://www.researchgate.net/profile...image/ar-3.png Then I think the authors have made a mistake and the form of the Arrhenius equation for two-steps mechanism is this: https://www.researchgate.net/profile...image/ar-3.png Thus, T should be Tar. The unit of this parameter is K but for CHEMKIN file we need to convert it to cal/mole (convert Tar to Ea). Ok, Therfore we multiply Tar by the gas constant which is 1.98720425864083 (cal⋅K−1⋅mol−1). For example for the first reaction mechanism we have: 5134*1.98720425864083=10202 cal/mole For A, the units should be in terms of cm3, sec, and moles. Then we multiply A by 10e+6 to change the unit from m3.mol-1.s-1 to cm3.mol-1.s-1. Thus, e.g. we have: 2.3*10e+16*10e+6= 2.3*10e+22 This is the procedure that I've done to convert them. Do you see any problem? |
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January 12, 2020, 01:40 |
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#6 |
New Member
Tamil Nadu
Join Date: Dec 2019
Posts: 11
Rep Power: 6 |
Dear Sir,
Thank you for clarifying my doubts clearly. Also I want to know when you convert Ea in chemkin file to cal⋅K−1⋅mol−1 but the fluent should have the unit of Ea in J/ kgmol. How you are correlating the units? Looking forward for the reply. Many Thanks Sowmiya |
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January 12, 2020, 02:50 |
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#7 |
Member
samm
Join Date: Feb 2019
Location: South Korea
Posts: 39
Rep Power: 7 |
Convert your cal/mol value into J/kmol
or in mechanism file we can write REACTIONS CAL/MOLE This may work |
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