CHEMKIN surface reaction import in ANSYS FLUENT

cfdkorea · April 22, 2016, 07:05

Hi can anyone tell me how fluent convert the units of preexponential while importing data from chemkin to fluent. specially conversion of sticking coefficient into preexponential. I will be thankful

LuckyTran · April 25, 2016, 02:57

Note: All quantities for the Arrhenius rate parameters are in units of kgmol, m3, and seconds.

Important: It is important to note that if you have selected the British units system, the Arrhenius factor should still be entered in SI units. This is because ANSYS Fluent applies no conversion factor to your input of Ar (the conversion factor is 1.0) when you work in British units...

cfdkorea · April 26, 2016, 03:16

well thanks for your reply. i have pre exponent constant in units of cm2/mol-sec and 1/sec. can i put it as it is in the fluent.

LuckyTran · April 26, 2016, 09:03

No. You must convert to kmol m^3.

Unless you've changed the Fluent display units.

cfdkorea · April 26, 2016, 10:13

Any guess how can I convert from cm2/sec to Kmol/m3.

villager · August 16, 2016, 12:36

FLUENT performs units conversion during CHEMKIN mechanism import at least when you use default SI units.

The answer is "Yes", if you use File -> Import CHEMKIN mechanism, and if you've specified site density in mol/cm2 (!) in your input file.

Example:
SITE/PLATINUM/ SDEN/2.07E-9/
....
CO(S) + Pt(S) => C(S) + O(S) 1e+21 0.0 200.0
....

Then, FLUENT would display your surface site density as 2.07e-08 in kmol/m2 under Species -> Mechanism
and your preexponent
1e+21 would be treated as in cm2/mol/s, -> * 2.07e-09 to convert to 1/s, then *2.07e-08 to convert back to m2/kmol/s.

And you would see 1e+20 m2/kmol/s for preexponent under Species -> Reaction -> your Reaction (pretty much units, yes?)

jumaah · August 20, 2016, 21:56

the pre-exponential value depends on the number of reactions, so when you import mechanism from Chemkin to fluent, the value will change. usually divided by (10^3) for bimolecular reaction, the unit (cm3/mol.s) ; and by (10^6) termolecular reaction, the unit (1/s).
I am not 100 percent sure if this answered your question. I hope this will help

YNREDDY · March 27, 2017, 15:42

Can anybody explain how is fluent converting the units for adsorption reaction of the kind
H2 + Pt(s) + Pt(s) => H(s) + H(s) 4.600E-02 0.000 0.000
STICK FORD/Pt(s) 1/
where the order w.r.t Platinum is 1.
If the order is 2 it calculates pre exponential factor according to the expression So/sitedensity^2*(RT/2*pi*M) in prescribed units, which is coming right according to my calculation, but not the former case applying the same formula with So/sitedensity^1*(RT/2*pi*M) .
Please explain!!.. along with the units if possible.

Thanks

Weiqiang Liu · March 17, 2018, 11:38

I imported chemkin format mechanism of gas and surface reactions into Fluent.
however, the solver keeps popping up 'received a fatal signal (segmentation error)'
The mechanism definitely has no problem. Because I copied them from Chemkin package. Does anyone know what is the possible reason that causes this error?

April 22, 2016, 07:05	CHEMKIN surface reaction import in ANSYS FLUENT	#1
cfdkorea New Member anonymus Join Date: Apr 2016 Posts: 11 Rep Power: 10	Hi can anyone tell me how fluent convert the units of preexponential while importing data from chemkin to fluent. specially conversion of sticking coefficient into preexponential. I will be thankful

April 25, 2016, 02:57		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,764 Rep Power: 66	Note: All quantities for the Arrhenius rate parameters are in units of kgmol, m3, and seconds. Important: It is important to note that if you have selected the British units system, the Arrhenius factor should still be entered in SI units. This is because ANSYS Fluent applies no conversion factor to your input of Ar (the conversion factor is 1.0) when you work in British units... cfdkorea likes this.

August 16, 2016, 12:36		#6
villager Member vlg Join Date: Jul 2011 Location: My home :) Posts: 81 Rep Power: 18	FLUENT performs units conversion during CHEMKIN mechanism import at least when you use default SI units. The answer is "Yes", if you use File -> Import CHEMKIN mechanism, and if you've specified site density in mol/cm2 (!) in your input file. Example: SITE/PLATINUM/ SDEN/2.07E-9/ .... CO(S) + Pt(S) => C(S) + O(S) 1e+21 0.0 200.0 .... Then, FLUENT would display your surface site density as 2.07e-08 in kmol/m2 under Species -> Mechanism and your preexponent 1e+21 would be treated as in cm2/mol/s, -> * 2.07e-09 to convert to 1/s, then 2.07e-08 to convert back to m2/kmol/s. And you would see 1e+20 m2/kmol/s for preexponent under Species -> Reaction -> your Reaction (pretty much units, yes?) Last edited by villager; August 20, 2016 at 22:23.*

March 27, 2017, 15:42	Units of pre exponential factors	#8
YNREDDY New Member YNREDDY Join Date: Mar 2017 Posts: 4 Rep Power: 9	Can anybody explain how is fluent converting the units for adsorption reaction of the kind H2 + Pt(s) + Pt(s) => H(s) + H(s) 4.600E-02 0.000 0.000 STICK FORD/Pt(s) 1/ where the order w.r.t Platinum is 1. If the order is 2 it calculates pre exponential factor according to the expression So/sitedensity^2(RT/2piM) in prescribed units, which is coming right according to my calculation, but not the former case applying the same formula with So/sitedensity^1(RT/2piM) . Please explain!!.. along with the units if possible. Thanks

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April 26, 2016, 03:16		#3
cfdkorea New Member anonymus Join Date: Apr 2016 Posts: 11 Rep Power: 10	well thanks for your reply. i have pre exponent constant in units of cm2/mol-sec and 1/sec. can i put it as it is in the fluent.

April 26, 2016, 09:03		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,764 Rep Power: 66	No. You must convert to kmol m^3. Unless you've changed the Fluent display units.

April 26, 2016, 10:13		#5
cfdkorea New Member anonymus Join Date: Apr 2016 Posts: 11 Rep Power: 10	Any guess how can I convert from cm2/sec to Kmol/m3.

August 20, 2016, 21:56		#7
jumaah Member Omar jumaah Join Date: Jan 2016 Posts: 36 Rep Power: 10	the pre-exponential value depends on the number of reactions, so when you import mechanism from Chemkin to fluent, the value will change. usually divided by (10^3) for bimolecular reaction, the unit (cm3/mol.s) ; and by (10^6) termolecular reaction, the unit (1/s). I am not 100 percent sure if this answered your question. I hope this will help

March 17, 2018, 11:38		#9
Weiqiang Liu Senior Member Weiqiang Liu Join Date: Feb 2018 Posts: 278 Rep Power: 9	I imported chemkin format mechanism of gas and surface reactions into Fluent. however, the solver keeps popping up 'received a fatal signal (segmentation error)' The mechanism definitely has no problem. Because I copied them from Chemkin package. Does anyone know what is the possible reason that causes this error?