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-   -   CFX5.7 - chemical reaction problem... (http://www.cfd-online.com/Forums/cfx/20743-cfx5-7-chemical-reaction-problem.html)

H.L. October 23, 2004 04:16

CFX5.7 - chemical reaction problem...
 
Dear Sir:

I create one Water Gas Shift reaction in CFX-Pre as follows: But After finishing CFX-Pre and preceed to CFX-Solve, one error occurs in the next following paragraph. I have set the unit to [s^-1} already, but error still occurs again and again, although I ducplicate other good reaction to modify and reset.

Anyone know what's up with my reactions ?

Thanks for your help!!!

H.L.

--------------------------------------

REACTION: Water Gas Shift reaction

Option = Single Step

BACKWARD REACTION RATE:

Option = Arrhenius

Pre Exponential Factor = 2.65e-2[s^-1]

Temperature Exponent = 0

REACTION ACTIVATION:

Activation Energy = 3.96 [J mol^-1]

Option = Activation Energy

END

END

FORWARD REACTION RATE:

Option = Arrhenius

Pre Exponential Factor = 2.75E9 [s^-1]

Temperature Exponent = 0.

REACTION ACTIVATION:

Activation Energy = 8.38E4 [J mol^-1]

Option = Activation Energy

END

END

PRODUCTS:

Materials List = CO2,H2

Option = Child Materials

CHILD MATERIAL: CO2

Option = Stoichiometric

Stoichiometric Coefficient = 1.0

END

CHILD MATERIAL: H2

Option = Stoichiometric

Stoichiometric Coefficient = 0

END

END

REACTANTS:

Materials List = CO,H2O

Option = Child Materials

CHILD MATERIAL: CO

Option = Stoichiometric

Stoichiometric Coefficient = 1.0

END

CHILD MATERIAL: H2O

Option = Stoichiometric

Stoichiometric Coefficient = 1.0

END

END

END

-----ERROR----------------------------------- Error in setting: ""Pre Exponential Factor"" via the expression: 2.75E9 [s^-1] Error detected at the end of the expression. Expression has wrong dimensions required units: m^3 s^-1 mol^-1, expression's units: s^-1. Error processing expression: Pre Exponential Factor = 2.75E9 [s^-1] +--------------------------------------------------------------------+ | An error has occurred in cfx5solve: | | | | C:\CFX\CFX-5.7\bin\winnt\ccl2flow.exe exited with return code 3. | +--------------------------------------------------------------------+


Jeff October 23, 2004 10:28

Re: CFX5.7 - chemical reaction problem...
 
Your forward and backward reactions are:

R(forward) = kf[CO][H2O] R(backward) = kb[CO2] {[H2] order 0}

The kf and kb, necessarily need to be in different units, because they are being multiplied by different multiples of concentrations.

There error message here is telling you the units you should be using. To cancel out the extra concentration multiplier {mol/m^3} your kf needs extra units of {m^3 mol^-1 s^-1}. This will give a final rate in mol m^-3 s^-1.

Jeff

H.L. October 23, 2004 22:51

Re: CFX5.7 - chemical reaction problem...
 
Thanks, Jeff!!! I got it and find the document...

regards,

zolrack March 24, 2009 19:02

you must to delete de order of reaction in one of the reactant in order to get a first order reaaction otherwise ou will need a second order units for arrhenius equation

cfdguy March 25, 2009 11:33

Back from the dead thread? ;)


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