Defining Non-Arrhenius form of reaction rates in chemical kinetic mechanism

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  • Last Post 08 March 2019
Raghu posted this 06 March 2019

Hi,

 

I have a reaction rate for one gas phase reaction and it increases up to a certain temperature and the then decreases. We do not see this behavior generally. 

Any suggestion on how to represent this non-Arrhenius form in the Chemical kinetic mechanism?

Thanks,

Raghu

 

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sooraj546 posted this 07 March 2019

hi,

You can represent the reaction rate through UDF...............eg: VR_RATE........... etc. for single phase problems.

 

with regards

Sooraj

abenhadj posted this 07 March 2019

Thanks for the contribution!

Best regards,

Amine

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Raghu posted this 07 March 2019

Hi Sooraj,

Thanks for the reply.

But, I am wondering about defining it inside the chemical kinetic mechanism to use with CHEMKIN-Pro

Generally, we represent the rates with Arrhenius coefficients like A, n, and Ea and all the reactions rates in the mechanism are monotonically varies with temperature. Now, my case is a little different from those. Rate Increases up to a certain limit of temperature and decreases further. 

Any suggestions are welcome. 

Thanks,

Raghu

 

 

sooraj546 posted this 08 March 2019

Sinply define it through a UDF...............Eg Vr_Rate.

DEFINE_VR_RATE(volumetric_rate,c,t,r,mw,yi,rr,rr_t)

{.

./*............variable declaration..............*/

.real temp= C_T(c,t);/* in K*/

if (!strcmp(r->name, "reaction-1"))

{

if (temp<=848)

{

r2=k*(exp(-Em1/(R*temp)));/* Kmol/m3-sec*/

*rr_t=r2;

} etc............

thats all

 

with regards 

sooraj

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