[nitz5]

hello everyone,
I am a Mtech student and currently doing simulation on downdraft gasifier. I am facing problems in putting reactions, pre-exponential factor and activation energy as iam new in this field. this is my first work on species transport.
how to get pre-exponential factor and activation energy ?
these are my reactions:
1. Vol + 0.174O2 + 0.457H2 ---> 0.268CO + 0.371H2O + 0.357H2 +0.003N2
Gas Phase Reaction
2. 2CO + O2 ---> 2CO2
3. 2H2 + O2 ---> 2H2O
4. CO + H2O ---> CO2 + H2
Particle Surface Reactions
5. C<s> + O2 ---> CO2
6. 2C<s> + O2 ---> 2CO
7. C<s> + 2H2 ---> CH4

if anyone wants more information about it please share with me...thank you!

[CeesH]

Typically from tables. In the basis these are measured values.
You can get some estimates, using collision theory for example (https://en.wikipedia.org/wiki/Collision_theory), but they come with significant error margins.

Some commentary from the wiki regarding activation energy:

"At a more advanced level, the net Arrhenius activation energy term from the Arrhenius equation is best regarded as an experimentally determined parameter that indicates the sensitivity of the reaction rate to temperature. There are two objections to associating this activation energy with the threshold barrier for an elementary reaction. First, it is often unclear as to whether or not reaction does proceed in one step; threshold barriers that are averaged out over all elementary steps have little theoretical value. Second, even if the reaction being studied is elementary, a spectrum of individual collisions contributes to rate constants obtained from bulk ('bulb') experiments involving billions of molecules, with many different reactant collision geometries and angles, different translational and (possibly) vibrational energies—all of which may lead to different microscopic reaction rates."

So, you're best off opening some book or database on these things

[lalannitw]

Firstly, when you turn on species transport then there below you have to define which type of reaction is this Volumetric, wall surface etc. Then define for turbulance- chemistry interaction which type of model you are using like eddy dissipation or finite rate eddy dissipation rate model by selecting model go to mixture material then edit and in edit section select all the mixture species then below in reaction press edit and give all the informations.

[nitz5]

thank you CeesH and lalannitw!
I will definitely try to use your suggestions and also thank you for giving your valuable time.
I will soon respond with pictures of my results and if I stuck in between I hope you will help me again.

[nitz5]

hello
iam not getting the maximum temperature.
i think there is no chemical reaction taking place inside the gasifier so that the heat is not released.