## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### The reaction rate for a wall surface reaction

• WEI LI
Subscriber

Hello Ansys experts,

I am modeling a wall surface reaction. Consider the chemical reaction ongoing on a surface is A (species in fluid) + B (site species) --> C (solid species);

If I understand correctly, Ansys Fluent computes the reaction rate by R=k*c(A)*c(B), where k is the reaction constant, c(A) is the molar concentration in fluid in the unit [kmol/m^3] and c(B) represents the site density in the unit [kmol/m^2]. Neither the backward reaction nor coverage dependence was considered in this context.

k and c(B) are both just inputs from me, and they are not changing throughout the simulation period if I understand correctly. Notice that the temperature exponent and activation energy for reactions are both zero in the current simulation.

My question is

1. how Ansys Fluent selects c(A). Is it the molar concentration at the cell adjacent to the reaction surface?
2. If my understanding above is correct?

Thank you and regards

• Swathi V. V.
Ansys Employee

Hi ,

Please refer to the following user manaul page to know how rate of reaction is computed for surface reaction. Please refer to the equation 7-54.in 7.1.2. Wall Surface Reactions and Chemical Vapor Deposition (ansys.com)

C(A) is the Molar concentration of surface absorbed gaseous species on the wall

• WEI LI
Subscriber

Hi Swathi,

Thank you for your reply. However, I am still not quite sure about the difference between the molar concentration of surface-absorbed gaseous species on the wall and that at the cell adjacent to the wall.

The below image shows the molar concentration of A near the target wall. Can I say c(A)=5.7e-16 kmol/m^3?

Thank you and regards

• WEI LI
Subscriber

Also, I think it should be [Gi] instead of [Ci] in the equation 7-54.in 7.1.2. Wall Surface Reactions and Chemical Vapor Deposition (ansys.com), right?