I use ¡°DEFINE_SR_RATE¡± to define a custom surface reaction rate. It is one UDF of my source file. I have hooked this UDF in FLUENT panel successfully. What I try to do is to assign a certain consumption or production of a specified species. Question: Do I still need to define the ¡°finite rate¡± and ¡°mechanism¡± under the panel of ¡°Define-Materials-Reaction-finite rate and Mechanism¡±? If not, how this UDF is used in FLUENT because this surface reaction rate is only a general rate and does not mean how much the consumption or production of a specified species is. How to get the consumption or production of a specified species by this UDF? If it is need to define the ¡°finite rate¡± and ¡°mechanism¡±, what is relation between this UDF and ¡°finite rate¡±?

I had this same problem. When you specify the *rr value in DEFINE_SR_RATE you are specify the molar rate of production or consumption of the species.Once hooked, this takes precedance over the values in the the materials panel. Hope this helps.

Hi,andrew Could you explain in detail? I understand the *rr is the total surface reaction rate that have precedence, but how to define that it is one species reaction rate like H+ or OH-. I think i need to supply the stoichmetric coefficient somewhere. I don't know how to do that. By the way, if i want to define two different surface reaction rate on anode and cathode wall by this UDF, how to do that?

I am assuming that you have access to the manuals. If so the defining a reaction is explained in 4.3.16 of the UDF manual. As for defining reaction rate for several reactions, this can be done with a conditional if statement that is shown on this page. e.g.

if (STREQ(r->name, "reaction-1"))

*rr = [molar rate of production/comsumption]

eles *rr = [molar rate of production/comsumption]

As for speditying stoichmetric coefficients, I am unsure, but I believe that you will have to specify this in the UDF that you create. I believe that when you set *rr you are setting the value of Ri in equation 13.1-5.

Hi,Andrew I still have some confused. Let me make an example. Could you explain it? Thanks. I have a reaction H2+2(OH-) = 2(H2O)+2e- Now i define a surface reaction rate *rr . I want to let R(H2O)=K*Y(OH-) R(OH-)=-K*Y(OH-) Right now, i want to know how to set the relation between *rr and R(H2O), R(OH-). The "*rr" is the consumption rate of OH- ? or The "*rr" is the production rate of H2O.