I dont understand how a UDF for a reaction rate, which is attached to the appropriate function hook, is then attached to a reaction in the reaction panel. All I get are inputs for arrenhius reactions. Also, what if you have more than one reaction - there is only one function hook.

I know I am missing something basic but the manual does not address this issue.

I am using finite rate model, three species, two reactions.

When you supply a UDF for reaction rate, this happens: 1) Fluent calculates the reaction rate using the methods selected by you in the reaction panel, 2) the UDF you supplied is called, allowing you to modify the reaction rate. Since the UDF is called for every reaction, what you have to do is only modify the reaction rate for any reactions for which you do not want the default behavior.

To check for a specific reaction, you would look at the reaction structure (the variable "r" if you created your UDF using DEFINE_VR_RATE(name, c, t, r, mw, yi, rr, rr_t)). You can do something like this to check for a particular reaction:

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

modify rr here;

Joe