Specifying Surface Reactions in the Reaction Mechanism

The surface reaction UDF DEFINE_SR_RATE is hooked to a surface reaction in Ansys Fluent. The rate for that surface reaction is always zero, no matter what is specified in the UDF. Also, if both Arrehnius coefficients (via GUI) and DEFINE_SR_RATE is specified for a surface reaction, which will take precedence?

The reaction is likely missing from the reaction mechanism. Surface reactions must be included in the reaction mechanism by editing the mechanism in the Mixture Template. There, make sure that the Reaction Type is set to "All" so that the surface reaction can be included in the mechanism. UDFs that are hooked and apply to a given surface reaction will take precedence over any coefficients that are defined in the GUI.