Learning Forum

[曼曼 郝]

I defined the surface chemical reaction rate by writing udf and successfully compile and load it to fluent, and then connect udf to fluent solver by function hooks after selecting volumetric and wall surface under reactions in species transport. However, once the reaction is set, the Arrhenius rate gives the prefactor and activation energy by default, and this part feels conflicting with the chemical reaction rate defined by udf, what should I do with this part? 

[Judy Cooper]

In Fluent, reactions can be set up via an incoming mechanism, or by UDF.  The surface reaction UDF will override any existing surface reactions defined via the Species Model Reactions area, so if you are setting up surface reactions via UDF, all your surface reactions should be defined via UDF.  The same is true for volumetric (gas phase) reactions.

You can take a look at the Fluent Customization manual  DEFINE_SR_RATE UDF template to see an example of a surface reaction rate implementation.  Similarly, DEFINE_VR _RATE can be used to specify your gas phase reactions.

If you are reading in a surface or volume reaction mechanism and don't plan to use the REACTIONS in it, you can delete all the surface or volume reactions between REACTIONS and END of a particular mechanism to enter a dummy reactions that will allow Fuent to read in the other mechanism data without error.

 

Best Regards,

Judy

[曼曼 郝]

The UDF will cover all reaction mechanisms, does this mean I should include details of the species in the UDF, including concentrations and stoichiometric relationships, etc? Otherwise, the chemical reaction will not happen.

[Judy Cooper]

Reaction stoichiometry can be entered in the usual way, but any rates there will be ignored once the rate UDF is hooked.  The rate UDF should therefore reference all species involved in reaction and offer a rate for every reaction.