KR346: How to set a reaction rate affected by a catalyst in CFX-Pre?


Before formulating the affect of a catalyst on a reaction rate, it is imperative to look into the way in which a catalyst affects a reaction.

A catalyst is a substance which affects a reaction rate but does not participate in it. A catalyst simply acts to add or remove momentum from the collision it undergoes with the reacting species.

The effectiveness of a catalyst in doing this goes linearly with its local concentration under normal pressures ( Note that at high pressures there could be multiple collision events in which case the rate is not linearly proportional to its concentration)

Keeping in mind the above, catalyst affect can be set up in CFX in the following two ways:

(1) Default CFX Formulation: Use Third Body Option.
Net Reaction Rate = Summation [Efficiency * (Catalyst Concentration) ]*Reaction Rate
This method incorporates the linear effect of the catalyst.

(2) Incorporate the Catalyst in the Arrhenius Rate itself (allows incorporation of non-linear catalyst effects):

- Make the Catalyst, a REACTANT with a ZERO Stoichiometry and appropriate order.
Note that in this scheme, if there are multiple catalysts, one has to define separate reactions for each catalyst. The default CFX formulation, item (1), allows the inclusion of multiple catalysts in one step.





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