When I add a reaction, it diverges

Hello, everyone. I modified the Absorption_column_2d example of MFix.Tt’s about TFM,
Similar to a fixed-bed reactor. I turned off all the reactions in the example and add only one reaction, Reaction_1. The reaction rate is defined as a constant at Usr_rates, line510. When I turn the reaction off, the case works normally, and when I turn the reaction on, it diverges very quickly, showing DT<DTmin. When I try to set the reaction rate as a very small number, the calculation is very slow, and I guess it will end up diverging. Could you please help me check if there are some problems about the reaction rate in usr_rates or if there are other problems?
ann-again.zip (31.1 MB)
How can I solve this problem?

Hi @Chen_Boyan

Try enabling the stiff chemistry solver - when I turned this on, your case ran with Reaction_1 enabled.

But I’m not sure it makes sense for the reaction rate to be a constant - shouldn’t it depend at least on the concentration of the reactants?

– Charles

Thank you @cgw ,your method works! I have solve this problem!