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Fluids

Surface chemistry-Kinetic reaction rate is zero

    • ZoeYuan
      Subscriber

      Hi,


      I am modelling catalytic surface reaction using imported CHEMKIN mechanism in a single-channel model via ANSYS Fluent. The mechanism describes the oxidation reaction of CO, C3H6 and H2 as well as NO reduction by CO over catalyst surface site. 


      At the channel inlet, different mole fractions for species: O2, C3H6, H2, H2O, CO2, CO, NO were defined. At the channel wall, the reaction was activated with the surface area washcoat factor set as 70. 



      The simulation was set as transient simulation with gradually increased inlet temperature. After some iterations, the simulation finished without any errors with good convergence. I checked the species molar fraction at the outlet and noticed that there are reactions taking place. However, when plotting the contour of Kinetic Rate of Reactions, the reaction rate is zero for all the reactions. It is so weird, because there are definitely some reaction occuring. Take the CO conversion for example, the CO conversion efficiency obtained from simulation versus temperature is shown as below. CO is gradually consumed with temperature increasing; while related reaction rate is zero see screenshot attached below. Can anyone tell me is there anything wrong with my initial setting please?




      Regards,


      Zoe


       

    • ZoeYuan
      Subscriber

      Hi,


      Also, I have noticed that when setting the surface area washcoat factor as 1, the model has no convergence issue; while when changing the surface area washcoat factor to any other values, such as 10, 50, 70 etc, the model will diverge at a certain point (around inlet gas temperature=470 K). 


      The following figures show the simulation residuals and temperature plot. Can anyone have a look on this and give me some suggestions please? Thank you very much in advance. 





       


      Regards,


      Zoe

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