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Old   July 1, 2008, 13:57
Default Kinetic rates
  #1
Sally
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I have a two phase problem with mass transfer and reaction that I'm modellng. The problem has been converged in terms of the hydrodynamics, but in terms of the kinetic reactions and mass transfer going on, I'll have to solve for another 3 months before it converges.

It is so slow because of the ratio of feed rate into my geometry to the time step for the solver. What I really need to do is decouple these two in the solver.

I can't increase the physical timestep becasue it will crash the simulation.

Any suggestions on how I can converge quicker. Thanks for an help, sally.
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Old   July 1, 2008, 20:53
Default Re: Kinetic rates
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Karne de Boer
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Hey Sally I'm sure you've tried these things but I had similar problems and this was the advice given to me from the technical help:

- Get a complete converged solution and then turn on mass transfer and kinetics

- Turn on double precision in the solver settings

- Prove the concept on a simpler geometry (for example I am working on mass transfer and kinetics on a single tube reactor instead of the more complicated geometry)

You are probably aware of these but thought I'd share them anyway.

Have a good day Karne
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Old   July 2, 2008, 08:28
Default Re: Kinetic rates
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Sally
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Thanks Karne, it's good to share these things, I didn't know that the double precision setting would be usefull for speeding things up.

What I've also found out since posting, is that on the "Equation Class Settings" tab in the Solver option, it is possible to set the timestep for each equation class independently. So, it is possible to speed up the mass transfer and kinetic - rates of convergence by giving the mass fraction equation class a larger physical timestep than the momentum equations for example. In that way, the converged hydrodynamic solution is not perturbed while mass fractions are converging.

Thanks again, Sally.
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