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X1t - time


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I'm having some trouble with X1t not simulating through the specific time range that I want it to. I have my model set-up to model from 0 to 1000, with an inlet-2 at 10 years. I noticed that when I take out my Kinetic Calcite out of the "Reactants" pane, it simulates all the way through. But when I leave it in there, it simulates to 1 minute. I have 89% Calcite. The other 11% doesn't really matter. I'm just wondering why it isn't simulating to 1000 years?

 

I have also attached the model.

 

Thank you,

 

Jay

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Hi Jay,

 

The problem is that you're using kinetics to model an incredibly fast reaction over a long period of time. This forces the program to take tiny timesteps, eventually causing it to crash. Try doing a "Go Initial" for this example, and take a look at the Calcite dissolution rate in the first node - it's huge. If your formation is mostly Calcite, set it as an equilibrium mineral (swap for Ca++ or HCO3-, for example) in the Initial pane.

 

You should look into what's called the Damkohler number (Da), which represents the rate at which a component reacts chemically relative to the rate at which it is transported by advection. In your example you've specified a very fast reaction and a very slow flowrate (0.0001 m head drop across a 1000 m domain). This results in a very high Da, which indicates that you should stick with a local equilibrium approach.

 

Try checking out Chapter 21 and 27 in the Geochemical and Biogeochemical Reaction Modeling textbook (and the references therein) for more info on Da and equilibrium vs. kinetics.

 

Regards,

Brian

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