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Geochemist's Workbench Support Forum
Misato Shimbashi

Change nucleus density in X1t

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Hi.

I have question about change of nucleus density with time in X1t.

I would like to set nucleus density of a precipitates 10 [cm2/cm3] before 3000000 seconds.

After 3000000 seconds, I would like to set nucleus density this equation: 10*(1/2)^((Time-3e6)/150000) [cm2/cm3]

How can I make it ? 

Screen shot of the reactants field is attached.

Thank you.

gwb.pptx

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Dear Misato,

I would recommend using the ‘script’ or ‘script file’ option for setting the nucleus density rather than an ‘equation’. Using a script or script file would allow you to set 10 [cm2/cm3] if Time is less than 3000000 seconds and after that, the equation desired.

It would look something like this:

IF Time < 3000000 THEN 20 ELSE 40
20: nucleus = 10
GOTO 60
40: nucleus = 10*(1/2)^((Time-3e6)/150000)
60: RETURN nucleus

As you’ve done, you need to check the “transient” option to evaluate the variable at each time step. Please refer to section 5.2 of the GWB Reaction Modeling Guide and the Heterogeneity Appendix to the GWB Reactive Transport Modeling Guide for more information.

Please note that the nucleus density option prescribes a minimum value for a supersaturated mineral’s surface area over the calculation. The program calculates the actual surface area from the mineral’s current mass and specific surface area and uses this whenever it exceeds the nucleus density.
 

Best,

Jia Wang

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