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Fluid evaporation using "React"


Penguin623
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Hi Brian,

 

I have modified "thermo_phrqpitz.dat" based on "thermo.dat", since I need Aluminum and Silicon to be added in the initial condition. In my calculation, I considered fluid evaporation and used "Flow-through configuration". However, after loading the modified database, the calculation gave me "Initial solution is too supersaturated". There is no further calculation. But, when I use "thermo.dat" to do the calculation, I could get a plot. Could you please let me know whether I can modify "thermo_phrqpitz.dat" and how? Or should I just use "thermo.dat" for fluid evaporation reaction path models if there is more element in my system?

 

I have attached the script and the modified database with this post. Please let me know your opinion.

 

Thank you very much!

thermo_phrqpitz_WXM.dat

Minerals-thermo.dat.rea

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Hi,

 

For this example, I would stick with the thermo.dat dataset. Your initial solution does not have a very high ionic strength and you are only evaporating about a third of the water. Running this example, the highest ionic strength reached is about 0.05 molal, so the B-dot equation (extended form of Debye-Huckel) works just fine. Thermo.dat also has the advantage of being parameterized from 0-300 C, unlike the phrqpitz dataset, which is defined at 25 C, though it has a limited (and largely untested) provision for calculations at other temperatures.

 

Unfortunately you cannot just add thermodynamic data for Al and Si to the phrqpitz dataset (which uses the virial activity model), without adding appropriate virial coefficients to the bottom section of the dataset. And if you are editing a database, be sure to follow the conventions outlined in the Appendix to the GWB Reference Manual. (Elements added in alphabetical order by name (Oxygen is always first, however), the list of Basis species must begin with H2O, etc.)

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions

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Hi Brian,

 

Thank you very much for your explanation, What iss the highest ionic strength the B-dot equation (extended form of Debye-Huckel) can accomodate? If the total water loss for my system is 50%, can I still use "thermo.dat"?

 

Thank you very much!

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From Craig Bethke's Geochemical and Biogeochemical Reaction Modeling text, Section 8.1.2:

 

"The B-dot equation...is considered reasonably accurate in predicting the activities of Na+ and Cl- ions to concentrations as large as several molal, and of other species to ionic strenghts up to about 0.3 to 1 molal."

 

You should take a look at Chapter 8 of that text, or Section 7.4 of the GWB Essentials Guide for more on the implementation of activity coefficients and activity models in GWB. As for your specific problem, I would use thermo.dat.

 

Hope this helps,

Brian

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