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Influence of element's order in Basis?

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Dear Forum members,

recently I tried to model a seawater evaporation and I ended up with different results (using the same Pitzer database) with the identical .rea-files input just with different order of entries n(concerning the species in Basis) in the two files. One file I had created in my own in React (Working_example.rea), the other one (Aborting_example.rea) was created by launching React from GSS. The chemical composition is the same in both files but the one from the GSS-launched React instance stops much earlier.

I would like to understand the different behavior, in principle, it shouldn't do that.

Thank you in advance and best regards,








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Hi Frank,

Evaporation problems become extremely difficult as the solvent mass approaches 0. Even the working example “fails” before reaching the end of the simulation. This is noted in the evaporation examples in the GBRM textbook and the GWB Reaction Modeling Guide. Eventually a lot of really small numbers (some positive, some negative) are added together, and the net result is a really, really small number. In cases like this the order in which the numbers are added, which reflects the order of the species in the basis, can make a difference. Mathematically it’s a little head-scratching, but it’s a real computer science issue. 

Keep in mind that you’re plotting the results in terms of solvent water remaining on a log scale, so it appears the aborting examples fails much, much earlier than the working example. The two examples yield essentially identical output until the aborting example fails after reaching a Xi value (Xi ranges from 0 to 1 over the course of a simulation) of .9857. The “working” example continues slightly further before failing at Xi = .9987. 

Hope this helps,

Brian Farrell
Aqueous Solutions LLC

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  • 2 weeks later...

Hi Brian,

thank you very much for your comment! ?

Best regards,


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