pe unexpected values

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8 months 1 week ago #325 by AhmedHussain
Recently I have started using iCP, and I started off with 'Example 2 Temperature Coupling', because it is closest to my situation. In my results I see that the pe has values which I cannot explain, probably due to a mistake I made somewhere, but not sure where.

Summary of my case:
-based on ex. 2, (but I simplified to 2D)
-inject water into a porous medium. Injection water has the same composition and T as water in porous medium
-no reactions take place and pH is constant in porous medium (as expected)
-pe is nonuniform (between -2 and 7!)

Could you please help me with understanding where I made a mistake?
I attached the PHREEQC, COMSOL and iCP files.

Thanks in advance,
Ahmed
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8 months 1 week ago #326 by ecoene
Replied by ecoene on topic pe unexpected values
Dear Ahmed,

I do not think there is a mistake with your implementation of iCP. The problem is rather with your conceptual PhreeqC model. Your PhreeqC model consists of a simple MgCl solution in which there is no redox pair controlling redox potential. As a result, small numerical errors in Comsol result in large pe variations.
In Example 1 of the PhreeqC manual you can see how to control pe with a given redox pair, in this case oxygen:

SOLUTION 1 SEAWATER FROM NORDSTROM AND OTHERS (1979)
units ppm
pH 8.22
pe 8.451
density 1.023
temp 25.0
redox O(0)/O(-2)
Ca 412.3
Mg 1291.8
Na 10768.0
K 399.1
Fe 0.002
Mn 0.0002 pe
Si 4.28
Cl 19353.0
Alkalinity 141.682 as HCO3
S(6) 2712.0
N(5) 0.29 gfw 62.0
N(-3) 0.03 as NH4
U 3.3 ppb N(5)/N(-3)
O(0) 1.0 O2(g) -0.7

I hope this helps!

Best regards,

Emilie
The following user(s) said Thank You: AhmedHussain

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