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Fixing pressure for a batch geochemical model


Neda
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Hi Brian,

 

Could you please tell if GWB has the capability to simulate geochemical modelling at a fixed pressure. In the output files pressure is always set to 1.013 bars, while temperature can be set to any desired value. If changing the system pressure is not enabled in GWB, is there any trick to apply a fixed pressure in the batch models. Thanks for the reply.

 

Best,

Neda

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Hi Neda,

 

The pressure reported in the output file corresponds to the temperature you've set. This is because you can't currently set a confining pressure for your system*. All thermodynamic data in the datasets distributed with the GWB is compiled along the steam saturation curve. So you'll see a pressure of 1.013 bars up to 100 C, then the vapor pressure of water above that temperature. You can take a look at the Tables section of the thermo datasets to see the pressures corresponding to the principal temperatures.

 

If you'd like, you can compile a thermo dataset at a pressure or temperature of interest. See the K2GWB and DBCreate references on our thermo data page for more info. You cannot, however, set pressure independently like you can the temperature. For gases, as you've seen, you set the fugacity directly.

 

*You can set a confining pressure in Act2 and Tact, but not any of the other programs. This affects the positions of the water stability limits and the stability fields for gases, but does not affect the stability of species or minerals in the dataset. See 3.38, pressure, in the GWB Reference Manual for more info.

 

Best,

Brian

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