bine Posted February 17, 2010 Posted February 17, 2010 Hello Tom, I have a question regarding the treatment of the Pitzer parameters alpha1 and alpha2 in GWB. In Craig`s book "Geochemical and Biogeochemical Reaction Modeling" (2nd edn) I find the following equation in Table 8.1 on page 125 (under step 4): BMX = beta0 + beta1 * g * (alpha1 * sqrt(I)) + beta2 * g * (12 * sqrt(I)) Is it correct, that the "12" represents the value of alpha2 and is it fixed to that value for every possible cation-anion pair? This would imply that the alpha2 values given in the parameter file are not really used? Thanks a lot for your help, Christiane Quote
Tom Meuzelaar Posted February 18, 2010 Posted February 18, 2010 Dear Christiane: The book uses a constant value because the parameter value is 12 for all cation-anion pairs (you can see this by inspecting the two Pitzer databases GWB uses, thermo_hmw.dat and thermo_phrqpitz.dat). The GWB code, however, picks up alpha_MX^(2) directly from the thermo dataset- so you can change these parameters to anything you want, and it will be reflected in the 2nd virial coefficient calculations. I hope that helps, Tom Quote
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