Stefan Posted March 24, 2009 Share Posted March 24, 2009 Hello I have trouble keeping compatibility of thermodynamic data between datasets for different geochemical codes. Thus, I would like to know some details on the Pitzer formalism incorporated in GWB. Obviously, the Aphi parameter can be individually set for a specific dataset (and for the different temperatures herein) by the debye huckel a (adh) parameter. For the thermo_hmw dataset you take adh(25Â°C) = 0.5092. This corresponds with a value for Aphi of 0.3909 what when rounded is the value from Bradley and Pitzer 1979 (J. Phys. Chem 83/12) for 25Â°C and saturated pressure. In the original HMW 84 paper 0.39 was used. Looking in Archer & Wang 1990 ( J. Phys. Chem. Ref. Data 19/2) Aphi should be 0.39148. On page 351 in Craigs â€œgreen bookâ€ a value of 0.3920 is documented for calculating the Etheta values. Further, the values provided for Aphi in the thermo_hmw dataset agree with those of Bradley and Pitzer 1979 at 0, 25 and 60Â°C. At higher temperatures small deviations exist. Theses differences in Aphi (at 25Â°C and other temperatures) are small and thus leading to small differences in the resulting activity coefficients. For the application on â€œlarge scale real world problemsâ€ one can neglect this. But by trying to build a database with compatible thermodynamic values this makes the difference. Thus, I have two questions: 1) What is the value for Aphi used in GWB (or in different parts of GWB) for calculating activity coefficients following the Pitzer formalism? 2) What is the function behind the temperature dependency of Aphi in GWB datasets and - I assume - all other values listed in the same way for different temperatures? Best regards, Stefan Quote Link to comment Share on other sites More sharing options...
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.