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[OLD] Act2/Tact question


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Subject: Act2/Tact question

From: Jennifer Houghton

We are noticing that whenever we try and run Act2 or Tact with a high temperature/pressure database (400 degrees, 500 bars) these two programs report steam saturation pressures on the plots even though the database is not set at steam saturation. Is this just a hardwired calculation that the program runs to report a pressure on the plot or is this actually the program rewriting the database? We would like to verify that the programs are using the log K's we specified in the database (500 bars) and not a calculated log K at steam saturation.

From: Craig Bethke

Subject: Re: Act2/Tact question

The pressure reported on Act2 and Tact plots is the confining pressure that you set with the “pressure" command. The default value is 1 atm below 100 C and the L-V curve at higher temperature. The programs use this value to determine positions of the water stability limits, and to set fugacities for any gases that may appear in the diagram. See Chapter 3 of the Users' Guide for more info. The GWB programs wouldn't dream of messing around with your thermo data. They use the log K's directly if you work at one of the principal temperatures in the thermo dataset, or figure values from polynomial fits to the log K's if you work at other temperatures. Nonetheless, since it's never a good idea to trust a computer program completely, you can quickly verify the position of any line on an Act2 or Tact diagram with by hand calculation or using Rxn.

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