MTDATA – Phase Diagram Software from the National Physical Laboratory







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Calculation of pressure - temperature phase diagrams for a fixed composition

Typically this application might be used for calculating unary phase diagrams as a function of temperature and pressure. However the application is not limited to one component systems although, for multicomponent systems, some care must then be taken in interpreting the results of the calculations. After having loaded the appropriate data into MTDATA and selected the phase classifications as required, this application is initiated by entering "tp.mac". Prompts are provided to help the user to decide what to type in next.

The macro first provides a list of phases in the system and asks for the number of the phase which is stable at high temperatures (either the liquid or the gas phase). However if 0 is entered the application will not check for consistency.

Then the macro asks for the minimum pressure, the maximum pressure and the number of pressure steps to be used for the calculations. The application allow plots to be displayed either in terms of a linear scale in terms of pressure or as a log scale. There is a facility for searching for triple points but this is only possible when a one component system is under examination.

The macro also prompts for the maximum number of phase boundaries to be found. In order to find them all a relatively high number eg 20 should be entered.

Further prompts invite entry of the minimum temperature, the maximum temperature and the tolerance in termperature to be used for the calculation (for reasonable accuracy a value of 0.1 should be sufficient). Before it is possible to do a calculation, it is necessary to set the composition of the system. For a one component system this is, of course, straightforward. It is, however, also possible to carry out calculations on multicomponent systems eg for systems involving complex equilibria between a gas phase and various condensed phases.

The main output from this application is in terms of the calculated diagram which may be labelled interactively. However, if the calculations have involved a scan for triple points, tabular output may also be provided of the form:

Triple point found at :    0.5140E+10 Pa
                            1979.7 K

Triple point found at :    0.1046E+11 Pa
                             756.6 K

Pressure :    5.000000E+10 Pa


Updated 7 May 2010