MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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Thermotab

Introduction

provides output of the thermodynamic functions Cp, S, G, H, Phi = (G H)/T and Beta = G/RTln10, for temperatures specified by the user for pure substances and chemical reactions. The output can be produced in tabular or graphical form, and may be displayed on the screen or saved in a file. Graphical output can be sent to a local plotting device such as a laser printer.

To produce plots and tabulations, data for the substance(s) are retrieved from one or more databases and the appropriate calculations performed. The databases available will depend on the particular installation. They may include:

SGSUB   Pure substance database from Scientific Group Thermodata Europe (SGTE)
TPPS    Based on the publications of the Institute for High Temperatures (Moscow)
CSIRO   A database provided by the Commonwealth Scientific and Industrial Research Organisation, Australia (CSIRO)

Where there are several substances under consideration (for example, when a chemical equation has been entered), data for each substance may be retrieved from a different database, specified by the user. Facilities exist within the program for amending existing data and saving them into a user defined database: the reference databases supplied with MTDATA are protected against corruption.

Brief summary of commands

AUTOBALANCE The parameters set by AUTOBALANCE control the way in which an equation is automatically balanced. Note that the AUTOBALANCE command does not itself balance the equation balancing is invoked by DEFINE, USE or AMEND.

DEFINE allows the user to enter the SUBSTANCE formula or chemical EQUATION for which thermodynamic functions are required. If the entry is a chemical equation (including an equals sign), it is first balanced and then data for all substances present are retrieved from the default database.

STATUS displays the current status of parameters, such as the current equation and units, the default database, and the temperature and pressure lists.

USE_DATABASE searches a specified database in order to retrieve data for a named substance; it can also be used to change to another default database.

SET this command has two different purposes: (a)  it is used to specify one, or a series of temperatures for which thermodynamic functions are calculated and displayed by GO. (b)  it defines which thermodynamic functions are to be calculated and tabulated by GO.

STEP defines a series of temperatures for which thermodynamic functions are calculated and displayed by GO. STEP is a more convenient method then SET of specifying a series of more than three temperatures.

PLOT is used to define the variables to be plotted, and the labelling and scaling of the plot.

TABULATE controls the destination to which tabular output is sent when the GO command is issued. It also allows a title to be attached to the table.

AMEND allows the user to edit the equation or substance data.

SAVE_DATA incorporates data that has been assessed and amended by means of THERMOTAB into a database specified by the user.

LIST displays on the screen the thermodynamic data held in memory, as they have been retrieved from the database (and possibly amended).

QUANTIFY allows the user to alter the units of energy and temperature.

GO converts the thermodynamic data retrieved from the database into the thermodynamic functions specified in SET FORMAT and/or PLOT, and sends them to the terminal or file.

RETURN takes the user out of THERMOTAB back to the module level.

<"Macro name"> runs a macro taken from a file. The name of the file should be entered in quotes. Commands can also be passed through to the operating system by prefixing them with a $ (dollar sign). The dollar sign and operating system command should be entered within quotes.

Help facilities

The principles of the operation of the help system within MTDATA are given elsewhere. The purpose of the following is to draw attention to difficulties faced by users new to THERMOTAB. For the beginner nothing can be more frustrating than cryptic messages, which are difficult to interpret. This section provides two examples of situations in which, because THERMOTAB is not a human with chemical knowledge, the messages produced by THERMOTAB are not all they seem.

Example 1

THERMOTAB OPTION? define equation="H2" !
H2 NOT FOUND IN SGSUB

When substance(s) are entered using the DEFINE option, the default database is searched to retrieve the data. The NOT FOUND IN message means that the data are not present on the currently selected database in this case SGSUB. It seems strange that such a common substance is not on the database, until it is realised that the state of matter symbol has been omitted. The program will not point this out, because it takes an omission to indicate the default state . It does not know that hydrogen has rather a low boiling point.

Example 2

THERMOTAB OPTION? define equation="C" !
ADDITIONAL POSSIBLE PHASES FOR SUBSTANCE 1

When the substance is DEFINEd, the database is searched up to the point in the database where the entry is expected to be. During this process, if substances of the same phase, but different form, are found, they are displayed on the screen for information only. Data for these substances are not loaded into memory. If the DEFINEd substance is found, data for it are loaded into memory, but no confirmatory message is printed.

The ADDITIONAL SUBSTANCE message can be used to find out which forms of a particular substance in a given phase, are held on the database.

Further Information

A gentle introduction gentle introduction to using the options available in THERMOTAB contains annotated examples, each directed towards achieving a particular outcome, showing typical combination of commands which would be necessary to achieve that end.

A simple summary of the commands available can also be used as an index to obtain more detailed help about each command.

 

Updated 7 May 2010