Physical and Chemical Properties Division
National Institute of Standards and Technology
Boulder, Colorado
U.S. Department of Commerce
Technology Administration
National Institute of Standards and Technology
Standard Reference Data Program
Gaithersburg, Maryland 20899
The National Institute of Standards and Technology (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data contained therein have been selected on the basis of sound scientific judgment. However, NIST makes no warranties to that effect, and NIST shall not be liable for any damage that may result from errors or omissions in the Database.
Certain trade names and other commercial designations are used in this work for the purpose of clarity. In no case does such identification imply endorsement by the National Institute of Standards and Technology nor does it imply that the products or services so identified are necessarily the best available for the purpose.
Microsoft and Windows are registered trademarks of the Microsoft® Corporation; Lahey F77L and Lahey FORTRAN 90 are trademarks of Lahey Computer Systems®, Inc., Pentium is a trademark of Intel Corporation. Absoft ProFortran is a trademark of Absoft Corporation®. Digital Visual Fortran is a registered trademark of Digital Electronic Corporation®. Fortner Research Fortran is a registered trademark of Fortner Research Corporation®. Microsoft Fortran is a registered trademark of the Microsoft Corporatio.
©2000 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved. No part of this database may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the distributor.
Development of this database was supported by the NIST Standard Reference Data Program and the NIST Physical and Chemical Properties Division.
NIST Pure Fluids shares much of its code, and some fluids, with the NIST REFPROP database. The development of NIST REFPROP was supported by numerous sponsors including the Air-Conditioning and Refrigeration Technology Institute, the U.S. Department of Energy, the Electric Power Research Institute, the Environmental Protection Agency, Oak Ridge National Laboratory, the American Society of Heating Refrigerating and Air-Conditioning Engineers, the NIST Building Environment Division, the NIST Physical and Chemical Properties Division, and the NIST Standard Reference Data Program.
We gratefully acknowledge the development of the graphical user interface by Sandy Klein and the many helpful discussions with Richard Jacobsen, Roland Span, Marcia Huber, Arno Laesecke, and Richard Perkins. Finally we would like to acknowledge our many colleagues, too numerous to mention, whose property measurements and models we have taken from the literature; without this information, the database would be much reduced in scope.
1. INTRODUCTION
CONTENTS
1.1 Objectives and Scope of the Database
1.2 Uncertainties in Calculated Properties
1.3 Organization of the Users’ Guide
1.4 Reference
2. INSTALLATION
2.1 System Requirements
2.2 Installation
3. OVERVIEW
3.1 Database Structure
3.2 Use of the Database
3.3 Overview of the Menus
4. DEFINING THE FLUID OF INTEREST
4.1 Selecting a Pure Fluid
4.2 The Status Bar
4.2.1 Pure-fluid information screen
4.2.2 Changing property models
5. GENERATING PROPERTY TABLES
5.1 Calculating Saturation Tables
5.2 Calculating Iso-Property Tables
5.3 Calculating Tables at Specified State Points
5.3.1 Entering data into specified state point tables
5.3.2 Reading data into a table from a file
5.3.3 Using the specified state points table
5.4 Reformatting Existing Data Tables
5.5 Warnings and Errors
6. CREATING AND MODIFYING PLOTS
6.1 Plotting Data from Tables
6.2 Overlaying Data Onto Existing Plots
6.3 Predefined Plots
6.4 Modifying Plots
6.4.1 The Modify Plot command
6.4.2 Adding and deleting labels
6.4.3 Resizing and moving plots
6.4.4 Reading coordinates off a plot
7. CHANGING OPTIONS AND PREFERENCES
7.1 Units
7.2 Enthalpy and Entropy Reference States
7.3 Properties Calculated
7.4 Miscellaneous Preferences
7.5 Saving Current Options and Preferences
7.6 Retrieving Previously Defined Options
8. SAVING AND PRINTING
8.1 Saving and Closing Sessions
8.2 Retrieving a Previously Saved Session
8.3 Saving tables
8.4 Printing
9. IMPORTING AND EXPORTING DATA
9.1 Copying Data to the Clipboard
9.2 Pasting Data from the Clipboard
9.3 Deleting a Row of Data
10. MANIPULATING DATA TABLES AND PLOTS
10.1 Arranging Windows on the Screen
10.2 Retitling Windows
10.3 Going to a Window
11. THE ON-LINE HELP SYSTEM
12. USING THE DATABASE IN OTHER SOFTWARE AND HARDWARE
Appendix A: FLUIDS IN THE NIST PURE FLUIDS DATABASE
Appendix B: INFORMATION ON USING THE DATABASE WITH OTHER PROGRAMS
Appendix C: WARNING AND ERROR MESSAGES
Appendix D: SUPERFLUID HELIUM
Appendix E: CONTACTS
1.1 Objectives and Scope of the Database
Knowledge of fluid properties is essential for the evaluation of fluids for the application and design of equipment using fluids. The NIST Pure Fluids (also referred to as NIST12) computer database from the National Institute of Standards and Technology is one of the more widely used tools for providing data for the thermophysical properties of pure fluids. The standard property surfaces provided in this database are presented as thermodynamically consistent models, which can be used in such applications as custody transfer, calibrations, and innovation, design, and optimization of processes involving pure fluids. Although the recommended properties determined from the NIST Pure Fluids database should not be considered directly as legal standards for any purpose, such consensus standards and legal metrological standards in many technical areas are often tied to the NIST Pure Fluids computer database. Interested users should consult the relevant standards organization to determine the appropriate use of the NIST Pure Fluids database in these areas.
This fifth version of NIST Pure Fluids is a complete revision of the pure fluid database, and it is based on the most accurate pure fluid equations currently available. For each fluid, the recommended thermodynamic surface is represented by an empirical, multiparameter, classical equation of state based either on the modified Benedict-Webb-Rubin equation of state or on a more general type of Helmholtz energy equation of state. The viscosity and thermal conductivity are modeled with either fluid specific correlations or a new variation of the extended corresponding states model. Other properties, such as the dielectric constant, surface tension, and melting line, are calculated with fluid specific correlations. In the case of fluids for which the currently recommended property surfaces differ from previous versions of the NIST12 database, alternative properties, consistent with the older standard, can also be calculated from this version of the database.
A graphical user interface, designed for the Windows® operating system, provides a convenient means of accessing the models of NIST Pure Fluids. It generates tables and plots for any user-specified fluid. An on-line help system provides information on how to use the database. Information screens display fluid constants and documentation for the property models. Numerous options to customize the output are available as well as capabilities to copy and paste data to and from other applications.
These models are also accessible directly by users’programs, as they have
been implemented in a suite of FORTRAN subroutines that have been completely
rewritten from earlier versions of NIST12. They are written in a structured
format, are internally documented with extensive comments, and have been tested
on a variety of compilers. Routines are provided to calculate thermodynamic
and transport properties at a given (T,
)
state. Iterative routines provide saturation properties, including surface tension,
for a specified T or P state. Flash calculations describe single- or two-phase
states at specified state points, e.g., (P, h), (P, T), etc.
Information about the superfluid phase of liquid helium has not been incorporated in the graphical user interface. For those users requiring information about helium in the range of temperature from 0.8 K to the lambda (
) temperature (near 2.2 K), a separate executable program NIST12HE.EXE has been provided. Note that the content of NIST12HE is identical to that of Version 3.0 of the NIST12 database. Information about the NIST12HE program is given in Appendix D of this manua.
1.2 Uncertainties in Calculated Properties
Our objective in selecting property models for use in NIST Pure Fluids is to implement the most accurate models currently available, while ensuring consistent properties over an extended range of state variables. The user should be aware that the uncertainties in these models vary considerably depending on the fluid, property, and thermodynamic state. In general, the properties calculated from these models represent all of the best experimental data available to within experimental uncertainty. In turn, the quality of the measurements for any particular fluid, property, and region of the phase diagram reflects the accuracies required for commerce, design, calibration, and research. It is impossible to give simple, global statement of uncertainties, because even for the most well studied fluids with equations of state based on accurate and wide-ranging data, uncertainties are complicated functions of the temperature and pressure. In Version 5.0 of the NIST Pure Fluids database, general uncertainty statements (representing estimates of two-sigma combined standard uncertainties) are given in the fluid information screen for each fluid. The interested user is referred to the original literature sources for additional details. The fluid information screens, which include references to the literature and other key information, are described in Sections 4.2.1 and 4.2.2.
The user is further cautioned that in this calculational database, property data are computed and can be displayed with more digits than can be justified based on the accuracy of the property models or the uncertainties in the experimental data to which the models were fitted. The number of digits displayed can be adjusted by the user, as described in Section 5.4.
Many users will not need this guide for routine uses of the NIST Fluids database, as the procedures, layout, and commands have been designed to be both intuitive and similar to many other software products operating under the Windows operating system. This guide and the on-line help system can be used to provide additional information as required. Section 2 details the installation procedure. Section 3 presents an overview of the structure of the database and its main features. Sections 4 through 11 briefly describe the features of the database and Section 12 provides guidance for using these formulations in other software and hardware. The fluids in the database are tabulated in Appendix A. Use of the FORTRAN property subroutines is described in Appendix B. Appendix C discusses warnings and error messages generated by the property routines. Appendix D describes how to use the NIST12HE program to calculate the properties of superfluid helium. Appendix E lists support contacts at NIST.
NOTE: The figures in this manual show windows and dialogs as they appear in the Windows 95 operating environment. If you are in another environment, their appearance may be slightly different.
Friend, D.G. , NIST Standard Reference Database 12: NIST Thermophysical Properties of Pure Fluids, Version 3.0 , National Institute of Standards and Technology, Standard Reference Data Program, Gaithersburg.
NIST Pure Fluids is designed to run on any personal computer running the Microsoft Windows 95, 98, or NT operating system. The program requires 5.0 MB of hard disk space.
Put Disk 1 in the diskette drive (A or B). In Windows NT™, select File from the Program Manager’s Menu Bar followed by Run from the File Menu. In Windows 95, click on the Start button and select Run. In the command line box, type
and press enter. Follow the remainder of the installation instructions shown on the screen.
NIST Pure Fluids consists of a graphical user interface (GUI) and subroutines implementing a variety of fluid property models. The interface provides a convenient means to calculate and display thermodynamic and transport properties of pure fluids. The property models are written in FORTRAN and accessed by the GUI through a dynamic link library. The property subroutines can also be used independently of the GUI, as described in Appendix B.
The high-level subroutines that carry out iterative saturation and flash calculations are independent of the fluid property models. Underlying these subroutines are sets of core routines for each of the models implemented in the database. The numerical coefficients associated with the property models for each fluid are stored in separate text files. This structure simplifies the addition of new fluids and additional models to future versions of the database and makes such additions almost totally transparent to the user.
Start the NIST Pure Fluids database by double-clicking on its icon. A banner screen displays the title, credits, and a legal disclaimer. Clicking the "Information" button calls up further details and credits through the on-line help system. Clicking the "Continue" button starts the database.
The File menu provides commands to save and print generated tables and plots. Individual items or entire sessions with multiple windows can be saved and recalled. The standard Print, Print Setup, and Exit commands are included in this menu.
The Edit menu provides copy and paste commands, which allow selected data and plots to be exchanged with other applications.
The Options menu provides commands for selecting the units to be used for input and output, properties of interest, the reference state, and some user preferences. These options can be stored for later recall. A user-defined set of preferences is loaded upon program startup.
The pure fluid of interest is specified with commands in the Substance menu.
The Calculate menu initiates the calculations that generate a property table. Each property selected for display is shown in a separate column of the table. Two types of tables are provided. The first provides properties either at saturation or with a property (such as density or enthalpy) held constant and temperature or pressure varying over a specified range. The second allows the user to select the independent variables. Values of the independent variables can be entered with the keyboard, read from a file, or pasted from another application.
The Plot menu provides x-y plots of properties appearing in a table. In addition, simple temperature-entropy, temperature-enthalpy, and pressure-enthalpy diagrams can be generated automatically. Commands are provided to modify the plot size, axis scaling, plot symbols, line type, legend, and other plot features.
Each table and plot appears in a separate window and can be accessed, resized, or retitled with commands in the Window menu. The number of windows is limited only by available memory.
A complete online-help system can be accessed through the Help menu. A status line at the bottom of the screen displays the currently specified fluid and reference state. Clicking on the status line calls up information for the fluid, thereby providing documentation for fluid constants, the source of the models, uncertainties and the range of applicability.
4. DEFINING THE FLUID OF
INTEREST
(The Substance Menu)
The Substance menu defines the fluid for subsequent property calculations. Defining a new fluid has no effect on tables or plots already produced.
Selecting the Pure Fluid item in the Substance menu brings up the dialog box shown below. The available fluids are shown in a scrollable list on the left of the box alphabetized according to common name. (The fluids available in the database are also tabulated in Appendix A.) Select the fluid to be investigated by clicking the mouse button on the fluid name. An information screen of fluid constants (such as molecular weight and normal boiling point), reference information, and uncertainties is brought up by clicking on the Info button. The information screen is described in more detail in Section 4.2.1. The fluid name is displayed in the status bar at the bottom of the screen to confirm this choice.
A status bar at the bottom of the main window displays the fluid name and the reference state for enthalpy and entropy calculations (see Section 7.2).
If the settings for the front-most table or plot window displayed differ from the current settings, the information for that window is also displayed following the current settings information.
4.2.1 Pure-fluid information screen
Clicking the status bar or selecting the Fluid Information option under the Substance menu brings up an information screen.
The top border of the screen gives the short name for the fluid, its full chemical name (if different from the short name), and its Chemical Abstracts Service (CAS) registry number. The top portion of the information screen displays fluid constants-molar mass, triple point and normal boiling point temperatures, critical parameters, and acentric factor. These constants are displayed in units corresponding to the current set as specified in the Units dialog. Also displayed is the dipole moment; for those fluids with a temperature-dependent dipole moment, the value at the normal boiling point temperature is displayed.
The bottom portion of the info screen providesinformation on the models used to calculate the various properties. Information on the equation of state and the viscosity, thermal conductivity, and surface tension models can be called up by clicking on the tabs near the bottom of the screen. (The "equation of state" refers to a property model used to calculate all of the thermodynamic properties, including density, vapor pressure, enthalpy, entropy, heat capacity, and speed of sound.)
The temperature, pressure, and density ranges over which the selected model is applicable are displayed near the middle of the screen. Below that, a one-line description of the model is given. Finally, literature references and uncertainties are provided in a scroll box. The reference information can be copied to the Clipboard by highlighting the desired portions with the mouse and clicking the Copy button.
4.2.2 Changing property models
For many of the fluids, more than one model is available for some of the properties. If multiple models are available, the list box arrow to the right of the one-line model description is active; click this arrow to display the available models. The recommended model is identified with the term "NIST rec." Additional (alternative) models are identified with the term "Alt. model." Select the model to be used in subsequent calculations by clicking on its name. This option should be used with caution. In most cases, the NIST-recommended model should be used.
(The Calculate Menu)
The Calculate menu provides three options for generating tables of two distinct types. The Saturation Tables and Iso-Property Tables options calculate properties at even spacing of temperature, pressure, or quality at some fixed value of another property. The Specified State Points option allows arbitrary values of two or more variables to be entered in a variety of ways.
5.1
Calculating Saturation Tables
Selecting the Saturation Tables option in the Calculate menu brings up a dialog box from which the form of the table is specified. There are numerous options for saturation tables. Saturation tables display properties for the saturated liquid and saturated vapor, denoted by (L) and (V) in the table headings.
The type of table is specified by the left set of radio buttons. The independent variable is specified by the right set of buttons.
Clicking the OK button brings up a dialog in which the range and increment of the property to be varied and the value of the property to be held constant (if applicable) are entered. Default values are provided. The first time a table is calculated for a specific fluid, the defaults are based on the current units settings and the properties of the fluid. For subsequent calculations, the default values for the range and increment are those from the previous table. The range and increment revert to the fluid specific default values when a new fluid is specified.
While the calculations are in progress, a small window indicates the status. To stop the calculations, click the Cancel button. When the calculations are complete, a table displaying the results appears.
5.2 Calculating Iso-Property Tables
Selecting the Iso-Property tables option in the Calculate menu starts calculation of a table with one property held constant and either the temperature or pressure varied over a specified range. The following dialog allows the selection of the constant and varying properties. Click on one property from each list. Note that not all combinations are supported, and that the temperature or pressure button is dimmed for such cases.
Clicking the OK button brings up a dialog for specifying the value of the property held constant and the range and increment of the varying property. Default values are provided. The first time a table is calculated for a specific fluid, the defaults are based on the current units settings and the properties of the fluid. For subsequent calculations, the default range and increment are those from the previous table. The range and increment revert to the default values when a new fluid is specified.
While the calculations are in progress, a small window indicates the status; you can stop the calculations by clicking the Cancel button. When the calculations are complete, a table displaying the results appears.
5.3 Calculating Tables at Specified State Points
The Specified State Points option calculates properties at arbitrary values of two or more variables. The independent variables can be entered from the keyboard, read from a file, or posted from another application. Selecting this option from the Calculate menu brings up the following dialog.
Select the independent properties by clicking two check boxes at the top of the dialog. Note that some combinations are not supported, and these choices are dimmed when the first property is selected. Only two properties can be selected. If you want to change your selection, click a checked box to deselect a property before selecting another.
Select the mechanism for entering data into the table (as explained below). If the "Enter data manually" option is selected, enter the maximum number of rows in the table in the edit box to the right of this option. When the OK button is clicked, an empty table appears in which the independent variables are positioned in the leftmost columns. The words "Enter value" appear in table cells for which the independent variables have not been defined.
5.3.1 Entering data into specified state point tables
If the "Enter data manually" button is selected in the Specify State Points Table dialog, the values of the independent properties can be entered in three ways:
1. Values can be simply typed into the cells of the table. You can move to any cell by clicking the mouse in that cell, or move to adjacent cells by pressing the Tab or arrow keys.
2. Values can be pasted into cells from another application, such as a spreadsheet. Copy the values to the Clipboard using the Copy command in the other application. Then, in NIST Pure Fluids, click the mouse in the upper left cell in the table to highlight it and select the Paste command (under the Edit menu) to fill in the table.
3. Values can be automatically entered in a systematic way by clicking on the triangle marker at the upper right corner of the column header. This activates the Automatic Data Entry dialog. By default all rows in the table are affected by this command. Editing the row numbers(s) in the "First Row" and/or "Last Row" boxes at the upper left of this dialog can change specific rows. Note, however, that you cannot specify a row number greater than the maximum number of rows set in the Specify State Points Table dialog. Values in the table can be either set or cleared according to the radio button selected in the upper right. The value to be placed in the first row of the selected range must be specified in the "First Value" field. Below this is a second field that determines the other values in the table. These values can be specified in terms of an increment, multiplier, or final value, depending upon the selection made with the drop-down control.
A combination of data entry methods can also be used. For example, the Automatic Data Entry feature can be used to specify one of the independent variables while the others are keyed in manually.
5.3.2 Reading data into a table from a file
If the "Enter data from file" button is selected in the Specify State Points Table dialog, a standard file dialog appears. Use it to specify the file containing values for the independent properties. The Read Data File dialog appears. It displays the filename at the top of the dialog and the first 100 lines of the specified file in a scroll box just below the filename. The independent properties are listed in the bottom portion of the window; specify in which column of the data file each of the properties is located by clicking the up or down arrows to the right of the column number. The data must be arranged in columns separated by a tab, comma, or space. Any line starting with a non-numeric character is assumed to be a comment line and is skipped. Note that the units in the data file must be the same as the current settings, or nonsensical values may be calculated.
Clicking the check boxes at the left of the Read column and specifying the column number can also read one or more columns of "Userr data". Such data is placed in the rightmost column(s) of the subsequent table and may be any numeric data. Edit the words "User data" to change the column headings for these data. This feature is useful for comparing calculated properties with experimental values, for example.
5.3.3 Using the specified state points table
Once values for the independent variables are entered into a specified state point table (as described above), click the Calculate button at the upper left of the table to initiate the calculations. A progress bar appears, and the table is filled in when the calculations are complete.
Any of the independent variables can be edited once a table has been calculated; this causes the calculated values in the affected row(s) to be erased. Clicking the Calculate button refreshes the table. Note that only rows in which the independent variables have been edited are recalculated. You can have the program recompute the entire table by holding down the Ctrl key while clicking the Calculate button.
5.4
Reformatting Existing Data Tables
The property values are displayed in a default format in the calculated tables, which should be acceptable for most uses. The format of a column can be changed, or its position in the table shifted, by clicking on the column heading.
In addition to the default format, two other formats are accessible by clicking on the Style drop-down arrow (you have to click on the top of the column). The "Fixed decimal" style displays values with a fixed number of digits after the decimal place. The "Float decimal" style displays values in scientific notation with a fixed number of digits in the ordinate. If either of these styles is selected, an edit box appears below the style. Select the desired number of digits by typing the value in the edit box, or using the small up or down arrows to increase or decrease the displayed value. An example of the selected format is shown above the style drop-down box.
The user is cautioned that, by the very nature of a calculational database, property data are often displayed with more digits than can be justified based on the accuracy of the property models or the uncertainties in the experimental data to which the models were fitted. A large number of significant digits may be useful for the smooth plotting of results, the evaluation of numerical derivatives, or checking results with the original source.
The position of a column in the table can be changed by editing the value in the edit box at the bottom of the dialog. The number of digits can be changed for all columns and all currently displayed tables in the Preferences dialog under the Options menu; see Section 7.4.
It is not always possible to complete the requested property calculations. In such instances, the database returns a notation such as "not applicable" in a table cell, a warning message, or an error message.
Certain properties are not defined at states that are otherwise valid. For example, the viscosity and speed of sound are not defined for a two-phase state. The surface tension is not defined for single-phase states. In such cases the term "not defined" is displayed in the corresponding table cell(s), and the remaining properties are displayed normally. The quality can be defined in a variety of ways for subcooled liquid and superheated vapor states, and it is not defined for supercritical states. In these cases, the state (subcooled, superheated, or supercritical) is displayed in the table cell(s) for quality.
Warnings indicate a situation in which the calculated values may be suspect. The user is informed that one or more requested states has resulted in a warning by an Alert box, which is displayed after all calculations have been completed. The entire row in the table resulting in a warning is displayed in an italic font (even though the warning may arise from the calculation of a single property). You can view the warning message by clicking the affected row number(s).
Warnings are encountered when transport property values are requested at a temperature and/or pressure outside of the range of the model used for the calculations. The transport property models often have a more limited range than the corresponding thermodynamic property model; in these cases, the thermodynamic properties are calculated normally, but the transport properties generate a warning. Warnings are also issued when the temperature or pressure, or both, are above the stated limits of the equation of state, in which case the thermophysical properties have been extrapolated.
An error indicates a situation in which calculations are not possible. The error may be because of the failure of an iteration loop within the property routines to converge on a solution, but more commonly, is because states were requested for which calculations are impossible. For example, saturation calculations are not possible above the critical temperature. Also, while an equation of state can usually be extrapolated to slightly higher temperatures or pressures than the stated limits with good results, extrapolation to lower temperatures or higher densities can give nonsensical results and is not allowed.
When an error is generated by the property routines, an Alert box is immediately displayed giving the error message and the option to continue or cancel further calculations in the table. If the No button is clicked, any rows calculated before the error was encountered are displayed. If the Yes button is clicked, calculations continue (although further errors are likely), and a blank row will be seen in the table for any point(s) resulting in an error. The Yes to All buttons continues calculations, ignoring further, similar messages. A new Alert box will be displayed if a different error occurs.
6. CREATING AND MODIFYING
PLOTS
(The Plot Menu)
The NIST Pure Fluids database provides a plotting capability for all data appearing in a table. In addition, simple temperature-entropy, pressure-enthalpy, and temperature-enthalpy diagrams can be generated automatically. While these plotting capabilities help in the visualization of data trends and are adequate for many other purposes, the database is not intended to compete with programs devoted to plotting and data analysis. If you need to produce publication-quality plots, or carry out statistical analyses or other data manipulations, we recommend that you transfer the property data from NIST Pure Fluids to such a program. Section 9 of this manual describes the process to transfer data to other programs.
Once one or more property tables have been calculated, x-y plots can be generated by the New Plot command. The dialog shown below is divided into three blocks, which control the x-axis, the y-axis, and the source and appearance of the plotted data.
By default, it is assumed that data from the currently active table window are to be plotted. Other tables can be selected using the drop-down list at the upper right of the dialog. It is also assumed that all rows in the selected table are to be plotted. If this is not desired, the starting and ending row numbers can be entered in the edit boxes below the table list.
The variables to be plotted on the x- and y-axes are selected by clicking the column headings listed in the scroll boxes at the left and middle of the dialog. Appropriate minimum and maximum values for the plot frame are generated as the x- and y-variables are selected. The Interval value represents the spacing of axis labels. These values can be changed by typing new values; they can also be changed later using the Modify Plot command, which is described below. Two small drop-down boxes control the format of the axis labels. The first provides access to a fixed decimal format, "F", or exponential notation, "E". The second Format drop-down box controls the number of digits to be displayed after the decimal point in either format. Finally, the radio buttons at the bottom of the dialog can specify either a linear or logarithmic axis scaling.
The appearance of the plotted points is controlled by the commands in the lower right portion of the dialog. Points can be connected by a variety of line types, or no line at all, by selecting the desired option in the drop-down list labeled "Line." The "Symbol" drop-down list gives you access to a variety of plotting symbols, including no symbol. The color of both the line and symbol is also controlled by a drop-down list. Checking the "Smoothing" box fits a cubic spline through the data points to produce a smooth curve; otherwise plotted points are connected with straight line segments.
6.2 Overlaying Data Onto Existing Plots
You can plot additional data onto existing plots by using the Overlay Plot command. The command acts on the topmost plot window; if a different plot is desired, select it before executing the Overlay Plot command. This command brings up a dialog virtually identical to that for New Plot, which works in the same way, except that the plot limits are those of the existing plot and cannot be changed. (Plot limits can be changed later by the Modify Plot command; see Section 6.4.) If any of the new data are outside the range of the existing plot, you are prompted about rescaling the axes to accommodate all the data. It is the user’s responsibility to ensure that plots are not overlaid in meaningless combinations. In particular, the quantities in the individual data sets plotted should have the same units.
A number of often-used plots are predefined in the database and can be automatically generated for the currently defined fluid. Once plotted, these predefined plots can be modified, or additional data can be overlaid on them, in the same fashion as for any other plot.
A skeleton thermodynamic diagram on temperature-entropy coordinates is generated by the T-s diagram command. The saturated liquid and saturated vapor boundaries are always plotted. The dialog for this command allows specification of up to eight isobars (lines of constant pressure). Default values for four isobars are provided, which work well for most fluids. Entering the desired values into the edit boxes can change these. Isobars can be added or deleted by clicking the check boxes to the left of each isobar value. Each isobar is automatically labeled; these labels can be moved, resized, or modified as described in Section 6.4.2.
Clicking the OK button starts the calculations necessary to generate the diagram. If any errors are encountered in these calculations, an Alert box appears and informs you of the number of errors; it asks if you want to view the plot in spite of the errors.
The dialogs for pressure-enthalpy and temperature-enthalpy diagram commands are very similar to that for the temperature-entropy diagram described above. A check box near the bottom of the pressure-enthalpy dialog provides the option of plotting several lines of constant entropy in the vapor region.
6.4 Modifying Plots
6.4.1 The Modify Plot command
Many of the attributes of a plot can be changed through the Modify Plot command. This command can be accessed by the pull-down menu item or by double-clicking anywhere within an existing plot. In the former case, the plot in the foremost window is affected. If the foremost window is not a plot and there are multiple plots on the screen, a dialog appears from which the desired plot window can be selected.
The dialog for this command is similar to that used to specify a new plot, but has a number of differences. Options to modify the size of the axis labels and add gridlines to the plot are provided in the "x-axis" and "y-axis" portions of the dialog. As with the New Plot command, linear or logarithmic scaling can be selected, and the plot limits and axis label formats can be changed. The variables plotted cannot be changed, but the x- and y-axis labels can be edited.
A drop-down box in the upper right lists the ndividual data sets plotted. Selecting an item allows editing of the line and symbol attributes for that data set. The Delete button permanently deletes the selected data set. (Note that for the predefined T-s, P-h, and T-h plots, there is an entry for each of the lines in these diagrams.) Changes can only be made to one data set at a time. To change the attributes of multiple data sets, click the OK button and re-enter the Modify Plot dialog.
6.4.2 Adding and deleting labels
The Add Label command places text in a plot window. A plot must be in the foremost window for this command to be active. Invoking this command brings up a dialog in which you can type the desired text. Other text characteristics including the font, size, color, and orientation can also be edited. The "Opaque background" option is invoked by a check box; when this option is turned on, any lines "underneath" a text label are blocked out.
You can modify an existing label (including those generated through the predefined T-s, P-h, and T-h diagrams options) by double-clicking within the boundaries of the text. (A single mouse click reveals the text boundaries.) A label can be permanently deleted with the Delete button.
Clicking within the text boundaries and dragging the text to its new location can move labels.
6.4.3 Resizing and moving plots
The size of the plot frame can be changed. Place the cursor over the lower right corner of the plot; the cursor changes to a four-headed arrow to indicate that you are in the resize mode. Click and hold the mouse button while dragging the corner of the plot to enlarge or reduce the plot size.
To move a plot, place the cursor anywhere in the plot frame (except the resize box at the lower right); click and hold the mouse button while dragging the plot to its new location.
6.4.4 Reading coordinates off a plot
You can display the (x, y) coordinates of any point within the plot frame. Press and release the Shift key to display cross hairs within the plot frame and numerical coordinates (in units corresponding to the plot axes) in the title bar of the plot window. Use the mouse to move the cross hairs to any desired point in the plot. Toggle this mode by pressing the Shift key again. The Shift key can also be held down continuously to activate this mode, but the cross hairs do not appear until the mouse is moved.
Note that the cursor is "trapped" within the plot frame when this mode is activated. Press the Shift key to regain normal control of the cursor.
7. CHANGING OPTIONS AND PREFERENCES
(The Options Menu)
Under the Options menu, you can choose the units of measure for the calculations, the reference state for enthalpy and entropy, the properties to be displayed, and other options. All of these options can be saved (together with the currently defined fluid) for use in a future session. Any changes in these options apply to all subsequent tables but do not affect any existing tables (with one exception, as explained below).
The Units command brings up a dialog in which the units of the various properties can be specified. The current settings are displayed down the left side of the dialog window.
Click the SI or English buttons to set all of the units to one of these unit systems. Units can also be set individually-click on the arrow to the right of the current unit setting. A drop-down list of available choices appears. Click the desired unit. Specific properties (i.e., those expressed in terms of a unit quantity) are reported on either a mass or molar basis (e.g., kJ/kg or J/mol). Select the desired basis by the radio buttons under the heading "Specific Properties." The size of the molar and mass bases is governed by the selection in the Mass list box and is selected together. For example, selecting "kg; kmol" specifies kilograms if the mass basis is selected and a kilomole (often called a "kilogram mole") for the molar basis; selecting the English units "lb; lb mol" specifies pounds and pound moles. Some properties use combinations of the displayed settings. For example, if kelvins, kilograms, and kilojoules are specified for temperature, mass, and energy, respectively, entropy is displayed in units of kJ/(kg-K).
7.2 Enthalpy and Entropy Reference States
The properties of enthalpy and entropy are computed as differences relative to some arbitrary reference state. The Reference command allows the selection of one of the following reference states:
1. The "normal boiling point" (NBP) choice sets the enthalpy and entropy to zero for saturated liquid at the normal boiling point temperature.
2. The choice of zero for enthalpy and entropy for the saturated liquid at -40°C (-40°F) corresponds to the reference state traditionally used for refrigerants in the United States, including the tabulations of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
3. The International Institute of Refrigeration (IIR) has adopted reference state values of 200 kJ/kg and 1 kJ/(kg-K) for enthalpy and entropy, respectively, for the saturated liquid at 0°C. ASHRAE also uses this reference state for most refrigerants in its tables in SI units.
A user-specified reference state can also be selected. If that radio button is selected, the four edit boxes underneath it become active. Enter the desired values of enthalpy (h) and entropy (s) at the reference state temperature (T) and pressure (P) into the edit boxes.
All of the above reference states may not be applicable to a given fluid. For example, the IIR and ASHRAE reference states specify a reference temperature above the critical temperature for some fluids. A default reference state is stored in the data file for each fluid. This reference state will be read from the file and applied if the choice "Use the default reference state of the fluid file" is selected.
The properties to be displayed in calculated tables are controlled by the Properties dialog. Select or deselect any property by clicking the check box next to its name.
The Preferences item in the Options menu brings up a dialog to specify the behavior of the database in a number of aspects. Clicking on the check box next to the item "Copy table headers to clipboard with table data" places the text in the column headers on the Clipboard along with the table data when the Copy Table Data command is executed from the Edit menu. The column headers consist of the properties and units and are placed on two lines. This item should be disabled if data are pasted into a Selected State Points table within the NIST Pure Fluids database.
The database can be set to display prompts to save tables and plots when closing a session or the application. This reminder can be enabled or disabled by selecting or deselecting the second preferences item.
A third option determines if the saturation boundary is displayed during the calculation of an isobar or isotherm. If the option has been selected, the properties at saturation are included in the isobar or isotherm table with a line between the liquid and vapor phase.
The fourth option enables the Enter key to be used in the same manner as clicking on the "Calc" button when entering state points as described in Section 5.3.
The final option in the Preferences dialog specifies the number of digits displayed as default for all columns of all subsequent tables. This is a shortcut to the normal way of changing the data format by clicking on the heading of each column as described in Section 5.4. The option can be applied to all existing tables by clicking the check box underneath the box specifying the number of digits.
7.5 Saving Current Options and Preferences
The current settings can be saved at any time for recall. The settings saved include the currently defined fluid, units of measure, the reference state for enthalpy and entropy, the properties to be displayed, and the options specified in the Preferences dialog. Selecting the Save Current Options command brings up a file save dialog to specify the filename to contain the current settings. Settings files are identified with the ".prf" file name extension. Multiple settings files can be saved corresponding to different projects, etc.
The database reads the settings file "defaults.prf" at startup. To have the current options used as the default settings, save them in the "defaults.prf" file. An Alert box shows if the file already exists and asks if the existing file is to be replaced. Click the Yes button to save the new defaults.
WARNING: Do not delete the "defaults.prf" file. This file is needed to start the program, and if it is missing, the program will not run. If the "defaults.prf" file is inadvertently deleted, rename another settings file to "defaults.prf" and place it in the same directory as the NIST12 executable. The program can then be restarted. Check and, if necessary, change all the settings.
7.6 Retrieving Previously Defined Options
Any previously stored settings can be loaded by executing the Retrieve Options command. This brings up a File Open dialog. The settings files are identified by a ".prf" filename extension. Select the name of the desired settings file an click OK to load those previously defined settings including the fluid or mixture, units of measure, the reference state for enthalpy and entropy, the properties to be displayed, and the options specified in the Preferences dialog.
(The File Menu)
8.1 Saving and Closing Sessions
A session in the NIST Pure Fluids database comprises all table and plot windows on the screen together with the settings defining the fluid, unit system, reference state, and selected properties used to generate those windows. A session can be saved at any time, meaning that the complete current state of the program is saved to disk. The Save Session command brings up a File dialog. Select the desired directory and enter a filename; the ".rfp" file-type extension identifies a file as a NIST Pure Fluids session file to the database.
The Close Session command closes all table and plot windows currently on the screen, but the database itself remains running. If the session is not already saved, a dialog asks to save the current session before closing (unless this reminder has been disabled under the "Preferences" dialog).
8.2 Retrieving a Previously Saved Session
A previously saved session can be retrieved by the Open Session command. This command, combined with Save Session, is a very powerful combination that allows the user to stop work on a NIST Pure Fluids analysis and then return to it later or work simultaneously on several different analyses.
The Open Session command brings up a File dialog to specify the file storing the desired session. This command is active only if no table or plot windows are currently displayed. Upon pressing the OK button, the specified session is restored with all of its constituent table and plot windows on the screen. The settings defining the fluid, unit system, reference state, and selected properties used to generate those windows are also restored.
Individual data tables can also be saved. The Save Tables command displays a dialog to select one or more of the current tables to be saved to disk in an ASCII format. The available tables are shown in the list at the left. Click on the name of the table to be saved and then click on the ">" button to add that table to the list of tables to be saved on the right. The ">>" button moves all of the available tables to the right list. Remove a table from the "to be saved" list by highlighting its name and pressing the "<" button. Similarly, all of the tables can be removed by pressing the "<<" button. Alternately, tables can be moved by clicking on their names and dragging to the desired list.
The check box at the lower right gives the option to include the column heading (consisting of the property and units on separate lines) together with the data. An exponential format is used for all data. A delimiter selected by the radio buttons at the lower right is placed between each value in a row; a carriage return is placed at the end of the row. Most spreadsheet programs use the tab character to place items in separate cells. Multiple tables, if specified, are saved to a single file.
The Print Setup command brings up a Print Setup dialog that gives access to print options, such as landscape or portrait format and printer selection. These options are applied to subsequent output from the Print command. This command need only be used when the default printer or printer options are to be viewed or changed.
The Print command allows any of the tables or plots to be printed. The available windows are shown in the list at the left. Click the name of the table or plot to be printed and then click the ">" button to add that window to the list on the right. The ">>" button moves all of the available windows to the right list. An item can be removed from the "print" list by highlighting its name and pressing the "<" button. Similarly all of the tables and plots can be removed by pressing the "<<" button. Alternately, items can be moved by clicking their names and dragging to the desired list. Clicking OK initiates the print process; a small window with the message "Printing in progress" may appear.
9. IMPORTING AND EXPORTING DATA
(The Edit Menu)
9.1 Copying Data to the Clipboard
The Copy commands can be used to copy a plot or selected data from an existing window to the Clipboard. (The Clipboard is an area of memory used to exchange data within and between applications.) It can then be pasted into another application, such as a word processor or spreadsheet. When a plot is the foremost window, the menu item appears as Copy Plot; for a table it appears as Copy Table Data.
To copy a plot, bring the desired window to the front by clicking on it or by selecting its name under the Windows menu. Then select the Copy Plot command. The plot is placed on the Clipboard as a bitmap graphic, which can be pasted into most applications.
To copy data, it is first necessary to select the cells to be copied. To select a block of data, click the cell at one corner of the block, then press Shift and click at the diagonally opposite corner of the block. You can also select a block by dragging the mouse over it while depressing the Shift key. You can also select the entire table by choosing Select All command under the Edit menu.
Once a block of data is selected, executing the Copy Table Data command copies it to the Clipboard. The table headings may also be copied along with the data, depending on the setting in the Preferences dialog (see Section 7.4). If you intend to Paste the selected data into another NIST Pure Fluids table (such as a specified state points table), the "Copy table headers" preference should be turned off.
The Save Tables command provides another way to exchange data with other applications; see Section 8.3.
9.2 Pasting Data from the Clipboard
The Paste command places the contents of the Clipboard into the currently active input cell or edit box. This capability can be used to copy individual items, but is most useful in filling in the independent variables in a "Specified State Points" table. To paste data into such a table, first click the top-left cell of the block into which the data are to be placed in the Clipboard, then choose Paste from the Edit menu. The tab character must separate entries in the same row and a carriage return character must be used to delineate rows. If pasting non-numerical data into a table is attempted, an Alert box displays "Bad number in row xx column yy." This alert will be encountered if table headings were copied to the Clipboard along with the data. Turn off the "Copy table headers" preference to avoid this (see Section 7.4).
The Delete Row command allows a specified row to be permanently removed from a data table. This command is active only if a table is the topmost window. A dialog asks for the row to be deleted.
10. MANIPULATING DATA TABLES AND PLOTS
(The Window Menu)
Each table or plot appears in a separate window and can be accessed, rearranged, or retitled with commands in the Window menu, which work in the manner of most other Windows applications. The Window menu contains the three permanent options Tile, Cascade, and Retitle. An additional menu item is provided for each table or plot window on the screen. The number of windows is limited only by available memory.
10.1 Arranging Windows on the Screen
The Tile command resizes and repositions the existing windows so that all are displayed. The Cascade command overlaps all of the existing windows so that their title bars are visible, making it easy to select any of the windows. In addition to the Tile and Cascade commands, windows can be rearranged in the usual fashion by clicking and dragging on the title bar.
Each table and plot is provided with a default title when it is generated. These titles are used to identify the windows acted upon in the Save Tables, Print, New Plot, and Overlay Plot commands. The title of any window can be changed by first clicking anywhere in the window or clicking its title under the Window menu (to make it the active window) and then clicking on the Retitle command. A dialog box appears listing the current title with an edit box where a new title can be entered.
Any window on the screen can be brought to the front and made the active or default window by clicking anywhere in the window. Alternately, you can click its title under the Window menu.
(The Help Menu)
On-line help is available under the Help menu. The help system used in NIST Pure Fluids is a standard implementation and works in the manner of most other Windows applications. Instructions for using the help system are available through the Using Help command.
The Help Index command brings up a listing of the main topics in the help system. Click on the item for additional information. Help can also be accessed from most individual dialog boxes. Pressing the F1 key opens the help system at the point containing instructions for the use of that dialog.
A search capability is available by pressing the Search button. The previous topic is recalled by pressing the Back button. The History button (which is accessed from the Help Options menu) lists, and gives access to the last several help topics viewed.
The About NIST Pure Fluids command brings up the banner that is displayed on the opening screen.
12. USING THE DATABASE IN
OTHER SOFTWARE AND HARDWARE
The thermophysical property formulations of the NIST Pure Fluids database can be used directly within the users' computer code in order to adhere to these standards within other software applications, in hardware control applications, etc. Any such use must be in compliance with the users' license agreement; please contact the Standard Reference Data Program as indicated in Appendix E if there are any questions regarding this issue.
The most straightforward method of incorporating these standards involves linking the users' program with the FORTRAN subroutines, which can be obtained as part of the NIST Pure Fluids database. The code in the subroutines has been well documented with comments in order to make this integration as easy as possible. The user is urged to be extremely cautious about making changes within any of the NIST Pure Fluids subroutines; there should be no reason to change any of the core subroutines or fluid data files. With any use of the NIST Pure Fluids standards within a user application, it is necessary for the user to conduct sufficient tests to ensure that the fluid properties have not been altered. Information about the required FORTRAN subroutines and linking procedures is provided in Appendix B. The comments and code within the source files can be reviewed for further information.
If you have comments or questions about the database, the Standard Reference Data Program would like to hear from you. Also, if you should have any problems with the diskettes or installation, please let us know by contacting:
If you have technical questions or problems pertaining to the data, contact:
http://www.nist.gov/srd/nist12.htm
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