This example demonstrates the use of the NIST/ASME Steam Properties database to compute and plot the vapor pressure and fugacity at saturation (in units of bars) as a function of temperature. The temperature range is 100 to 350 °C.
To start in Windows 98, Windows 95 or Windows NT, either DOUBLE-CLICKon the STEAM icon or the Windows Explorer to go to the application and DOUBLE-CLICK on it. Another way to start the database is to go to the Start button and choose the database under the Programs option.
First, choose the Units item from the Options menu. CLICK on the Temperature drop-down list box and choose C. (In this appendix, italics indicate the button to be clicked on or the selection to be made.)CLICK on the Pressure drop-down list box and choose bar.CLICK OK. Now any calculations you make are displayed in those units.
Next, choose Saturation Tables from the Calculate menu. The resulting dialog box is used to specify the type of saturation calculation. Because the default selection is vapor-liquid saturation at specified temperatures, simply CLICK OK. The next window is for entering the set of conditions for the calculations (in this case, the series of temperatures for which property data are desired.) Enter 100 for the initial temperature and 350 for the final temperature. Change the increment to 10 degrees. CLICK OK. The database performs calculations and produces a table, the initially visible portion of which is shown in Figure A-1.
Figure A-1. Table produced in sample session.
It is possible either to begin plotting immediately or to examine and revise the table. In this example, we want to change the format of the table so that the fugacity is displayed next to the pressure. This involves moving column 20 (fugacity) to column 3. Scroll the table over to the fugacity column and CLICK in the header at the top of the column. Change the setting of the “Move to column” item from 20 to 3, and CLICKOK. Scroll the table back to the beginning, and note that the fugacity is now in column 3. The visible portion of the table now looks like Figure A-2.
Figure A-2. Table produced in sample session after rearrangement of columns.
To begin plotting,select New Plot from the Plot menu. By default, the Temperature column is selected as the X-axis and the Pressure column as the Y-axis. The other settings are also appropriate, so CLICK OK. The result is a plot of pressure as a function of temperature. To plot the fugacity on the same graph, select Overlay Plot from the Plot menu. Keep temperature as the X-axis and choose fugacity as the Y-axis. To distinguish the two graphs more easily, choose the solid circle from the Symbol drop-down list. CLICK OK. The resulting plot has two superimposed graphs. Note that (because of roundoff) the X-axis has been scaled from 50 to 350 rather than 100 to 350. To fix this, DOUBLE-CLICKon the plot to reach the Modify Plot dialog box. Go to the X-axis section and change the Minimum entry to 100. CLICK OK. The final plot should appear as shown in Figure A-3.
Figure A-3. Plot produced in sample session.
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