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Plotting

An advantage of using Excel is that it is very easy to make plots of your results. TPX comes with a workbook template which makes creating thermodynamic process representation plots even easier. In this section, we'll look at how to create plots using the template TPX_workbook.xlt first, and then how to do it in any workbook.

The TPX_workbook template

In the TPX folder is a folder labeled Templates, which contains the template file TPX_workbook.xlt. Open this file to create a new workbook based on the TPX_workbook template.

TIP: if you place the template TPX_workbook.xlt in the directory Program Files/Microsoft Office/Templates, then when you select New Office Document on the Start menu, or New... from within Excel, TPX_workbook will be one of the choices.

A workbook created with the TPX_workbook template has several chart sheets, labeled on the tabs on the bottom as shown below.
tabs.gif (1693 bytes)

Each of these sheets contains a blank process representation plot (T vs. S, etc.), showing the vapor dome in the current units. An additional sheet labeled Substance is present also. In order to plot the domes for the correct substance, you need to enter the substance name or formula where indicated on this sheet. The Substance sheet also lists the current units.

Making Plots

Suppose you have generated a table of properties such as shown below. This table of functions was made using the property calculator, and the column of labels on the left was added by hand.

prtab.gif (7261 bytes)

To plot this data, simply select the entire table, including the labels. Then right-click the mouse to pull up the pop-up menu, and select Add to Plots. This will cause all property pairs in the table [such as (P, h), or (h, s)] which correspond to one of the chart sheets in the workbook to be added to the appropriate chart.

View the P-H Plot
View the
T-S Plot

If the values in the input cells (blue) are changed, then the table recalculates and the plots automatically update. Once a plot is created, it can also be moved from its own sheet onto the current worksheet (as was done on the worksheet shown on the TPX Home Page).

Making plots without using the TPX_workbook template

Actually, what Add to Plots does is very simple, and can be used to create arbitrary plots - not just thermodynamic properties.

Add to Plots works only if a rectangular region is selected, with the  first column containing labels for the rows.

It loops through every pair of labels, and looks to see if there is a chart sheet which corresponds to those labels. If so, it adds a new data series to the chart which consists of the two rows from the table. Two rules must be followed for this to work:

1.     The row labels must consist of a single letter. (Note that in the table above, "rho" violates this, and thus this row will not be plotted.)

2.     The charts must be on separate sheets, each labeled "XY Plot", where "X" and "Y" are arbitrary letters.

For example, if you wish to plot  "a" vs. "q", simply create a chart sheet "aq Plot", a data table with an "a" row and a "q" row, and select Add to Plot.

In the next section, we will look at the TPX worksheet functions, and how to enter them directly into the worksheet.

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