Thermodynamic Content

Steady-state mass and energy balances on the throttle are used to evaluate the downstream enthalpy, temperature, and velocity. Kinetic energy terms, often excluded when doing such problems by hand, are included in this analysis. Depending on the upstream and downstream pressures, the calculated velocity at the exit can exceed the local speed of sound. If this situation occurs, a message will be displayed. The calculated temperature is incorrect in this case.

EES features

This example illustrates several capabilities of the Diagram window. Graphical objects can be placed in the Diagram window, resized, and moved about when the Diagram window is in Development mode. To enter or exit Development mode, select Diagram from the Windows menu or enter Ctrl-D. The graphical objects can be drawn within EES using tools on the toolbar that is visible in Development mode or they can be created in another application and pasted into the Diagram window using the Paste command in the Edit menu. In this example, the throttle body was drawn in PowerPoint and pasted.

Text can be placed on the Diagram window using the text tool in the Diagram window tool bar. The text can be static, or it can be used for input and output of EES variables. Input variables are displayed within an edit box that invites the user to enter a value. The characteristics (size, font, color, style, angle) of any text item can be changed by right-clicking on the text item in Development mode.

A Calculate button can be placed on the Diagram using the toolbar button at the upper right of the toolbar. The Calculate button can be dragged to the desired location. Right-clicking on the Calculate button while in Development mode will bring up a dialog that allows the button size, title, location, and function (Solve, Solve Table, Min/Max, etc.) to be specified. The button can also be dragged to the desired location.

If the calculated exit velocity exceeds the local speed of sound, a warning message is displayed; the warning message is otherwise hidden. EES provides the capability to control the characteristics of text and graphic items in the Diagram window. To provide this capability, it is necessary to assign a name to the text item. The name AboveSoundSpeed was assigned in the dialog that appears after right-clicking on the text item in Development mode. Once the name is assigned, attributes such as color, size, position, etc. can be controlled with EES variables. Note that AboveSoundSpeed.Hide is set in Function Check in the Equations window.

The Professional version of EES allows a "live" plot to be placed within the Diagram window. Once this is done, the plot can be viewed in any version of EES including a Distributable program that can be generated by the Professional version. The first step is to generate the plot in a Plot window. If the plot is to be live, the Automatic Update button should be checked. To place the plot in the Diagram window, select the "Add Plot" button on the Diagram window toolbar (2nd from top on the right) and choose the desired plot. The plot can be dragged to the desired location and resized in Development mode. The plot will display exactly the same information that is seen in the Plot window. Child Diagram windows are provided in the Professional version. The Plot can also be displayed in a Child Diagram window.