Thermodynamic Properties Phase Diagrams: Interactive Simulations

The first two simulations were prepared using Mathematica. Download the free Wolfram player, and then download the simulation CDF file (link given below or click on figure to download). The third simulation will run in your browser. Try to predict the behavior when a parameter changes before using a slider to change that parameter. Screencasts below explain how to use most of these simulations.

This demonstration shows a pressure-enthalpy (P-H) diagram for water. Check and uncheck the boxes to add or remove a property from the diagram. You can show lines of constant vapor quality (mass % vapor, blue), temperature (green), density (orange, dashed), and entropy (purple, dashed). Check the “critical” box to view the saturated liquid (light blue) and saturated vapor (red) curves and the critical isotherm (pink).

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

  1. At low pressures and high enthalpies, how does enthalpy change with pressure? Why?
  2. At low enthalpies and relatively high pressures, how does enthalpy change with pressure? Why?
  3. At a low, constant quality, how does the enthalpy change as temperature increases?

This demonstration shows a temperature-entropy (T-S) diagram for water. Use the checkboxes to add or remove a property from the diagram. You can show lines of constant enthalpy (green), pressure (blue), and quality (mass % vapor, purple). Check “phase envelope” to view the saturated liquid (magenta) and saturated vapor (orange) curves and the location of the critical point.

Try to answer this question before determining the answer with the simulation. We suggest that you write down the reasons for your answer.

  1. In the vapor region on a temperature-entropy diagram, as the temperature increases at constant entropy, what changes and how?
Simulation: Pressure-Volume Diagram for Water

This simulation helps you learn how to read pressure-volume diagrams. This diagram contains constant enthalpy, entropy, temperature, and quality lines in every phase (gas, liquid, solid). You can toggle each property on or off to make the diagram easier to read. It also helps you understand water behavior in the 2-phase region, because the diagram contains a phase envelope.

Try to answer this question before determining the answer with the simulation. We suggest that you write down the reasons for your answer.

  1. A fixed-volume container has 9 kg of liquid water and 1 kg of water vapor at 0.10-MPa pressure. The pressure and temperature increase. Does the entropy increase, decrease, or not change?

This demonstration shows a enthalpy-entropy (H-S) diagram for water. Use the checkboxes to display lines of constant pressure (purple), temperature (green) or vapor quality (mass% vapor, blue). Check “phase envelope” to show saturated liquid (magenta) and saturated vapor (orange) curves and the critical point (black dot).

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

  1. Locate the critical point on the phase envelope on the enthalpy-entropy diagram.
  2. In the phase envelope, why are the constant pressure lines parallel to the constant temperature lines?