Steam

In the case of steam/water flows, Autodesk Simulation CFD assumes a homogeneous two-phase mixture. The energy equation that is used is written in terms of enthalpy. Temperature is determined using the steam tables. Both temperature and enthalpy results can be viewed in the Results dialog task (make sure both quantities are enabled on the Output Quantity dialog on the Solve dialog).

Boundary Conditions

Specify the Steam Quality and static Temperature (as well as the appropriate velocity, flow-rate, or pressure) at all inlets. The steam quality is 0 for 100% liquid water.

Materials

Select the Steam (Saturated) material from the Fluid list on the Material dialog. If the operating state differs from STP, open the Material Environment dialog from the Material branch of the Design Study bar, and modify the Pressure and Temperature. The properties of the steam are determined during the analysis using the steam tables and the specified environment pressure.

Solve

• On the Physics tab of the Solve dialog, enable Heat Transfer.
• Click the Advanced button, and select Steam quality.
• For incompressible flows, only the temperature and reference pressure affect the fluid properties (including the steam quality).
• If local pressure effects are to be considered, enable Subsonic Compressible.

Steam Table Data

The Steam.dat file contains steam property information for saturated steam/water, superheated steam, and sub-cooled water. It is located in the top-level folder of your Autodesk Simulation CFD installation.

The file is divided into three sections, each corresponding to a different region of the steam-dome:

Saturated Steam/Water

Each line in the Saturated section contains the following data:

temperature	pressure	vapor enthalpy	liquid enthalpy	vapor volume	liquid volume
°F	PSI	BTU/lbm	BTU/lbm	lbm/ft³	lbm/ft³

Care should be used when solving for saturated steam due to the physically unstable nature of some steam flows, especially those in which phase change occurs.

Superheated Steam

For Superheated steam, multiple temperature data points are supplied at each pressure. Each line contains the following data:

temperature	vapor volume	vapor enthalpy
°F	lbm/ft³	BTU/lbm

Note that pressure data points are more concentrated below 80 psi than between 80 psi and the maximum supplied pressure. Because the distribution of pressure data is more coarse for higher pressures, steam results will tend to be more accurate for superheated steam at lower pressures.

If greater accuracy is needed above 80 psi, you can add additional data to the steam.dat file.

Sub-cooled Water

For Sub-cooled water, multiple temperature data points are supplied at each pressure. Each line contains the following data:

temperature	liquid volume	liquid enthalpy
°F	lbm/ft³	BTU/lbm

Reference

Van Wylen, G. J., Sonntag, R. E., Fundamentals of Classical Thermodynamics, 2nd edition, John Wiley and Sons, Inc., 1973