The following topics will be discussed:
The Basic Settings tab is used to set the type of material, its state, an optional description and an optional coordinate frame.
Set the Material Group.
For details, see Material Group.
The Material Description field is optional.
For details, see Material Description.
Select the Thermodynamic State.
For details, see Thermodynamic State.
Optionally set a custom coordinate frame for any material properties that depend on expressions in X, Y, or Z.
For details, see Coordinate Frame, Coordinate Frames, and Coordinate Frames in the CFX-Solver Modeling Guide.
There are two main categories specifying properties of a pure
substance: General Material and Table. A General Material can have its thermodynamic,
transport and radiation properties defined in the most general manner
using any of the built-in flow solver models, constants, or CEL expressions.
A table material uses an RGP file to look up the required
values. For details, see Table.
General Materials can have their Equation of State set to the following options:
For details on equations of state, see Equation of State in the CFX-Solver Modeling Guide.
The following tab appears when Equation of State is set to Value. Value uses whichever model for density that is supplied by the user. For
example, the equation of state model could be a constant or a CEL
expression.
Equation of State > Option. For details, see Option in the CFX-Solver Modeling Guide.
Specify the Density and Molar Mass. An expression can be used for Density that depends on temperature and/or pressure. In this case, the CFX-Solver may build property tables in order to calculate enthalpy and entropy. If you use this option, check the table generation settings.
Additional information on Material Properties is available in:
If you set the specific heat capacity using a CEL expression, the solver will build tables for enthalpy and entropy. If you use this option, check the table generation settings.
For an ideal gas, specify the Molar Mass. For details, see Molar Mass in the CFX-Solver Modeling Guide.
Additional information on ideal gas is available in:
The Real Gas option can be specified to
model non-ideal gases and some liquid phase properties. Set Model to one of the following:
Aungier Redlich Kwong (the default model)
Peng Robinson
Soave Redlich Kwong
Standard Redlich Kwong.
To load the Real Gas materials into CFX-Pre:
On the Outline tab, right-click
Materialsand select Import Library Data.In the Select Library Data to Import dialog box, click Browse
and open the MATERIALS-redkw.ccl,MATERIALS-sredkw.ccl, orMATERIALS-pengrob.cclfile, which contain pre-defined real gas materials model.Select the group of materials to load and click .
Complete all of the data fields on the Materials Properties tab to use a Real Gas equation of state, then click .
Additional information on Real Gas models is available in:
Table uses a Real Gas Property (RGP) file to load real fluid property data (see Real Fluid Properties in the CFX-Solver Modeling Guide). You can load all of the RGP files that are supplied with CFX quickly by following the instructions given in Loading an .rgp file in the CFX-Solver Modeling Guide. When defining materials that use data in tables not supplied with CFX, the definition is carried out separately by specifying the filename and component name for each material in turn. When Table is selected, the following form appears:
RGP file Table Format is the only type supported for CFX.
Click Browse
beside Table Name to browse
to the file containing the Real Gas Property Table data.Enter the Component Name (as an RGP file can contain many components).
The component name corresponds to the name of a component in an RGP file. You may need to open the RGP file in a text editor to discover the exact name of the component you want to select. For details, see Detailed .rgp File Format in the CFX-Solver Modeling Guide.
For some equation of state and specific heat capacity settings (such as Redlich Kwong, IAPWS, and general materials having variable density and specific heat set with CEL expressions), the CFX-Solver builds internal property tables for efficient property evaluation. The most commonly required table is enthalpy as a function of temperature and possibly pressure. This table is built if the specific heat capacity is a function of temperature, and, possibly pressure. Entropy tables are also used to convert static and total pressure (or vice versa). For example, at a boundary condition you may specify the total pressure and the flow solver will use entropy tables to calculate the static pressure. When using CEL expressions for density and specific heat capacity the solver uses an adaptive algorithm to control the generation of the tables.
In some cases, it may be necessary to alter some table generation details, as described in the following sections:
The independent variable values of the table, represented by the row and column values, are established in accordance with the selected Table Generation > Option:
Uniform SpacingFor each of the two independent variables, points are distributed evenly across their respective range.
Adaptive SpacingFor each of the two independent variables, points are distributed unevenly across their respective range, with greater concentration where needed to resolve nonlinear variations in the dependent values.
Adaption of the table points occurs before starting a set of coefficient loops.
Adaptive Spacing and RangeThe table points are distributed using adaption, as for the
Adaptive Spacingoption. In addition, the range for each of the two independent variables is managed by the software in an attempt to provide adequate, but not excessive, coverage for the case being solved.
If Table Generation > Option
is set to Uniform Spacing or Adaptive Spacing,
the Min. Temperature and Max. Temperature
settings specify the lower and upper temperature bounds of
the table. The bounds should form a range somewhat wider than the expected temperature
range. To prevent having an overly large table, the specified range should not be wider
than the expected range by a factor much greater than 2.
If Table Generation > Option
is set to Adaptive Spacing and Range,
the Min. Temperature and Max. Temperature
settings are managed automatically, but can each be initialized by
selecting Initial Minimum Temperature/Initial Maximum Temperature
and entering a value.
These settings are analogous to the temperature settings described in Minimum and Maximum Temperature. As with the temperature bounds, any manually specified absolute pressure range should be somewhat wider than the expected range, but not by too much.
This setting specifies the maximum number of rows or columns. The default value of 100 is usually adequate.
Note: If the error tolerance cannot be met with the specified maximum number of points, the CFX-Solver may revert to a uniform table with a resolution set to the maximum number of points.
Table row and column values are established, in accordance with the chosen Table Generation > Option and subject to the specified value of Maximum Points, with the aim of limiting table cell interpolation error for dependent values to within the established tolerance.
The error tolerance, expressed as an amount of interpolation error normalized by the value that would be directly computed, is by default 0.01 for enthalpy and 0.03 for entropy.
If Table Generation > Option
is set to Uniform Spacing, the default tolerance applies.
If Table Generation > Option
is set to Adaptive Spacing or Adaptive Spacing and Range, you
can select Error Tolerance to specify a different tolerance value.
This controls the solver behavior when evaluating properties at temperatures or pressures beyond the table range. If extrapolation is activated, the property will be extrapolated based on its slope at the table boundary; otherwise, the value at the table boundary will be used. In either case, a message is written to the CFX-Solver Output file that an out-of-bounds has occurred. If this happens, you should consider increasing the table range accordingly.