You may also combine two materials together to create your own homogeneous binary mixture. To do this, first set up the two materials representing the two thermodynamic states.
It is very important that the two material definitions use consistent reference states for the enthalpy and entropy. The difference between the two material enthalpies must equal the latent heat at the selected reference temperature and pressure. To make this easier, CFX-Pre allows homogeneous binary mixtures to be created only from materials within the same material group.
When creating the homogeneous binary mixture, select the two materials that make up the mixture in the Material1 and Material2 fields. The thermodynamic state of one fluid should be liquid and the thermodynamic state of the other should be gas.
Under Saturation Properties, set the
Option to General. You must then set
the saturation properties (vapor pressure as a function of temperature) for the
mixture. This may be done in one of two ways.
If you choose to use constant saturation conditions, then, because they are dependent, you should set values for saturation pressure and temperature that are consistent. For example, for a mixture of saturated liquid and water vapor at 1 atm, the saturation temperature is 100 °C; for a mixture of saturated liquid and water vapor at 100 °C, the saturation pressure is 1 atm.
If you use CEL expressions or User Fortran for both pressure and temperature,
you should ensure that your function or expression guarantees that
for all 
on the
saturation curve.
You can choose to use this equation for the saturation pressure and supply the flow solver with the necessary model constants. These are tabulated in several thermodynamics texts, see, for example, [84]. Automatic is the only option allowed for temperature in this case because the flow solver calculates saturation temperature from the Antoine equation.
The Antoine Equation correlates vapor pressure as a function of temperature using three coefficients as follows:
 | (12–8) |
where 
is the Pressure Scale used to scale the units for the vapor
pressure, 
is the Antoine Reference State
Constant, 
is the Antoine Enthalpic Coefficient
and 
is the Antoine Temperature
Coefficient. Depending on the reference you use to obtain the constants, Equation 12–8 can also be written in different
forms, so some care should be taken when entering coefficients from the
literature. For example, the tables in [84] assume that the Antoine equation is written as
follows:
 | (12–9) |
where 
is in bars and
is 1.0 bar. So, if you are running the flow solver in the SI
unit system, this requires that you add 5.0 to 
and multiply
that result by the natural logarithm of 10.0, multiply 
by the natural
logarithm of 10 and subtract 273.15 K from the tabulated values of 
. If you are
running in a non-SI unit system this would require that you also convert the
constants to return the right units of pressure.