### 12.5.2. Inlet Boundary Conditions

If you are using the total pressure and total enthalpy boundary condition with the equilibrium phase change model then you do not have to set the equilibrium fraction, this is automatically derived for you by the flow solver. If the value is set, then the flow solver will ignore it.

Alternatively, if you are using the total pressure and total temperature boundary condition with the equilibrium phase change model, you have the option to enter the value of the equilibrium fraction.

The flow solver applies the specified value of equilibrium fraction as a “total” equilibrium fraction value. If the total conditions are dry vapor, this does not necessarily mean that the static conditions are also dry. For example, if the inlet equilibrium fraction is set to be all vapor (total quality is 1), then the flow solver uses the specified total temperature and pressure, as a starting point to determine the static conditions. If the total conditions were just above the saturation dome, then it is very likely that the final static condition is under the dome and the inlet condition will be a bit wet.

If you specify a value for quality between zero and unity then you are saying that the inlet total conditions are under the dome, and total temperature and pressure are no longer independent. In this case, to ensure consistency with the properties, the flow solver ignores the specified total temperature and evaluates total temperature from the vapor pressure curve instead, that is, .

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