In the Wet Steam model, the values of the total pressure and total temperature are computed using the isenthalpic and isentropic relations:

(14–566)

where the static values of the enthalpy and entropy are computed from the static pressure and temperature . If these static values of and are known from the solution, then the goal is to find such total values of and that and satisfy the equations in Equation 14–566.

This is done by solving the following system of equations obtained from the fundamental thermodynamic property relations:

(14–567)

The system is solved using Newton iterations until and become close to zero. The resulting and are assumed to be stagnation condition values.

The same procedure is used when, on the contrary, static values of and have to be evaluated from and , for example at a pressure inlet. In this case, the specified and are assumed to be stagnation condition values and the corresponding values of total enthalpy and entropy can be determined explicitly as and . The isenthalpic and isentropic relations is then read as:

(14–568)

and the system Equation 14–567 is solved until and become close to zero. The resulting and are assumed to be static values.

Ansys Fluent offers two options for the treatment of enthalpy and entropy when computing stagnation conditions values. One option is to compute and for the mixture of vapor and liquid droplets, the other is to use the vapor (gas) phase only. The latter is assumed in Ansys CFX and is referred to as the frozen assumption for dispersed phases. In Fluent, selection of either will give different total values in the regions with non-zero wetness, as well as different static values at pressure inlets unless zero wetness is specified there.