Case 2: PLvap < P < PHvap (liquid + vapor, cavitation)

We assume a volume fraction of vapor θ = θ(P). For one unit volume of fluid there is θ volume of vapor and of (1 -θ) volume of liquid:

We assume that between the two vapor pressures and , the volume fraction of vapor varies linearly in function of pressure:

Equation 13: Volume fraction of vapor

In order to have a higher degree of continuity at the boundary conditions θ=0 at and θ=1 a t, we use in fact a polynomial interpolation between the two extreme pressures:

with

Equation 14: Simcenter Amesim law with higher degree of continuity

Figure 21: Volume fraction of vapor (cavitation)

The curve used is sufficiently smooth at and not to require discontinuity handling.

The mass of {liquid+vapor} is:

The volumetric fraction θ gives the density of {liquid+vapor}:

Equation 15: Density of mixture {liquid + vapor} at P and T

Where the density of vapor is

The volume of liquid part is:

From this, we can compute the volumetric air fraction Φ:

Where:

And the fluid density will be: