Equilibrium cavitation model (for pre-defined water only)

The homogeneous equilibrium approach is employed. It is applicable for a variety of important industrial processes.

The fluid is assumed to be a homogeneous gas-liquid mixture with the gaseous phase consisting of the vapor and non-condensable (dissolved) gas. The vapor mass fraction is defined at the local equilibrium thermodynamic conditions. The dissolved gas mass fraction is a constant, which can be modified by user.

The velocities and temperatures of the gaseous (including vapor and non-condensable gas) and liquid phases are assumed to be the same.

The following assumptions and limitations are made in the cavitation models:

In the Equilibrium Cavitation Model, cavitation is currently available only for the pre-defined water (when defining the project fluids you should select Water from the list of Pre-Defined liquids).
Cavitation process is assumed to be equilibrium.
The mixture is assumed to be a homogeneous two-phase fluid., the velocities and temperatures of the gaseous (including vapor and non-condensable gas) and liquid phases are assumed to be the same.
The model does not describe the detailed structure of the cavitation area, i.e. parameters of individual vapor bubbles and migration of bubbles.
The temperature and pressure in the phase transition area should be within the following ranges: 280.15 K < T < 583.15 K, 103 Pa < P < 107 Pa.
The volume fraction of vapor is limited by 0.95. The parameters of the flow at the initial and boundary conditions must satisfy this requirement.
The Cavitation option is not applicable if you calculate a fluid flow in the model without flow openings (inlet and outlet).
The fluid region where cavitation occurs should be well resolved by the computational mesh.
If the calculation has finished or has been stopped and the Cavitation option has been enabled or disabled, the calculation cannot be resumed or continued and must be restarted from the beginning.

The density of the gas-liquid mixture is calculated as:

	(1)

where v is the specific volume of the gas-liquid mixture, vl is the specific volume of liquid, zv(T,P) is the vapor compressibility ratio, Runiv is the universal gas constant, P is the local static pressure, T is the local temperature, yv is the mass fraction of vapor, μv is the molar mass of vapor, yg is the mass fraction of the non-condensable gas; μg is the molar mass of the non-condensable gas.

The properties of the dissolved non-condensable gas are set to be equal to those of air. By default, the mass fraction of non-condensable gas is set to 10-4. This is a typical model value appropriated in most cases but it can be modified by the user in the range of 10-3…10-5.

The mass fraction of vapor yv is computed numerically from the following non-linear equation for the full enthalpy gas-liquid mixture:

	(2)

where temperature of the mixture T is a function of pressure P and yv. Here hg, hl, hv are the enthalpies of non-condensable gas, liquid and vapor, respectively, k is the turbulent energy, Ic is the squared impulse defined as:

	(3)