Two-Phase Thermodynamic Equilibrium (TPTE) Model Reference

In this model, the computational effort is reduced by assuming the suspension to be a homogeneous single-phase system. The distribution of static enthalpy, and the assumption of thermodynamic equilibrium, are used to calculate the distribution of phases.

Table 1. Two-Phase Thermodynamic Equilibrium Model Reference
Theory	See Two-Phase Thermodynamic Equilibrium.
Provided By	[physics continuum] > Models > Multiphase Model
Example Node Path	Continua > Physics 1 > Models > Two-Phase Thermodynamic Equilibrium
Requires	Pre-requisite selections: Material: Multiphase Multiphase Model: Two-Phase Thermodynamic Equilibrium This model is compatible only with single-component phases.
Activates	Physics Models	Automatically selected models: Multiphase Interaction Phase interaction models: Two-Phase Equilibrium Interaction (activated automatically in a phase interaction) Algebraic Slip (available for segregated flow only) See Algebraic Slip Model Properties. Drift Flux (available for both coupled flow and segregated flow) See Drift Flux Model Wall Boiling (the Gravity model must be activated in the physics continuum) See Wall Boiling Models.
	Materials	Dynamic Viscosity Specific Heat Thermal Conductivity Turbulent Prandtl Number See Materials and Methods.
	Boundary Inputs	See Boundary Settings.
	Region Settings	Physics Conditions: Energy Source Option Initial Condition Option Momentum Source Option Turbulence Source Option (for Turbulent viscous regimes) See Region Settings.
	Solvers	Segregated Flow Segregated Energy Coupled Implicit
	Field Functions	Mass Fraction of [phase] Specific Heat of [phase] Thermal Conductivity of [phase] Static Enthalpy at Saturation Temperature of [phase] See Field Functions.

Algebraic Slip Model Properties

Velocity Ratio: Specifies the slip velocity ratio. This value is $S$ in Eqn. (2954).
This value can be defined as a constant or as a field function (typically user-defined).

Drift Flux Model

The drift ﬂux model takes into account the relative motion between phases by a constitutive relation. The energy contributions are limited to avoid sub-cooled water or superheated steam.

Under-Relaxation Factor: Under-relaxes both momentum and energy sources calculated by the drift flux model in Eqn. (2938) and Eqn. (2939). If the drift flux model is the suspected cause of numerical oscillations in the simulation, reduce this factor to aid stability. The default value is 1.0.

Max Acceleration Change: Limits the drift flux contribution to the momentum equations in Eqn. (2938). This expert property is expressed in terms of maximum acceleration threshold. This threshold represents the upper limit of the drift flux momentum source compared to a gravitational force. The default value is 10.0, which is considered to be a reasonable value for most cases.

The correlation in drift ﬂux model is done by specifying the two parameters that define the drag force acting on the gas phase. These two parameters are:

Distribution Parameter

Specifies the distribution factor that reflects non-uniformity in the void fraction and velocity distribution. This value is $C_{0}$ in Eqn. (2944).

This value can be defined as a constant – a single three-part (or two-part for two-dimensional), comma-separated, number – or as a field function (typically user-defined).

Drift Velocity

Specifies the volume-weighted mean drift velocity. This value is $v_{d r}$ in Eqn. (2944).

This value can be defined as a constant, a field function (typically user-defined), or as a composite. A composite value has three components (for example, X, Y, Z) for three-dimensional problems, or two components (for example, X, Y) for two-dimensional problems.

Wall Boiling Models

The following wall boiling models are available:

Rohsenow Boiling: See Rohsenow Boiling Model Properties.
Transition Boiling: See Transition Boiling Model Properties.

Materials and Methods

Dynamic Viscosity: The dynamic (shear) viscosity of the fluid mixture is a measure of its resistance to shearing flows. This value is $μ_{m}$ in the formulation. Computed using the Volume-Weighted Mixture method.

Specific Heat

The specific heat of the fluid mixture is the ratio of the heat added to the mixture and the resulting temperature change. This value is $C_{p}$ in the formulation. Computed using the Mass-Weighted Mixture method.

See Phase Coupled Fluid Energy Model Reference.

Thermal Conductivity: The thermal conductivity of the fluid mixture is a measure of the ability of the mixture to conduct heat. This value is $λ$ in the formulation. Computed using the Volume-Weighted Mixture method.

Turbulent Prandtl Number: The Turbulent Prandtl Number is the ratio of the momentum eddy diffusivity and the heat transfer eddy diffusivity in the fluid mixture. It is used in modeling heat transfer in turbulent boundary layer flows.
Activated when the Turbulent model is selected in the Viscous Regime.

Boundary Settings

No drift flux contributions are accounted for at inflow boundaries. An inflow boundary condition that includes a drift flux would imply that phase transfer (such as boiling or condensation) is taking place at the boundary. When using the Two-Phase Thermodynamic Equilibrium model, set the inflow boundary in a location where a homogeneous phase mixture enters the domain—not in a location where phase transfer occurs.

Inflow Boundaries

Volume Fraction: The ratio of the volume that each phase occupies to the computational cell volume.; When you specify boundary values, there is no restriction on the values that you can set for the volume fractions of the phases. However, Simcenter STAR-CCM+ uses normalized values for each phase volume fraction to ensure that the total volume fraction is 1.0.

Pressure Outlet

Volume Fraction

The ratio of the volume that each phase occupies to the computational cell volume.

This setting is relevant only when you have backflow. If you do not have backflow, ignore this setting.
If you have backflow, and only one phase is present at the pressure outlet, set the volume fraction of that phase to 1.
If you have backflow and a mixture of phases is present at the outlet, it is unlikely that the pressure outlet correctly captures your physics. (A pressure outlet assumes a constant pressure across the outflow interface.) You are advised to make your domain larger so that backflow no longer occurs.

Region Settings

Energy Source Option

Lets you specify energy source options for an individual region.

See Energy Source Option.

Initial Condition Option

Lets you customize initial conditions for an individual region.

See Setting Initial Conditions for a Particular Region.

Momentum Source Option

Method	Corresponding Physics Value Nodes
Momentum Source Option None Specified Adds a specified momentum source to the momentum equation.	When the Specified method is selected: Momentum Source Momentum Source Velocity Derivative See Momentum Source Option.

Method

Corresponding Physics Value Nodes

Momentum Source Option

None
Specified

Adds a specified momentum source to the momentum equation.

When the Specified method is selected:

Momentum Source
Momentum Source Velocity Derivative

See Momentum Source Option.

Turbulence Source Option

Available when a turbulence model is activated in the physics continuum.

Method	Corresponding Physics Value Nodes
Turbulence Source Option None Specified Ambient	When the Specified method is selected: Specific Dissipation Rate Source Available for the K-Omega turbulence model. See K-Omega Regions Reference. Turbulent Kinetic Energy Source Available for both the K-Omega and K-Epsilon turbulence models. Turbulent Dissipation Rate Source Available for the K-Epsilon turbulence model. Turbulent Dissipation Rate Source Derivative Available for the K-Epsilon turbulence model. Turbulent Kinetic Energy Source Derivative Available for the K-Epsilon turbulence model. See K-Epsilon Regions Reference. When the Ambient method is selected: Ambient Turbulence Specification

Method

Corresponding Physics Value Nodes

Turbulence Source Option

None
Specified
Ambient

When the Specified method is selected:

Specific Dissipation Rate Source

Available for the K-Omega turbulence model.

See K-Omega Regions Reference.

Turbulent Kinetic Energy Source

Available for both the K-Omega and K-Epsilon turbulence models.

Turbulent Dissipation Rate Source

Available for the K-Epsilon turbulence model.

Turbulent Dissipation Rate Source Derivative

Available for the K-Epsilon turbulence model.

Turbulent Kinetic Energy Source Derivative

Available for the K-Epsilon turbulence model.

See K-Epsilon Regions Reference.

When the Ambient method is selected:

Ambient Turbulence Specification

Field Functions

Mass Fraction of [phase]: The ratio of the mass of the particular phase to the total mass in the cell.
Specific Heat of [phase]
Thermal Conductivity of [phase]
Static Enthalpy at Saturation Temperature of [phase]