Boiling and Condensation Model Reference


Theory	See Bulk Boiling.
Provided By	[phase interaction] > Models
Example Node Path	[phase interaction] > Models > Boiling/Condensation
Requires	Physics continuum selections: Material: Multiphase Multiphase Model: Mixture Multiphase (MMP) (Automatically activates: Multiphase Interaction, Gradients) Optional Models: Segregated Multiphase Temperature A liquid primary phase and a gas secondary phase that is the vapor of the liquid. For each phase: Material: Gas, Liquid A Phase Interaction model is required.
Properties	Key property: Relaxation Factor See Boiling/Condensation Properties.
Activates	Model Controls	First Dispersed Regime Nusselt Number See First Dispersed Regime Nusselt Number Properties. Second Dispersed Regime Nusselt Number See Second Dispersed Regime Nusselt Number Properties. Intermediate Regime Nusselt Number See Intermediate Regime Nusselt Number Properties .
	Field Functions	See Boiling/Condensation Field Functions.

Boiling/Condensation Properties

Relaxation Factor: Adjusts the model sensitivity. Reduce it to improve convergence.

First Dispersed Regime Nusselt Number Properties

The Nusselt number (

N u

) is the ratio of convective to conductive heat transfer across the boundary between two fluid phases (or a solid and a fluid phase). In laminar flow, the heat transfer from convection and conduction are of similar magnitude, so the Nusselt number is close to unity. The Nusselt number increases with more active convection. Typical values in turbulent flow are 100–1000, depending on the Reynolds number and other properties, such as the Prandtl number,

P r

.

A total of six Nusselt number ( $N u$ ) are specified. The First Dispersed Regime Nusselt Number, the Second Dispersed Regime Nusselt Number, and the Intermediate Regime Nusselt Number are specified for both the liquid side and the vapor side.

Controls the heat transfer rate to the boiling interface from the liquid side and the vapor side in the first dispersed regime (see Eqn. (2909)).

The Liquid and Vapor nodes have the following properties:

Method

Constant
Field Function
Field Function (Heat Transfer Coefficient)
Specifies the interphase heat transfer coefficient between liquid and vapor (W/m²-K).
Ranz Marshall
Available only for external heat transfer, that is, for the liquid side in the primary regime Eqn. (2043).

Second Dispersed Regime Nusselt Number Properties

Controls the heat transfer rate to the boiling interface from the liquid side and the vapor side in the second dispersed regime (see Eqn. (2909)).

The Liquid and Vapor nodes have the following properties:

Method

Constant
Field Function
Field Function (Heat Transfer Coefficient)
Specifies the interphase heat transfer coefficient between liquid and vapor (W/m²-K).
Ranz Marshall
Available only for external heat transfer, that is, the vapor side in the secondary regime Eqn. (2043).

Intermediate Regime Nusselt Number Properties

Controls the heat transfer rate to the boiling interface from the liquid side and the vapor side in the intermediate regime (see Eqn. (2909)).

Method

Constant
Field Function
Field Function (Heat Transfer Coefficient)
Specifies the interphase heat transfer coefficient between liquid and vapor (W/m²-K).
Hughes-Duffey
The liquid side heat transfer coefficient in the intermediate regime is calculated using the surface renewal theory introduced by Hughes and Duffey, see Eqn. (2070).
This method is available only when the primary phase has a turbulence model activated.

Calibration Factor

A calibration factor to adjust the Hughes-Duffey heat transfer coefficient. Increase this factor to increase the heat transfer coefficient value.

Boiling/Condensation Field Functions

MMP Boiling Mass Transfer Rate of [phase interaction]: The total mass transfer rate of both bulk and wall boiling. The mass transfer rate is positive if the mass transfer is from liquid to vapor ( $m^{(i j)}$ ) in Eqn. (2915).