Evaporation/Condensation Model Reference

This model is available in a Film-VOF Phase Interaction (for a hybrid Film-VOF simulation) and in a Film-Physics Continuum Interaction (for all other simulation types).

The Fluid Film Evaporation and Condensation model is implemented as a diffusion limited model. For that reason, it is not directly applicable to regimes where energy transport dominates the phase exchange. For example, during condensation of pure vapor or when evaporation takes place close to boiling point. In such saturated regimes, you can switch to using the thermally limited evaporation and condensation model.

Evaporation/Condensation Model Properties

Thermal Limitation

Thermal limitation prevents infinite evaporation rates even for temperatures equal to the saturation temperature. This model limits the amount of heat that can be transported away from or towards the interface to compensate for the change in latent heat due to the phase change.

• Activated: The solver uses the thermally limited implementation of the evaporation and condensation model. This model is used for saturated regimes, for example, during condensation of pure vapor or when evaporation takes place close to the boiling point. This option is the default.
• Deactivated: The solver uses the hydrodynamically limited evaporation and condensation model. This model is used for non-saturated regimes.

For more information, see Evaporation and Condensation Solution Procedure.

Under-Relaxation Factor

At each iteration, this property governs the extent to which the newly computed solution supplants the old solution. If the evaporation process is very intensive, convergence or stability issues can arise. If necessary, reduce this value to enhance convergence and to stabilize the simulation.

Saturation Threshold

The saturation ratio that is used in Eqn. (2799) to determine whether saturation occurs. This setting lets you adjust when the fluid film evaporation and condensation model switches into saturation mode.

Nucleation Density

The nucleation density for evaporation and condensation droplets. This value is $N$ in Eqn. (2801).

For more information, see Steam Condensation at a Dry Wall.

Minimum Nuclei Radius

The minimum radius of evaporation and condensation droplets. This value is $R_{\min }$ in Eqn. (2801).

The nucleation density and the minimum radius of evaporation and condensation droplets that you specify define a limiting film thickness. Below this limit, the film is assumed to be a drop-wise distribution of liquid, rather than a flat distribution of liquid along the whole shell area. The number of droplets is calculated from the nucleation density, and the droplet radius is obtained from the film thickness. If the calculated droplet radius is smaller than the specified minimum nuclei radius, the minimum nuclei radius is used.

When the interface area that is calculated based on a drop-wise distribution of liquid is smaller than the shell area, the smaller area is used for calculating the mass and energy sources due to evaporation and condensation. This reduction in the interface area can slow down the phase exchange. However, if the interface area of the drop-wise distribution of liquid is larger than the shell area, the phase exchange is not improved. The shell area is used for all calculations.

For more information, see Steam Condensation at a Dry Wall.

Linearize Film Energy Source

When activated, the effect of phase exchange is linearized in the film energy equation.

Linearize Gas Energy Source

When activated, the effect of phase exchange is linearized in the gas energy equation.

Condensation

When activated, condensation is included in the phase interaction.

Evaporation

When activated, evaporation is included in the phase interaction.

Material Properties

Available when any energy model is included with Fluid Film simulations. These material properties can be set for each for each component of film multi-component phases:

Heat of Formation

The heat that is evolved when 1 kilogram of the material is formed from its elements in their respective standard states [J/kg]. See Using the Heat of Formation.

Latent Heat of Vaporization

Available at the component level for multi-component phases.

Method	Corresponding Method Node
Enthalpy Difference	Enthalpy Difference This node provides no properties. See Using the Enthalpy Difference Method for Latent Heat of Vaporization.

For Simcenter STAR-CCM+ In-cylinder with Fluid Film simulations this property can be specified using a constant scalar profile, field function, Polynomial in T, or Table(T) method.

Saturation Pressure

The saturation pressure $p_{sat}$ is the pressure of each vapor component when in equilibrium with the corresponding liquid component. This value is required for each liquid component, it can be specified as a Field Function, Polynomial in T, Table (T) or one of the following:

Method	Corresponding Method Node
Antoine Equation	Antoine Equation Defines the saturation pressure using the Antoine equation. See Using the Antoine Equation.
Wagner Equation	Wagner Equation Defines the saturation pressure using the Wagner equation. See Using the Wagner Equation.

Standard State Temperature

The temperature at which the standard state of the material is defined. See Using the Standard State Temperature.

Critical Temperature

The temperature above which the material cannot be liquefied, regardless of the pressure that is applied. This value is required for each liquid component.

Evaporation/Condensation Model Field Functions

The following primitive field functions are made available when the Fluid Film Evaporation and Condensation model is activated. They allow you to monitor how fast evaporation or condensation occurs.

Film Evaporation Latent Heat Flux	The latent heat due to evaporation (W/m2) that is injected at the interface.
Film Evaporation Rate	The rate of evaporation in kg/m2-s for every species.
Film Evaporation Mass Fraction	The saturated vapor mass fraction on the gas side of the interface, for every interacting component.