Setting Up Fluid Film Evaporation and Condensation

To model fluid film evaporation and condensation, you set up the appropriate phase interaction model, activate the fluid film Evaporation-Condensation model, and set the property values according to your simulation.

Before you begin, you need the following:
  • A simulation with the Fluid Film model activated.
  • The fluid film phase defined as a multi-component liquid.
  • The corresponding Eulerian phase (for the VOF Multiphase model) or the physics continuum defined as a multi-component gas.
To model fluid film evaporation and condensation:
  1. Select the physics models that are required for a fluid film simulation. Include the following models:

    • Multi-Component Gas material model in the physics continuum.

    • Multiphase Interaction model in the physics continuum.

    • If you want to model the effect of evaporation and condensation on the heat balance, select either Coupled Energy or one of the Segregated Fluid Energy models.

  2. Create a multiphase interaction and select the fluid film phase and the corresponding vapor phase.

    The phase interaction type is determined automatically:

  3. Set up the phase interaction:
    • Activate the Component Mapping model.
    • Activate the Evaporation-Condensation model.
    • If you are modeling a Film-Physics Continuum interaction simulation, to evaluate the vapor pressure in the multi-component liquid, select one of the following methods for calculating the activity coefficient:
    • Raoult's Law—use this option if the components in a multi-component liquid are chemically identical. This method is selected automatically when selecting the Evaporation-Condensation model. To choose another method to calculate activity coefficient, you need to unselect this option first.
    • Modified UNIFAC—use this option if the components in a multi-component liquid are significantly dissimilar in terms of molecular structure. See Evaporation-Condensation.
  4. In the Component Mapping node, map the components of the two phases.
  5. Select the Evaporation-Condensation node and set the property values according to your simulation.

    If the evaporation process is very intensive, convergence or stability issues can arise. To resolve these issues and to stabilize the simulation, you are advised to under-relax the change of the evaporation rate by reducing the Under-Relaxation Factor.