Defining the Phase Interaction Properties

Define the interactions between the phases.

The main modeling choice that is made here is the use of the combination of Hibiki-Ishii Nucleation Site Number Density and Kocamustafaogullari Bubble Departure Diameter. This combination of models is applicable for water boiling under a wide range of pressures. The default models (Lemmert-Chawla and Tolubinsky) are much simpler, but can need testing and recalibration for use at different pressures.

As a wide range of volume fractions is expected, ensure that the Interaction Area Density model uses the Symmetric method.

To define the phase interaction properties:

  1. Edit the Liquid Vapor Interface > Models node and set the following properties:
    Node Property Setting
    Boiling Mass Transfer Rate > Continuous Phase Nusselt Number Method Ranz-Marshall
    Disperse Phase Nusselt Number Value 26.0
    Drag Force > Drag Coefficient Method Tomiyama
    Drag Correction Method Volume Fraction Exponent
    Volume Fraction Exponent (continuous) 0.0
    Interaction Area Density > Interaction Area Density Method Symmetric
    Interaction Length Scale > Interaction Length Scale Method Field Function
    Scalar Function ClippedSauterMeanDiameter
    Wall Bubble Nucleation > Nucleation Site Number Density Method Hibiki-Ishii
    Bubble Departure Diameter Method Kocamustafaogullari


    Selecting the Ranz-Marshall option makes Simcenter STAR-CCM+ calculate the Continuous Phase Nusselt Number using the Ranz-Marshall correlation. The Ranz-Marshall correlation, in turn, is used to calculate the heat transfer coefficient for the heat transfer from the bulk water to the bubble interface.

    The Disperse Phase Nusselt Number is used when calculating the heat transfer coefficient for the heat transfer from the bubble interface to the bulk steam. The exact value is not critical because the vapor is going to be at, or close to, saturation temperature. A value of 2 represents a slow response with little internal circulation. A higher value such as 26 can represent either a fast superficial response or the effect of internal mixing within the vapor.

    The Tomiyama model is used for modeling bubbly flows. Drag reduction is not expected for small spherical bubbles.

    The Turbulent Dispersion Force setting is important for wall boiling calculations in the presence of condensation because it treats the differencing of rapidly changing volume fraction gradients more accurately. Without this setting, the simulation can get unusual velocities at the edge of the spreading bubble cloud as well as unnecessary convergence difficulties.

    The Interaction Length Scale is based on the bubble size predicted by the S-Gamma model. The ClippedSauterMeanDiameter field function is one of the user-defined field functions that was created earlier. This setting allows the Sauter Mean Diameter that is predicted with the S-Gamma model to be used as the interaction length scale for drag and interface transfers. It also filters the calculations through a maximum and a minimum diameter so that early unconverged S-Gamma solutions do not upset convergence.

  2. Select the Physics 1 > Models > Multiphase > Phases > Vapor > Models > Issa Turbulence Response Model node and set the Phase Interaction to Liquid Vapor Interface.
  3. Save the simulation.