Modeling Bubbly and Droplet Flows

Bubbly and droplet flows are where one liquid or gas phase is dispersed within another liquid or gas phase throughout the domain at all times.

The steps in this procedure are intended to follow on from Step 4 in Modeling Eulerian Multiphase Flow.

To model bubbly and droplet flow:

Create two Eulerian phases, typically one gas phase and one liquid phase. For each phase:

Right-click the Multiphase > Eulerian Phases node and select New.
Right-click [phase] > Models and click Select Models.

In the Phase Model Selection dialog, select the following models:


Group Box	Model
Material	Select one of the following: Gas Liquid Multi-Component Gas Multi-Component Liquid To model chemical reactions, select each phase to be multi-component. For information on working with single-component materials, see Managing single-component materials. For information on working with multi-component materials, see Managing multi-component materials. This latter section includes details on adding individual mixture components.
Reaction Regime	Select one of the following: If no reactions occur, select Non-reacting To model chemical reactions or combustion, select Reacting. Combustion in a multiphase flow has applications that include fluid catalytic cracking, fluidized beds, and riser flow. Select further models from the Reacting Species Models group. For more information, see Reacting Species Transport Workflow.
Equation of State	Any See General Equation of State Models.
Reynolds Averaged Turbulence	Select one of the following: K-Epsilon K-Omega Reynolds Stress Turbulence Response See Modeling Phasic Turbulence.
Energy	Select one of the following: If you want to model intraphase chemical reactions or combustion, select Segregated Fluid Enthalpy This model is required for each phase in which you want to use chemical reactions or combustion. Segregated Fluid Temperature
Optional Models	Select any number of the following: User Potential Force If you have a two-phase simulation with one gas phase and one liquid phase, you can model potential forces such as capillary pressure and osmotic pressure. See Modeling Potential Forces. Passive Scalar Used for tracking the phase material within the simulation. See Modeling Passive Scalars. Particle Size Distribution Use to predict the size distribution of droplets and bubbles due to breakup and coalescence. Select one of the following Particle Size Distribution models: Adaptive Multiple Size-Group See Modeling Adaptive Multiple Size-Group Particle Size Distribution. S-Gamma See Modeling S-Gamma Particle Size Distribution. Otherwise, the droplet or bubble size is constant for each dispersed phase that you define.

Define the phase interaction between the continuous and the dispersed phase. When you create a phase interaction, you select the continuous phase first, and then the dispersed phase. When you select the dispersed phase, you also choose the phase interaction type.

Right-click the Models > Multiphase Interaction > Phase Interactions node and select New > [Continuous Phase] > [Dispersed Phase] (Continuous-Dispersed).

Open the Phase Interaction Model Selection dialog and select additional phase interaction models.


Group Box	Model
Enabled Models	Drag Force (selected automatically) See Drag Force Model Reference. Interaction Length Scale (selected automatically) See Interaction Length Scale Model Reference. Interaction Area Density (selected automatically) See Interaction Area Density Model Reference. Multiphase Material (selected automatically)
Optional Models	Select any of the following: Lift Force Accounts for the lateral motion of bubbles due to velocity gradients in the continuous phase. See Lift Force Model Reference. Wall Lubrication Force Models the effect of walls on a bubbly flow. See Wall Lubrication Force Model Reference. Particle Induced Turbulence Source See Particle Induced Turbulence Source. Turbulent Dispersion Force Models the interaction between the dispersed phase and the surrounding turbulent eddies. See Turbulent Dispersion Force Model Reference. Virtual Mass Force Accounts for resistance effects when the dispersed phase density is similar or smaller than the continuous phase density. See Virtual Mass Force Model Reference. Interphase Energy Transfer Models energy transfer between the phases. See Interphase Energy Transfer Model Reference. Emulsion Rheology Models the phases as an emulsion. This option is available when both the continuous phase and the dispersed phase are liquid phases. See Emulsion Rheology Model Reference. See Modeling Emulsions.

If you want to set up heat and mass transfer, follow the steps in the additional workflows. The following mass transfer types are available:


Mass Transfer Type	Description
Boiling	Bulk boiling and condensation is modeled with the Boiling Mass Transfer Rate model. The boiling model is not suitable for describing boiling without bubbles (homogeneous nucleation), evaporation (concentration-driven multi-component mass transfer), nor cavitation (inertially-limited mass transfer). This model is also unsuitable when the resulting interphase mass transfer rate occurs on time scales that are much shorter than that of the flow. See Modeling Boiling.
Diffusion	The Dissolution Mass Transfer Rate model accounts for transfer between the components of each phase. This model handles the case where one phase is liquid and one phase is gaseous, and the case where both phases are liquid. Both of the phases must be multi-component. See Modeling Dissolution Mass Transfer.
Droplet Evaporation	Evaporation and condensation is modeled with the Droplet Evaporation Mass Transfer Rate model. Depending on whether the liquid droplet is single or multi-component, the Single Component Droplet Evaporation Mass Transfer Rate model or the Multicomponent Droplet Evaporation Mass Transfer Rate model is used. This model assumes that the liquid drops are internally homogeneous and that the liquid behaves like an ideal mixture. The presence of inert components is allowed in both the gas and the liquid. See Modeling Droplet Evaporation.
Interphase Reaction	Interphase reactions are modeled with the Interphase Reaction model. Both of the phases must be multi-component. See Modeling Interphase Reactions.
User-Defined Interphase Mass Flux	This model is available when the Interphase Mass Transfer model is selected. It assumes that the effect of interphase mass transfers on the phase temperatures is negligible. If the Phase Coupled Fluid Energy model is already activated, then select the Interphase Energy Transfer phase interaction model to make sure that the phase temperatures reach sensible values.

Return to Modeling Eulerian Multiphase Flow and continue with Step 5.