Modeling Particulate Flows

Particulate flows describe multiphase flow regimes that deal with gas-solid or liquid-solid flows. Examples of these flows are fluidized beds, pneumatic conveyors, and cement.

The steps in this procedure are intended to follow on from Step 5 in Modeling Eulerian Multiphase Flow.

A particulate flow simulation requires a minimum of two Eulerian phases: a fluid phase and a solid particle phase. Each particle phase consists of particles of the same material. To model particles of different materials, you create additional particle phases and specify the appropriate particle material for each phase. By default, all of the particles in a particle phase are the same size. If you want to specify a range of particle sizes, select the appropriate particle size distribution model.

To model particle-phase flows:

For the [physics continuum] in which you are modeling particulate flows, select the following models in addition to the models that you previously selected:


Group Box	Model
Optional Models	To consider particle-particle interactions, select one of the following models: Granular Pressure Use this model if the particles are loosely packed, such as fluidized beds. This model introduces the concept of the “packing limit”. Below this limit, particles are loosely packed and inter-particle collisions determine their motion. Above the packing limit, friction between particles dominates their motion. It is possible to work with multiple particle phases (that is, particles of different sizes) with this model. The Granular Temperature and the Granular Temperature Transport models are selected automatically. See Granular Pressure Model Reference. Solid Pressure Use this model if the particles are packed closely together. This model is provided for dispersed particle phases to account for the forces that arise during particle-particle interaction. It is a way of limiting the maximum particle volume fractions. See Solid Pressure Model Reference. If the fluid consists of solid particles suspended in a liquid, select Suspension Rheology. The Laminar viscous regime must be selected in the physics continuum. See Modeling Suspensions.

Create two Eulerian phases, typically one fluid phase and one particle phase.

For each phase, right-click the Multiphase > Eulerian Phases node and select New.

For the fluid phase (gas or liquid), right-click the [fluid phase] > Models node and, 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
Reaction Regime	(For multi-component phases only) Select one of the following: Non-reacting Reacting
Equation of State	Any See General Equation of State Models.
Reynolds Averaged Turbulence	For a Turbulent viscous regime, select one of the following: K-Epsilon K-Omega Reynolds Stress Turbulence Response See Modeling Turbulence.
Energy	Select one of the following: Segregated Fluid Enthalpy Segregated Fluid Temperature
Optional Models	If you want to track the phase material within the simulation, select Passive Scalar. See Modeling Passive Scalars.

For the particle phase, in the Phase Model Selection dialog, select the following models:


Group Box	Model
Material	Select one of the following: Particle Multi-Component Particle
Reaction Regime	(For multi-component particles only) Select one of the following: Non-reacting Reacting
Reynolds-Averaged Turbulence	Select one of the following: K-Epsilon Turbulence K-Omega Turbulence Reynolds Stress Turbulence Turbulence Response If you selected the Granular Pressure model, the following models are selected automatically: Reynolds Averaged Navier-Stokes K-Epsilon Turbulence Standard K-Epsilon Wall Distance Granular Wall Treatment See Modeling Turbulence.
Energy	Select one of the following: Segregated Fluid Enthalpy Segregated Fluid Temperature
Optional Models	Erosion (available only when the Granular Pressure model is selected) Models the effects of erosion, such as impact erosion or abrasive wear on a wall, by the particles. See Erosion Model Reference.

If you want to model the non-Newtonian behavior of solid particles suspended in a liquid, reopen the Physics Model Selection dialog for the physics continuum and select the Suspension Rheology model from the Optional Models group box.

The Laminar viscous regime must be selected in the physics continuum.

See Modeling Suspensions.
If you want to predict the size distribution of the solid particles, follow the steps in one of the additional workflows. Otherwise, the particle size is constant for each particle phase that you define.

See Modeling Adaptive Multiple Size-Group Particle Size Distribution.

See Modeling S-Gamma Particle Size Distribution.

Specify the density and diameter of the particles in the particle phase.

Select the [particle phase] > Models > Particle > [particle material] > Material Properties node and set the Density and Particle Diameter values.

Set the maximum solid fraction of the particle phase.

Select the [particle phase] > Models > Granular Pressure node and, in the Properties window, set the Maximum Solid Fraction.

Specify the particle coefficient of restitution.

Select the [particle phase] > Reference Values > Coefficient of restitution node and, in the Properties window, set the Value.
See Reference Values.

For each phase, set the initial volume fraction and the initial velocity. For the particle phases, you also set the initial granular temperature profile.

Select the [phase] > Initial Conditions node and set the Velocity, Volume Fraction, and (for particle phases) Granular Temperature values.
See Initial Conditions.

Define the appropriate phase interactions.

Right-click the Models > Multiphase Interaction > Phase Interactions node and do one of the following:
- To model the interaction between the fluid phase and a particle phase, select New > [Fluid Phase] > [Particle Phase].
  
  See Continuous-Dispersed Topology.
- To model the interaction between two particle phases, select New > [Particle Phase 1] > [Particle Phase 2].
  
  See Granular Particle Pair Phase Interaction.
Right-click the [phase interaction] > Models node and click Select Models.

In the Phase Interaction Model Selection dialog, select additional phase interaction models.


Group Box	Models
Optional Models	Lift Force Models the effect of the lift force on the particle phase. See Lift Force Model Reference. Drag Force See Drag Force Model Reference. Interphase Energy Transfer Models energy transfer between the phases. See Interphase Energy Transfer Model Reference. Interphase Mass Transfer Models mass transfer between the phases, such as crystalization. See Interphase Mass Transfer Model Reference. Particle Induced Mixing or Particle Induced Turbulence Source These models account for the modification of turbulence due to the presence of the particle phase. 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 particle phase density is similar or smaller than the continuous phase density. See Virtual Mass Force Model Reference. Virtual Stress See Virtual Mass Stress Model Reference.

If you selected Interphase Mass Transfer, follow the steps in the additional workflows. The following mass transfer types are available:


Mass Transfer Type	Description
Crystalization	Crystalization of a single multi-component phase is modeled with the Single Component Crystal Growth models. See Modeling Crystallization.
User-Defined Interphase Mass Flux	This model 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.

Set the phase interaction model properties.

For a Continuous-Dispersed phase interaction, you specify the contribution to the granular energy transport that is due to the correlation between the velocity fluctuations of the gas and the particles.

Select the [phase interaction] > Models > Granular Energy Transfer node and, in the Properties window, specify the Cross-Correlation Term.
See Granular Energy Transfer Model Reference.

For a Granular Particle Pair Phase Interaction, you specify the coefficient of restitution for collisions between particles.

Select the [phase interaction] > Reference Values > Coefficient of restitution node and, in the Properties window, set the appropriate value.

See Granular Particle Pair Phase Interaction Reference Settings.

At each open boundary, set the volume fraction and velocity of each phase.

Select the [boundary] > Phase Conditions > [phase] > Physics Values node and set the Velocity and Volume Fraction values.

Set the granular temperature for each particle phase at each boundary. The granular temperature value that you specify is used to calculate the solid pressure at the boundaries, which has a significant influence on the simulation results.

At each wall boundary, specify the shear stress for each particle phase.

Select the [boundary] > Phase Conditions > [particle phase] > Physics Conditions node and set the Granular Temperature Specification and Shear Stress Specification.
See Boundary Settings.

If you are modeling the effects of erosion by the particles, specify the type of erosion to model at each wall boundary.

Select the [boundary] > Phase Conditions > [particle phase] > Physics Conditions > Erosion Specification node and select the appropriate method.

In the corresponding Physics Values node, set the appropriate property values.

See Erosion Model Reference.

Specify the appropriate solver settings.

Select the Solvers > Granular Temperature node and, in the Properties window, set the Under-Relaxation Factor to the appropriate value.
See Granular Temperature Solver.

Return to Modeling Eulerian Multiphase Flow and continue with Step 6.