Multiphase flow refers to the situation where more than one fluid is present. Each fluid may possess its own flow field, or all fluids may share a common flow field. Unlike multicomponent flow, the fluids are not mixed on a microscopic scale in multiphase flow. Rather, they are mixed on a macroscopic scale, with a discernible interface between the fluids. ANSYS CFX includes a variety of multiphase models to enable the simulation of multiple fluid streams, bubbles, droplets, solid particles, and free surface flows.

Two distinct multiphase flow models are available in ANSYS CFX,
an `Eulerian-Eulerian`

multiphase model and a `Lagrangian Particle Tracking`

multiphase model. Information
on the use of the `Lagrangian Particle Tracking`

model is available in *Particle Transport Modeling*.

This chapter describes how `Eulerian-Eulerian`

multiphase flow is modeled and also includes modeling advice. The
theory of multiphase flow is available; see Multiphase Flow Theory in the CFX-Solver Theory Guide.

The corresponding information for single-phase, single-component flow is available:

For information on the models used for single-phase flow, see

*Basic Capabilities Modeling*.For the mathematical implementation of the single-phase flow, see Basic Solver Capability Theory in the CFX-Solver Theory Guide.

For advice on modeling, see

*Advice on Flow Modeling*.

**Important:** Because this chapter extends the information given in the single-phase
documentation, you are advised to read the relevant sections in the
single-phase documentation before reading this chapter.

This chapter describes:

*Multiphase Terminology**Multiphase Examples**Eulerian-Eulerian Multiphase Versus Particle Transport**Specifying Fluids for Multiphase Flow**The Homogeneous and Inhomogeneous Models**Buoyancy in Multiphase Flow**Multicomponent Multiphase Flow**Interphase Momentum Transfer Models**Solid Particle Collision Models**Interphase Heat Transfer**Polydispersed, Multiple Size Group (MUSIG) Model**Turbulence Modeling in Multiphase Flow**Additional Variables in Multiphase Flow**Sources in Multiphase Flow**Interphase Mass Transfer**Boundary Conditions in Multiphase Flow**Modeling Advice for Multiphase Flow**Free Surface Flow**Algebraic Slip Model (ASM)**Multiphase Flow Restrictions*