## Multiphase Flow Modeling : Part 2 - Terminologies

The terminologies used in the study of multiphase flows are as follows :

**Continuous phase or Primary phase : **This is basically the carrier fluid, that is present in bulk.

**Dispersed phase or Secondary phase**** : **This is the discrete phase which is usually in the form of particles, droplets, or bubbles.

The secondary phase may or may not have a distinct velocity field i.e. it will at some times follow the continuous phase or at times will have its own velocity field.

**Volume fraction :**

**It is defined as the ratio of volume of dispersed phase to the volume of the medium or the total volume. Mathematically represented by :**

*Volume fraction of a dispersed phase*:

**Similarly, defined as the ratio of volume of continuous phase to the volume of the medium or the total volume. Mathematically represented by**

*Volume fraction of a continuous phase*:where del Vc is the volume of the continuous phase in the volume. By definition the sum of the volume fraction must be unity i.e.

**Densities :**

**Velocities :**

There are generally two terms used to define velocities, the superficial velocity and the phase velocity.

* Superficial Velocities :* It is mostly associated with pipe flow and is the mass flow rate, of the respective phase divided by the pipe area A and material density. So in case of dispersed phase this superficial velocity is given by:

* Phase velocities : *The phase velocity Ud is the actual velocity of the phase. The volume fraction relates the phase velocity with the superficial velocity as follows :

**Mass concentration of dispersed phase :**

It is the ratio of the mass of dispersed phase to that of the continuous phase in a mixture.

**Quality :**

**Phase Loading :**

**Disperse Flows :**

**Dense Flows :**

*Collisions between the particles control the overall flow features.*

**Collision dominated :***Continuous particle to particle contact controls the overall flow features.*

**Contact dominated :****Stokes Number :**

**Significance of Stokes Number :**

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