What is Multiphase Flow

As a general definition - Two or more phases flowing simultaneously in a closed conduit is referred to as Multiphase Flow.

Multiphase flows are the most common flow occurrences in nature. Examples are the flow of blood in the human body, the bubbles rising in a glass of cold beer and the steam condensation on windows.

The simplest case of multiphase flow is -  of a two-phase flow in which the same pure component is present in two different phases. An example - a steam-water flow.

On the other hand, if different chemical substances co-exist, the flow is usually referred to as multicomponent. This is the case of an air–water flow (two-phases, two components).

Multiphase measurement is a catch of all term that describes multiple fluid components in a flowing stream. For instance, water and oil are considered to be multiphase in the oil and gas industry, even though they are both liquids.

The phases present in a multiphase flow are composed of:

1. Solids, which are normally in the form of relatively small particles. The solid phase is incompressible and has non-deformable interfaces with the surrounding fluids.
2. Liquids, which are also relatively incompressible, but their interfaces with the other phases are deformable.
3. Gases, where the phase is compressible and deformable

Some common class of two phase multiphase flows are -

• Gas–solid flows - solid particles are suspended in gases.
• Liquid–liquids flows -  emulsion flows of oil and water in pipelines.
• Liquid–solid flows - Suspensions of solids in liquids.
• Gas–liquid flows - Gas flowing with oil and/or water

Three-phase flows examples being as follows -

• Gas–liquid–solid flows - found in froth flotation as a means of separating minerals.
• Gas–liquid–liquid flows -  oil, water and natural gas.
• Solid–liquid–liquid flows - occur if sand was mixed with oil and water in the pipeline

The four-phase flow example can be - a oil–water–gas–sand mixture

The types of multiphase flow which are of interest foe the Oil and Gas Industry are -

• gas–liquid flows (oil–natural gas), 
• liquid–liquid flows (oil–water), 
• gas–liquid–liquid flows (natural gas–oil–water) and 
• solid–liquid–liquid–gas flows (sand–oil–water–natural gas)..

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