Multiphase flow
Encyclopedia
In fluid mechanics
, multiphase flow is a generalisation of the modelling used in two-phase flow to cases where the two phases are not chemically related (e.g. dusty gases) or where more than two phases are present (e.g. in modelling of propagating steam explosion
s).
Each of the phase
s is considered to have a separately defined volume fraction (the sum of which is unity), and velocity field.
Conservation equations
for the flow of each species (perhaps with terms for interchange between the phases), can then be written down straightforwardly.
The momentum equation for each phase is less straightforward. It can be shown that a common pressure
field can be defined, and that each phase is subject to the gradient of this field, weighted by its volume fraction. Transfer of momentum between the phases is sometimes less straightforward to determine, and in addition, a very light phase in bubble form has a virtual mass
associated with its acceleration. (The virtual mass of a single bubble is about half its displaced mass).
These terms, often called constitutive relation
s, are often strongly dependent on flow regime
Fluid mechanics
Fluid mechanics is the study of fluids and the forces on them. Fluid mechanics can be divided into fluid statics, the study of fluids at rest; fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of forces on fluid motion...
, multiphase flow is a generalisation of the modelling used in two-phase flow to cases where the two phases are not chemically related (e.g. dusty gases) or where more than two phases are present (e.g. in modelling of propagating steam explosion
Steam explosion
A steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or the interaction of molten metals A steam explosion (also called a littoral explosion, or fuel-coolant interaction, FCI) is a...
s).
Each of the phase
Phase (matter)
In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...
s is considered to have a separately defined volume fraction (the sum of which is unity), and velocity field.
Conservation equations
Continuity equation
A continuity equation in physics is a differential equation that describes the transport of a conserved quantity. Since mass, energy, momentum, electric charge and other natural quantities are conserved under their respective appropriate conditions, a variety of physical phenomena may be described...
for the flow of each species (perhaps with terms for interchange between the phases), can then be written down straightforwardly.
The momentum equation for each phase is less straightforward. It can be shown that a common pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
field can be defined, and that each phase is subject to the gradient of this field, weighted by its volume fraction. Transfer of momentum between the phases is sometimes less straightforward to determine, and in addition, a very light phase in bubble form has a virtual mass
Added mass
In fluid mechanics, added mass or virtual mass is the inertia added to a system because an accelerating or decelerating body must move some volume of surrounding fluid as it moves through it, since the object and fluid cannot occupy the same physical space simultaneously...
associated with its acceleration. (The virtual mass of a single bubble is about half its displaced mass).
These terms, often called constitutive relation
Constitutive equation
In physics, a constitutive equation is a relation between two physical quantities that is specific to a material or substance, and approximates the response of that material to external forces...
s, are often strongly dependent on flow regime
See also
- Two-phase flow
- Buckley–Leverett equationBuckley–Leverett equationIn fluid dynamics, the Buckley–Leverett equation is a transport equation used to model two-phase flow in porous media. The Buckley–Leverett equation or the Buckley–Leverett displacement can be interpreted as a way of incorporating the microscopic effects to due capillary pressure in two-phase flow...
- Darcy's law for multiphase flow in porous media.
- Multiphase flow meterMultiphase flow meterA multiphase flow meter is a device used in the oil and gas industry to measure the individual phase flow rates of petroleum, water and gas mixtures produced during oil production processes.- Background :...
- three phase flow meter
- Multiphase Heat TransferMultiphase heat transfer-Definitions:A multiphase system is one characterized by the simultaneous presence of several phases, the two-phase system being the simplest case. The term ‘two-component’ is sometimes used to describe flows in which the phases consist of different chemical substances. For example, steam-water...