Multiphase flow

In fluid mechanics, multiphase flow is the simultaneous flow of materials with two or more thermodynamic phases. These phases may consist of one chemical component (e. g. flow of water and water vapour), or several different chemical components (e. g. flow of oil and water). A phase is classified as continuous if it occupies a continually connected region of space (as opposed to disperse if the phase occupies disconnected regions of space). The continuous phase may be either gaseous or a liquid. The disperse phase can consist of a solid, liquid or gas. Two general topologies can be identified: disperse flows and separated flows. The former consists of finite particles, drops or bubbles distributed within a continuous phase, whereas the latter consists of two or more continuous streams of fluids separated by interfaces. In the mid 20th century, advances in nucleate boiling were developed and the first two phase pressure drop models were formed, primarily for the chemical and process industries. In particular, Lockhart and Martinelli (1949) presented a model for frictional pressure drop in horizontal, separated two phase flow, introducing a parameter that is still utilised today. Between 1950 and 1960, intensive work in the aerospace and nuclear sectors triggered further studies into two phase flow. In 1958 one of the earliest systematic studies of two phase flow was undertaken by Soviet scientist Teletov. Baker (1965) conducted studies into vertical flow regimes. From the 1970s onwards, multiphase flow especially in the context of the oil industry has been studied extensively due to the increasing dependence of petroleum by the world economy. The 1980s saw further modelling of multiphase flow by modelling flow patterns to different pipe inclinations and diameters and different pressures and flows. Advancements in computing power in the 1990s allowed for increasingly complex modelling techniques to modelling multiphase flow, flows that were previously limited to one dimensional problems could be pushed to three dimensional models.

Multiphase flow occurs regularly in many natural phenomena, and also is well documented and crucial within various industries.

Sediment transport in rivers is subject to multiphase flow, in which the suspended particles are treated as a disperse second phase which interacts with the continuous fluid phase. An example of multiphase flow on a smaller scale would be within porous structures. Pore structure modelling enables the use Darcy's law to calculate the volumetric flow rate through porous media such as groundwater flow through rock. Further examples occur within the bodies of living organisms, such as blood flow (with plasma being the liquid phase and red blood cells constituting the solid phase. Also flow within the intestinal tract of the human body, with solid food particles and water flowing simultaneously.

The large majority of processing technology involves multiphase flow. A common example of multiphase flow in industry is a fluidized bed. This device combines a solid liquid mixture and causes it to move like a fluid. Further examples include water electrolysis, bubbly flow in nuclear reactors, gas particle flow in combustion reactors and fiber suspension flows within the pulp and paper industry. In oil and gas industries, multiphase flow often implies to simultaneous flow of oil, water and gas. The term is also applicable to the properties of a flow in some field where there is a chemical injection or various types of inhibitors. In petroleum engineering, drilling fluid consists of a gas solid phase. Furthermore, crude oil during flow through pipelines is a gas oil water three phase flow.