multiphase

Multiphase refers to systems that contain more than one distinct phase, where a phase is a region with uniform chemical composition and physical properties separated by interfaces. In thermodynamics, multiphase coexistence occurs when the system is at conditions (temperature and pressure) where two or more phases are thermodynamically stable; the Gibbs phase rule describes how many independent variables can be varied while keeping the number of phases fixed.

In fluid dynamics, multiphase flow involves two or more immiscible or partly miscible fluids moving together, such as gas–liquid mixtures in pipelines, steam generation, bubble columns, or sediment-laden flows. These flows involve exchange of mass, momentum, and energy and present challenges for modeling due to complex interfaces and turbulence.

In materials science and geology, multiphase materials contain distinct solid phases, or rocks and magmas with crystals embedded in a melt. Examples include steel with pearlite or bainite, cement paste with hydration products, and sedimentary or igneous rocks containing mineral phases. Phase diagrams and microstructure analysis help predict processing outcomes and properties by describing which phases are stable under given conditions.

Measurement and modeling approaches for multiphase systems include characterization of phase fractions and interfaces using microscopy, X-ray diffraction, tomography, and spectroscopy. Computational methods encompass Eulerian–Eulerian models for multiphase flow, mixture models, and interface-tracking techniques such as level-set or volume-of-fluid methods.

Applications span energy, chemical processing, materials engineering, and environmental science. Key challenges involve predicting phase distributions, ensuring stability of dispersions, understanding interfacial heat and mass transfer, and managing the computational complexity of simulations.