Editing Two-phase flow (section)

== Characteristics of two-phase flow ==
Several features make two-phase flow an interesting and challenging branch of fluid mechanics:

*[[Surface tension]] makes all dynamical problems [[nonlinear]] (see [[Weber number]])
*In the case of air and water at [[standard temperature and pressure]], the [[density]] of the two phases differs by a factor of about 1000. Similar differences are typical of water liquid/water vapor densities
*The sound speed changes dramatically for materials undergoing phase change, and can be orders of magnitude different. This introduces [[compressible]] effects into the problem
*The phase changes are not instantaneous, and the liquid vapor system will not necessarily be in phase equilibrium
*The change of phase means flow-induced pressure drops can cause further phase-change (e.g. water can evaporate through a valve) increasing the relative volume of the gaseous, compressible medium and increasing exit velocities, unlike single-phase incompressible flow where closing a valve would decrease exit velocities
*Can give rise to other counter-intuitive, negative resistance-type instabilities, like [[Ledinegg instability]], [[geyser]]ing, [[Rocket engine#Combustion instabilities|chugging]], [[relaxation instability]], and flow maldistribution instabilities as examples of ''static'' instabilities, and other ''dynamic'' instabilities<ref>Ghiaasiaan, S. M.Two-Phase Flow, Boiling, and Condensation: In Conventional and Miniature Systems, Cambridge University Press, 2008. pg 362.</ref>
Additional exhaustive information, like applied mathematical models can be found in. <ref>{{Cite book |last=Ishi |first=M. |title=Thermo-Fluid Dynamics of Two-Phase Flow |last2=Hibiki |first2=T. |publisher=Springer |year=2006 |isbn=9780387283210}}</ref><ref>{{Cite book |last=Peker |first=S. M. |title=Solid–Liquid Two Phase Flow |last2=Helvaci |first2=S.S. |publisher=Elsevier |year=2008 |isbn=978-0-444-52237-5}}</ref><ref>{{Cite book |last=Gross |first=S. |title=Numerical Methods for Two-phase Incompressible Flows |last2=Reusken |first2=A. |publisher=Springer |year=2011 |isbn=978-3-642-19685-0}}</ref><ref>{{Cite journal |last=Stewart |first=H.B. |last2=Wendroff |first2=H. |date=1984 |title=Two-phase flow: models and methods |url=https://www.sciencedirect.com/science/article/abs/pii/0021999184901037 |journal=Journal of Computational Physics |volume=56 |pages=363 |doi=10.1016/0021-9991(84)90103-7|url-access=subscription }}</ref><ref>{{Cite journal |last=Tiselj |first=I. |last2=Petelin |first2=S. |date=1997 |title=Modeling of two-phase flow with second-order accurate scheme |url=https://www.sciencedirect.com/science/article/abs/pii/S0021999197957788 |journal=Journal of Computational Physics |volume=136 |issue=2 |pages=503-521 |doi=10.1006/jcph.1997.5778|url-access=subscription }}</ref>