View source for Physics:Coalescence

{{Short description|Merging of droplets, bubbles or particles}}
[[File:Coalescence.svg|thumb|200px|Representation of the coalescence of two droplets, bubbles, or particles to form a single entity.]]

'''Coalescence''' is the process by which two or more droplets, bubbles, or particles merge during contact to form a single daughter droplet, bubble, or particle. Coalescence manifests itself from a microscopic scale in [[Physics:Meteorology|meteorology]] to a macroscopic scale in [[Physics:Astrophysics|astrophysics]]. For example, it is seen in the formation of raindrops as well as planetary and [[Astronomy:Star formation|star formation]].

In meteorology, its role is crucial in the formation of rain.  As droplets are carried by the updrafts and downdrafts in a cloud, they collide and coalesce to form larger droplets.  When the droplets become too large to be sustained on the air currents, they begin to fall as rain.  Adding to this process, the cloud may be seeded with ice from higher altitudes, either via the cloud tops reaching {{convert|-40|C}}, or via the cloud being seeded by ice from [[Earth:Cirrus cloud|cirrus cloud]]s.

[[Biology:Contrast-enhanced ultrasound|Contrast-enhanced ultrasound]] in [[Medicine:Medicine|medicine]] applies microscopic [[Physics:Bubble|bubbles]] for [[Imaging|imaging]] and [[Chemistry:Therapy|therapy]]. Coalescence of [[Physics:Ultrasound|ultrasound]] contrast agent microbubbles is studied to prevent embolies<ref>{{cite journal | year=2004 | vauthors=Postema M, Marmottant P, Lancée CT, Hilgenfeldt S, de Jong N | title=Ultrasound-induced microbubble coalescence | journal=Ultrasound in Medicine & Biology | volume=30 | issue=10 | pages=1337–1344 | doi=10.1016/j.ultrasmedbio.2004.08.008 | pmid=15582233 | url=https://dx.doi.org/10.1016/j.ultrasmedbio.2004.08.008 }}</ref> or to block tumour vessels.<ref>{{cite journal | year=2010 | vauthors=Kotopoulis S, Postema M | title=Microfoam formation in a capillary | journal=Ultrasonics | volume=50 | issue=2 | pages=260–268 | doi=10.1016/j.ultras.2009.09.028 | pmid=19875143 | url=https://dx.doi.org/10.1016/j.ultras.2009.09.028}}</ref> Microbubble coalescence has been studied with the aid of [[Physics:High-speed photography|high-speed photography]].<ref>{{cite journal|date=2023|volume=9|issue=1|pages=37-40|journal=Current Directions in Biomedical Engineering|url=https://www.degruyter.com/document/doi/10.1515/cdbme-2023-1010/html|doi=10.1515/cdbme-2023-1010|title=Sonic cracking of calcium carbonate-encapsulated microbubbles observed at moderate acoustic amplitudes|vauthors=Poortinga AT, Postema M, Carlson CS, Anderton N, Yamasaku M, Otake N,  Kudo N|doi-access=free}}</ref>

In [[Physics:Cloud physics|cloud physics]] the main mechanism of collision is the different [[Physics:Terminal velocity|terminal velocity]]  between the droplets. The terminal velocity is a function of the droplet size. The other factors that determine the collision rate are the droplet concentration and [[Physics:Turbulence|turbulence]].<ref>{{Cite journal | doi=10.1029/2011JD016603|title = Turbulent effects on the microphysics and initiation of warm rain in deep convective clouds: 2-D simulations by a spectral mixed-phase microphysics cloud model| journal=Journal of Geophysical Research: Atmospheres| volume=117|year = 2012|vauthors = Benmoshe N, Pinsky M, Pokrovsky A, Khain, A|issue = D06|pages = D06220|bibcode = 2012JGRD..117.6220B| doi-access=free}}</ref>

==See also==
*[[Physics:Accretion (astrophysics)|Accretion (astrophysics)]]
*[[Astronomy:Accretion (meteorology)|Accretion (meteorology)]]
*Bergeron process
*[[Chemistry:Coalescer|Coalescer]]

==References==
<references />

==External links==
* [http://glossary.ametsoc.org/wiki/Coalescence American Meteorological Society, Glossary of Meteorology: Coalescence]
* [http://www.glossary.oilfield.slb.com/Display.cfm?Term=coalescence Schlumberger Oilfield Glossary] {{Webarchive|url=https://web.archive.org/web/20120531083640/http://www.glossary.oilfield.slb.com/Display.cfm?Term=coalescence |date=2012-05-31 }}
* [http://weather.cod.edu/sirvatka/bergeron.html The Bergeron Process]
* The Coalescence of Bubbles - A Numerical Study - {{webarchive |url=https://web.archive.org/web/20110401042426/http://www.ann.jussieu.fr/~frey/papers/coalescence/Chen%20L.,%20The%20coalescence%20of%20bubbles%20-%20a%20numerical%20study.pdf |archive-date=2011-04-01 }}

[[Category:Cloud and fog physics]]



{{Sourceattribution|Coalescence (physics)|1}}