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

meteorology Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agricultur ...

to a macroscopic scale in astrophysics. For example, it is seen in the formation of raindrops as well as planetary and star formation. In meteorology, its role is crucial in the formation of

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

. 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 , or via the cloud being seeded by ice from cirrus clouds. Contrast-enhanced ultrasound in

medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

applies microscopic bubbles for imaging and therapy. Coalescence of

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

contrast agent microbubbles is studied to prevent embolies or to block tumour vessels. Microbubble coalescence has been studied with the aid of high-speed photography. In cloud physics the main mechanism of collision is the different 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 turbulence.

References

External links

American Meteorological Society, Glossary of Meteorology: Coalescence

Schlumberger Oilfield Glossary

* 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 Cloud and fog physics

See also

References

External links