Editing Cavitation (section)

=== Inertial cavitation ===
Inertial cavitation was first observed in the late 19th century, considering the collapse of a spherical void within a liquid. When a volume of liquid is subjected to a sufficiently low [[pressure]], it may rupture and form a cavity. This phenomenon is coined ''cavitation inception'' and may occur behind the blade of a rapidly rotating propeller or on any surface vibrating in the liquid with sufficient amplitude and acceleration. A fast-flowing river can cause cavitation on rock surfaces, particularly when there is a drop-off, such as on a waterfall.{{citation needed|date=July 2023|reason=are these holes in river water not just air bubbles at atmospheric pressure?}}

[[Vapor]] gases evaporate into the cavity from the surrounding medium; thus, the cavity is not a vacuum at all, but rather a low-pressure vapor (gas) bubble. Once the conditions which caused the bubble to form are no longer present, such as when the bubble moves downstream, the surrounding liquid begins to implode due its higher pressure, building up momentum as it moves inward. As the bubble finally collapses, the inward momentum of the surrounding liquid causes a sharp increase of pressure and temperature of the vapor within. The bubble eventually collapses to a minute fraction of its original size, at which point the gas within dissipates into the surrounding liquid via a rather violent mechanism which releases a significant amount of energy in the form of an acoustic shock wave and as [[sonoluminescence|visible light]]. At the point of total collapse, the temperature of the vapor within the bubble may be several thousand [[Kelvin]], and the pressure several hundred atmospheres.<ref>{{cite journal|journal=Environmental Health Perspectives|volume=64|pages=233–252|date=1985|title=Free radical generation by ultrasound in aqueous and nonaqueous solutions|last1=Riesz|first1=P.|first2=D.|last2=Berdahl|first3=C.L.|last3=Christman|pmc=1568618|doi=10.2307/3430013|pmid=3007091|jstor=3430013}}</ref>

The physical process of cavitation inception is similar to [[boiling]]. The major difference between the two is the [[thermodynamic]] paths that precede the formation of the vapor. Boiling occurs when the local temperature of the liquid reaches the [[saturation temperature]], and further heat is supplied to allow the liquid to sufficiently [[phase transition|phase change]] into a gas. Cavitation inception occurs when the local pressure falls sufficiently far below the saturated vapor pressure, a value given by the tensile strength of the liquid at a certain temperature.<ref>{{cite web|last1=Brennen|first1=Christopher |title=Cavitation and Bubble Dynamics|publisher=Oxford University Press|pages=21 |url=http://authors.library.caltech.edu/25017/1/cavbubdynam.pdf |archive-url=https://web.archive.org/web/20121004094948/http://authors.library.caltech.edu/25017/1/cavbubdynam.pdf |archive-date=2012-10-04 |url-status=live|access-date=27 February 2015}}</ref>

In order for cavitation inception to occur, the cavitation "bubbles" generally need a surface on which they can [[nucleation|nucleate]]. This surface can be provided by the sides of a container, by [[impurity|impurities]] in the liquid, or by small undissolved microbubbles within the liquid. It is generally accepted that [[hydrophobe|hydrophobic]] surfaces stabilize small bubbles. These pre-existing bubbles start to grow unbounded when they are exposed to a pressure below the threshold pressure, termed Blake's threshold.<ref>{{cite book|vauthors=Postema M, de Jong N, Schmitz G|title=IEEE Ultrasonics Symposium, 2005 |chapter=Shell rupture threshold, fragmentation threshold, blake threshold |date=Sep 2005|volume=3 |location=Rotterdam, Netherlands|pages=1708–1711|doi=10.1109/ULTSYM.2005.1603194|isbn=0-7803-9382-1 |s2cid=5683516 |chapter-url=https://hal.archives-ouvertes.fr/hal-03193373/document}}</ref> The presence of an incompressible core inside a cavitation nucleus substantially lowers the cavitation threshold below the Blake threshold.<ref>{{cite journal|vauthors=Carlson CS, Matsumoto R, Fushino K, Shinzato M, Kudo N, Postema M|title=Nucleation threshold of carbon black ultrasound contrast agent|journal=Japanese Journal of Applied Physics|year=2021|volume=60|issue=SD|pages=SDDA06|doi=10.35848/1347-4065/abef0f|bibcode=2021JaJAP..60DDA06C |s2cid=233539493 |url=https://hal.archives-ouvertes.fr/hal-03192654/document|doi-access=free}}</ref>

The vapor pressure here differs from the meteorological definition of vapor pressure, which describes the partial pressure of water in the atmosphere at some value less than 100% saturation. Vapor pressure as relating to cavitation refers to the vapor pressure in equilibrium conditions and can therefore be more accurately defined as the equilibrium (or saturated) [[vapor pressure]].

Non-inertial cavitation is the process in which small bubbles in a liquid are forced to oscillate in the presence of an acoustic field, when the intensity of the acoustic field is insufficient to cause total bubble collapse. This form of cavitation causes significantly less erosion than inertial cavitation, and is often used for the cleaning of delicate materials, such as [[silicon wafer]]s.

Other ways of generating cavitation voids involve the local deposition of energy, such as an intense focused laser pulse (optic cavitation) or with an electrical discharge through a spark. These techniques have been used to study the evolution of the bubble that is actually created by locally boiling the liquid with a local increment of temperature.