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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cavitation | 4/8 | https://en.wikipedia.org/wiki/Cavitation | reference | science, encyclopedia | 2026-05-05T10:54:45.984996+00:00 | kb-cron |
=== Acoustic cavitation and ultrasonic cavitation === Inertial cavitation can also occur in the presence of an acoustic field. Microscopic gas bubbles that are generally present in a liquid will be forced to oscillate due to an applied acoustic field. If the acoustic intensity is sufficiently high, the bubbles will first grow in size and then rapidly collapse. Hence, inertial cavitation can occur even if the rarefaction in the liquid is insufficient for a Rayleigh-like void to occur. Ultrasonic cavitation inception will occur when the acceleration of the ultrasound source is enough to produce the needed pressure drop. This pressure drop depends on the value of the acceleration and the size of the affected volume by the pressure wave. The dimensionless number that predicts ultrasonic cavitation is the Garcia-Atance number. High power ultrasonic horns produce accelerations high enough to create a cavitating region that can be used for homogenization, dispersion, deagglomeration, erosion, cleaning, milling, emulsification, extraction, disintegration, and sonochemistry.
== Applications ==
=== Water transport === In supercavitation, cavitation is intentionally induced around high-speed submerged objects to reduce skin drag.
=== Chemical engineering === In industry, cavitation is often used to homogenize, or mix and break down, suspended particles in a colloidal liquid compound such as paint mixtures or milk. Many industrial mixing machines are based upon this design principle. It is usually achieved through impeller design or by forcing the mixture through an annular opening that has a narrow entrance orifice with a much larger exit orifice. In the latter case, the drastic decrease in pressure as the liquid accelerates into a larger volume induces cavitation. This method can be controlled with hydraulic devices that control inlet orifice size, allowing for dynamic adjustment during the process, or modification for different substances. The surface of this type of mixing valve, against which surface the cavitation bubbles are driven causing their implosion, undergoes tremendous mechanical and thermal localized stress; they are therefore often constructed of extremely strong and hard materials such as stainless steel, Stellite, or even polycrystalline diamond (PCD). Cavitating water purification devices have also been designed, in which the extreme conditions of cavitation can break down pollutants and organic molecules. Spectral analysis of light emitted in sonochemical reactions reveal chemical and plasma-based mechanisms of energy transfer. The light emitted from cavitation bubbles is termed sonoluminescence. Use of this technology has been tried successfully in alkali refining of vegetable oils. Hydrophobic chemicals are attracted underwater by cavitation as the pressure difference between the bubbles and the liquid water forces them to join. This effect may assist in protein folding.
=== Biomedical === Cavitation plays an important role for the destruction of kidney stones in shock wave lithotripsy. Currently, tests are being conducted as to whether cavitation can be used to transfer large molecules into biological cells (sonoporation). Nitrogen cavitation is a method used in research to lyse cell membranes while leaving organelles intact. Cavitation plays a key role in non-thermal, non-invasive fractionation of tissue for treatment of a variety of diseases and can be used to open the blood-brain barrier to increase uptake of neurological drugs in the brain. Cavitation also plays a role in HIFU, a thermal non-invasive treatment methodology for cancer. In wounds caused by high velocity impacts (like for example bullet wounds) there are also effects due to cavitation. The exact wounding mechanisms are not completely understood yet as there is temporary cavitation, and permanent cavitation together with crushing, tearing and stretching. Also the high variance in density within the body makes it hard to determine its effects. Ultrasound sometimes is used to increase bone formation, for instance in post-surgical applications. It has been suggested that the sound of "cracking" knuckles derives from the collapse of cavitation in the synovial fluid within the joint. Cavitation can also form Ozone micro-nanobubbles which shows promise in dental applications.
=== Cleaning === In industrial cleaning applications, cavitation has sufficient power to overcome the particle-to-substrate adhesion forces, loosening contaminants. The threshold pressure required to initiate cavitation is a strong function of the pulse width and the power input. This method works by generating acoustic cavitation in the cleaning fluid, picking up and carrying contaminant particles away in the hope that they do not reattach to the material being cleaned (which is a possibility when the object is immersed, for example in an ultrasonic cleaning bath). The same physical forces that remove contaminants also have the potential to damage the target being cleaned.
=== Food and beverage ===
==== Eggs ==== Cavitation has been applied to egg pasteurization. A hole-filled rotor produces cavitation bubbles, heating the liquid from within. Equipment surfaces stay cooler than the passing liquid, so eggs do not harden as they did on the hot surfaces of older equipment. The intensity of cavitation can be adjusted, making it possible to tune the process for minimum protein damage.
==== Vegetable oil production ==== Cavitation has been applied to vegetable oil degumming and refining since 2011 and is considered a proven and standard technology in this application. The implementation of hydrodynamic cavitation in the degumming and refining process allows for a significant reduction in process aid, such as chemicals, water and bleaching clay, use.
=== Biofuels ===
==== Biodiesel ==== Cavitation has been applied to Biodiesel production since 2011 and is considered a proven and standard technology in this application. The implementation of hydrodynamic cavitation in the transesterification process allows for a significant reduction in catalyst use, quality improvement and production capacity increase.
== Cavitation damage ==