written by: Andrew E
• edited by: Swagatam
• updated: 9/15/2008
When cavitation occurs it can sometimes be very destructive. However, when done in a controlled environment, it can be helpful.
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You may already know what causes cavitation and how to avoid it, but what exactly does it do? There is no denying that it causes damage, but it also has helpful uses. As long as we understand its effects, that power can be harnessed for good things.
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Damage to Pipes
Prolonged cavitation in pipes can lead to severe problems. If left unattended, the results of cavitation can be disastrous, as it eats away at the pipe and creates vibrations that will cause the pipe to fail. If you have ever had or seen a pipe fail, it is not pretty. Fluid sprays everywhere and requires requires a lot more clean up than just replacing a pipe.
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Cavitation can be a culprit in the erosion of river banks and coastlines. It cannot be considered the only cause of erosion, as much of the erosion we see is based on water wearing down and washing away small pieces of the land. However, cavitation can speed up the degradation of the area. In beach erosion, waves can force air bubbles into cracks already in the rock which become compressed with the force of the wave. This causes cavitation within the crack that can, in effect, break off large chunks of rock.
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Cavitation damage on propellers is a large concern in the design of high speed propellers. A general rule is that the faster the propeller spins, the higher your speed. However, a higher speed means a greater chance of cavitation. The cavitation usually occurs at the trailing end of each blade of the propeller. Designers have to come up with new propeller shapes that reduce the the possibility of cavitation so that higher speeds can be achieved.
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Despite the damage that cavitation can do, it can be harnessed for useful applications. Chemical mixing by cavitation is sometimes used when particles need to be broken down within a liquid in order to spread efficiently throughout the mixture. This is generally accomplished by forcing the mixture through a small orifice that turns into a very large orifice, thus causing cavitation to occur at that point.
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The other way that cavitation can be useful is when it is induced through ultrasonic vibration. Anyone who has suffered from a kidney stone will tell you how painful it is and a kidney stone that will not pass will get you an appointment to have them broken down. The process used to break up a kidney stone is usually done with ultrasonic waves that uses cavitation as well as the shockwave themselves to break apart the stone.
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Ultrasound induced cavitation, also known as non-inertial cavitation, is also used is the cleaning of sensitive materials. This is a form of cavitation that can be controlled and tends to be less damaging than pressure induced cavitation. For cleaning, the cavitation bubbles form on the surface of the object and can knock off small particles that are missed by manual cleaning.