It is very often specifically avoided in the design of machines such as turbines or propellers, and eliminating cavitation is a major field in the study of fluid dynamics. Since the shock waves formed by collapse of the voids are strong enough to cause significant damage to parts, cavitation is typically an undesirable phenomenon in machinery (although desirable if intentionally used, for example, to sterilize contaminated surgical instruments, break down pollutants in water purification systems, emulsify tissue for cataract surgery or kidney stone lithotripsy, or homogenize fluids). Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers, etc.
Non-inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. In man-made objects, it can occur in control valves, pumps, propellers and impellers. Inertial cavitation occurs in nature in the strikes of mantis shrimps and pistol shrimps, as well as in the vascular tissues of plants. The process in which a void or bubble in a liquid rapidly collapses, producing a shock wave, is called inertial cavitation. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation and non-inertial cavitation. The most common examples of this kind of wear are to pump impellers, and bends where a sudden change in the direction of liquid occurs. This results in surface fatigue of the metal causing a type of wear also called "cavitation". Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion. These shock waves are strong when they are very close to the imploded bubble, but rapidly weaken as they propagate away from the implosion.Ĭavitation is a significant cause of wear in some engineering contexts.
When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery. Bronze propeller on river barge with an anti-cavitation plate above the prop.Ĭavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid.
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