Maro Publications

Cavitation

Notes

*6/15/2012

Maro Topics

Comments

Patents with Abstracts

Grinding

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Notes

“Cavitation is the formation and then immediate implosion of cavities in a liquid – i.e. small liquid-free zones ("bubbles") – that are the consequence of forces acting upon the liquid.[1] It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low.

Cavitation is a significant cause of wear in some engineering contexts. When entering high pressure areas, cavitation bubbles that implode on a metal surface cause cyclic stress. This results in surface fatigue of the metal causing a type of wear also called "cavitation". The most common examples of this kind of wear are pump impellers and bends when a sudden change in the direction of liquid occurs. Cavitation is usually divided into two classes of behaviour: inertial (or transient) cavitation and non-inertial cavitation.

Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Inertial cavitation occurs in nature in the strikes of mantis shrimps and pistol shrimps, as well as in the vascular tissues of plants. In man-made objects, it can occur in control valves, pumps, propellers and impellers.

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. Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers, etc.

Since the shock waves formed by cavitation are strong enough to significantly damage moving parts, cavitation is usually an undesirable phenomenon. It is 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”

“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 super-hard or tough 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.

Hydrophobic chemicals are attracted underwater by cavitation as the pressure difference between the bubbles and the liquid water forces them to join together. This effect may assist in protein folding.

(Wikipedia, Cavitation, 6/15/2012)

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“MHC provides cavitation by transmitting energy from rotating one or more rotor assemblies. One or more inline impeller-driven resonators with geometry optimized to induce violent inertial cavitation to disintegrate and reduce particles size of targeted particles disposed within a liquid. Liquids that are subjected to pressures below the liquid's saturated vapor pressure can overcome the liquid's intermolecular forces of cohesion and form cavities. These cavities, or cavitation bubbles, nearly instantly collapse due to the higher pressure of the surrounding liquid. This releases a significant amount of energy in the form of heat and an acoustic shock wave. Temperatures up to and exceeding 5,000 degrees Kelvin and pressures up to and exceeding 50 atmospheres give rise to the disintegration effect noted above. The effectiveness of cavitation increases with the presence of increased concentrations of smaller suspended solids because cavitation bubbles generally need a surface upon which they can nucleate. The output of FD is a large number of very small corn-mix particles that collectively provide a very large surface area and may enhance the productivity of MHC. MHC relies on mechanical and hydrodynamic phenomena to rapidly and cost-effectively generate highly energetic cavitation to disintegrate targeted biomass for nominal electricity (and carbon intensity) in a compact, continuous flow inline process.” [Kreisler and Winsness, US Patent 8,191,806 (6/5/2012)]

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Interested!!
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(RDC 6/5/2012)

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Roger D. Corneliussen
Editor
www.maropolymeronline.com

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Tel: 610 363 9920
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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 6/15/2012.