Cavitation forces

Ultrasonic extraction is a well-known commercial method to increase mass transfer rate by cavitation forces. Bubbles in the liquid-solid extraction using UE can explosively collapse and produce localized pressure, improving the interaction between the intracellular substances and the solvent to facilitate the extraction of the phytochemical. 

Scenario Hydrofoils traveling at high rates of speed are damaged by the cavitational action of water on the hydrofoil. To prevent the destructive cavitational forces acting on the surface of the foil, a thin layer of ice is introduced by refrigerating the surface of the foil, thus forming a renewable... 

Wet Dispersion Wet dispersion separates agglomerates down to the primary particles by a suitable liquid. Dispersing agents and optional cavitational forces induced by ultrasound are often used. Care must be taken that the particles not be soluble in the liquid, or that they not flocculate. Microscopy and zeta potential measurements may be of utility in specifying the proper dispersing agents and conditions for dispersion. 

Patek SN, Caldwell RL (2005) Extreme impact and cavitation forces of a biological hammer strike forces of the peacock mantis shrimp Odontodactylus scyllarus. J Exp Biol 208 3655-3664... 

Fig. 20 Schematic diagram showing the lelatitmship between cavitational forces and cell siffface strength. Rigid structures are broken by bubble collapse, with little or no microstreaming effect. The a -axis strength factor, no numerical values are givtai) provides an indication on the shear forces required to dismpt mammalian or microbial cells. Reproduced with permission from...

The continuum models presented in previous sections are focused only on electrostatic effect which is accompanied by insertion of a solute in a solvent, namely the bulk polarization of the solvent by the field of the solute. However, all these models neglect some other physical effects [36]. Among them probably the most important are the dispersion and the cavitation forces. 

Some solutions may not be practical, or economical, or timely and consistent with production. You could be forced to live with cavitation until the next plant shutdown to make the neces.sary corrections. In the meantime, the cavitation shock waves and vibrations will travel through the impeller, down the shaft to the mechanical seal faces, and onto the shaft bearings. We offer some. specific recommendations for surviving cavitation shock waves and vibrations in Chapters 13 and 14 on Mechanical Seals. 

At higher flow rates cavitation is a serious degradation mechanism, where vapor bubbles created by pressure fluctuations brought about by the flow of liquid past the surface collapse on the metal surface with tremendous force. This damages any protective oxide which may be present, leading to pitting corrosion. It also causes mechanical damage to the metal. 

The alternative option for counteracting cavitation damage is the use of a resilient material such as rubber. The mechanical forces attendant on collapse of the bubbles are absorbed by elastic deformation of the resilient material. 

The process by which a material becomes eroded when exposed to the forces resulting from the collapse of cavitation bubbles proceeds in a number of stages according to Thiruvengadam and Preiser . In the first of these, the... 

Mettin R, Akhatov I, Parlitz U, Ohl CD, Lauterbom W (1997) Bjerknes forces between small cavitation bubbles in a strong acoustic field. Phys Rev E 56 2924—2931... 

For cavitation to occur in a liquid, it has to overcome the natural cohesive forces present in the liquid. Any increase in these forces will tend to increase the threshold pressure and hence the energy required to generate cavitation. In highly viscous liquids, severe attenuation of the sound intensity occurs and the active cavitating zone gets reduced substantially. Moholkar et al. [56] have confirmed this fact with experiments with different liquids and reported that for highly viscous liquids, cavitational effects are not observed. 

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