Number cavitation

Archimedes number Bingham number Bingham Reynolds number Blake number Bond number Capillary number Cauchy number Cavitation number Dean number Deborah number Drag coefficient Elasticity number Euler number Fanning friction factor Froude number Densometric Froude number Hedstrom number Hodgson number Mach number Newton number Ohnesorge number Peclet number Pipeline parameter... 

Increases in the appHed static pressure increase the acoustic intensity necessary for cavitation, but if equal number of cavitation events occur, the coUapse should be more intense. In contrast, as the ambient pressure is reduced, eventuaUy the gas-fiUed crevices of particulate matter which serve as nucleation sites for the formation of cavitation in even "pure" Hquids, wiU be deactivated, and therefore the observed sonochemistry wiU be diminished. 

Some attempts have been made to reslurry the filter cake without having to open the filter press. However, a number of problems appear, eg, bending of the plates due to uneven cake deposition or cavitation, uneven dewatering and washing within the frames, and plugging of the inlet ports. 

Collapse of vapor bubbles once they reach zones where the pressure exceeds the vapor pressure can cause objectionable noise and vibration and extensive erosion or pitting of the boundaiy materials. The critical cavitation number at inception of cavitation, denoted <7, is useful in correlating equipment performance data ... 

FIG. 6-55 Critical cavitation number vs. diameter ratio (3. Reprinted from Thotpe, Flow regime transitions due to cavitation in the flow through an orifice, " Int. J. Multiphase Flow, i6,1023-1045. Copyright 1990, with kindper-mission from Elsevier Science, Ltd., The Boulevard, Langford Lane, Kldlington 0X5 1GB, United Kingdom. )... 

The actual shape of the curve illustrated in Fig. 12.4 can vary according to factors such as metal properties and cavitation intensity. (Cavitation intensity relates to the number of bubbles created in a unit volume of fluid and the amount of energy transferred during the col-... 

For the centrifugal pump, two terms are in common use, the Thoma cavitation number cr and the suction specific speed Sn ... 

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... 

Rao et al. (R5) and Raju et al. (R2) also investigated mass transfer at vibrating electrodes for low vibration frequencies (higher frequencies would cause cavitation). Mass transfer follows a laminar-type correlation both for a transverse vibration of a vertical cylinder and for a vertical plate vibrating parallel to the face. In the case of the plate, the Reynolds number is based on width, indicating the predominance of form drag. When vibrations take place perpendicular to the thickness, skin friction predominates and the Reynolds number is then preferably based on the equivalent diameter (total surface area divided by transverse perimeter). 

Fig. 1.1 The regions for transient cavitation bubbles and stable cavitation bubbles when they are defined by the shape stability of bubbles in the parameter space of ambient bubble radius (R0) and the acoustic amplitude (p ). The ultrasonic frequency is 515 kHz. The thickest line is the border between the region for stable cavitation bubbles and that for transient ones. The type of bubble pulsation has been indicated by the frequency spectrum of acoustic cavitation noise such as nf0 (periodic pulsation with the acoustic period), nfo/2 (doubled acoustic period), nf0/4 (quadrupled acoustic period), and chaotic (non-periodic pulsation). Any transient cavitation bubbles result in the broad-band noise due to the temporal fluctuation in the number of bubbles. Reprinted from Ultrasonics Sonochemistry, vol. 17, K.Yasui, T.Tuziuti, J. Lee, T.Kozuka, A.Towata, and Y. Iida, Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles, pp. 460-472, Copyright (2010), with permission from Elsevier...

Relative importance of coalescence and rectified diffusion in the bubble growth is still under debate. After acoustic cavitation is fully started, coalescence of bubbles may be the main mechanism of the bubble growth [16, 34], On the other hand, at the initial development of acoustic cavitation, rectified diffusion may be the main mechanism as the rate of coalescence is proportional to the square of the number density of bubbles which should be small at the initial stage of acoustic cavitation. Further studies are required on this subject. 

Yasui K, Tuziuti T, Lee J, Kozuka T, Towata A, Iida Y (2010) Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles. Ultrason Sonochem 17 460-472... 

If the power dissipated into the system is increased, although the collapse pressure, as predicted using bubble dynamics analysis [14], decreases with an increase in the intensity, the number of cavitation events also increases (increase is substantial as compared to the negative effect of decreasing collapse pressure) thereby increasing the overall cavitational activity and hence enhanced effects can be observed. Usually the increase in number of cavities generated seizes after a... 

Formation of increased cavitation nuclei due to more number of discontinuities in liquid continuum as a result of the presence of particles to give larger number of collapse events resulting in increase in the number of free radicals. 

In the sonochemical reactors, selection of suitable operating parameters such as the intensity and the frequency of ultrasound and the vapor pressure of the cavitating media is an essential factor as the bubble behavior and hence the yields of sonochemical transformation are significantly altered due to these parameters. It is necessary that both the frequency and intensity of irradiation should not be increased beyond an optimum value, which is also a function of the type of the application and the equipment under consideration. The liquid phase physicochemical properties should be adjusted in such a way that generation of cavitation events is eased and also large number of smaller size cavities are formed in the system. 

A dimensionless number known as the cavitation number (Cv) has generally been used to relate the flow conditions with the cavitation intensity [8] ... 

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