Cavitation defined

Cavitation may be defined as the instantaneous formation and collapse of vapor bubbles in a liquid subject to rapid, intense localized pressure changes. Cavitation damage refers to the deterioration of a material resulting from its exposure to a cavitating fluid. 

The cavitation performance depends, to a large extent, on the conditions at the pump inlet or suction. These are defined by the parameter net positive suction head (NPSH) ... 

Fig. 31. Bubble wall velocity vs time during cavitational collapse for different values of the parameter X defined as X ss 0.4 c iTl] p./fri/2 (Ph — Pv)i/2). X permits us to account for the viscous and inertia effects of the polymer solution (redrawn according to Ref. [122]) ...

A second problem in these studies concerns cavitation dynamics on the nanometer length scale [86]. If sufficiently energetic, the ultrafast laser excitation of a gold nanoparticle causes strong nonequilibrium heating of the particle lattice and of the water shell close to the particle surface. Above a threshold in the laser power, which defines the onset of homogeneous nucleation, nanoscale water bubbles develop around the particles, expand, and collapse again within the first nanosecond after excitation (Fig. 9). The size of the bubbles may be examined in this way. 

In Fig. 1.1, the parameter space for transient and stable cavitation bubbles is shown in R0 (ambient bubble radius) - pa (acoustic amplitude) plane [15]. The ambient bubble radius is defined as the bubble radius when an acoustic wave (ultrasound) is absent. The acoustic amplitude is defined as the pressure amplitude of an acoustic wave (ultrasound). Here, transient and stable cavitation bubbles are defined by their shape stability. This is the result of numerical simulations of bubble pulsations. Above the thickest line, bubbles are those of transient cavitation. Below the thickest line, bubbles are those of stable cavitation. Near the left upper side, there is a region for bubbles of high-energy stable cavitation designated by Stable (strong nf0) . In the brackets, the type of acoustic cavitation noise is indicated. The acoustic cavitation noise is defined as acoustic emissions from... 

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...

A primary limitation of sonochemistry remains its energy inefficiency. This may be dramatically improved, however, if a more efficient means of coupling the sound field with preformed cavities can be found. The question of selectivity in and control of sonochemical reactions, as with any thermal process, remains a legitimate concern. There are, however, clearly defined means of controlling the conditions generated during cavitational collapse, which permit the variation of product distributions in a rational fashion. 

Strictly defined, cavitation refers only to the completely evacuated bubble or cavity, a true void, but since dissolved gases are present unless special steps are taken to remove them, and the vapor of the liquid can also penetrate the cavity, the term cavitation most often encompasses the three kinds of bubbles. 

Pumps shall operate within beating temperature hmits as defined in paragraph 2.9.2.3 and shall not display signs of unfavorable operation, such as noise caused by cavitation. 

Table 2. Summary of 3-buten-2-ol (3B20L) and 1,4-pentadien-3-ol (14PD30L) experiments are given. The abbreviations US and SS are defined as cavitating ultrasound and stirred/silent processing, respectively. The percent selectivity to final ketone plus saturated alcohol sum to 100%.

For instance, appreciable tensile strength had occasionally been noted in water tunnels (ref. 16). (The tensile strength of a liquid is defined here as the minimum tensile stress in the liquid at which it ruptures or cavitates (ref. 57).) The inception of cavitation in these water tunnels has occurred at higher stress levels than ordinarily expected. Higher flow velocities or lower tunnel pressures than normal have been needed to produce cavitation about a test body. The tensile strength acts as if an additional static head were present in the system. In this case, appreciable tensile strength is undesirable in order to make for a uniformity of test results, and duplicate prototype conditions (ref. 16). 

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