Collapsing bubble

The behavior of materials, particularly steel, in cavitating fluids results in an erosion mechanism, including mechanical erosion and electrochemical corrosion. The straightforward way to fight cavitation is to use hardened materials, chromium, chrome-nickel compounds, or elastomeric plastics. Other cures are to reduce the vapor pressure with additives, reduce the turbulence, change the liquid s temperature, or add air to act as a cushion for the collapsing bubbles. 

Suslick KS, Flannigan DJ (2008) Inside a collapsing bubble Sonoluminescence and the conditions during cavitation. Ann Rev Phys Chem 59 659-683... 

The nature of the dissolved gas i.e. its polytropic constant (y), solubility in the cavitating medium etc. severely affects the cavitational activity due to its direct effect on the final collapse conditions. The magnitude of temperature reached at the collapse is affected by the amount of gas dissolved in the liquid medium. Final temperature reached by the adiabatically collapsing bubble (mainly depends on polytropic coefficient of the gas (y)) can be given by following mathematical relationship ... 

Indirect oxidation by attack of OH radicals formed in bulk solution or interface between the collapsing bubbles (Reactions 11.5 and 11.6)... 

Two mechanisms have been proposed to explain how nonvolatile species become heated in a collapsing bubble [33, 34] (1) an interfacial liquid layer around the hot cavitation bubble is heated. The metal ions in the initially liquid layer are reduced... 

Fig. 7. Theoretical surface profiles of collapsing bubble near a boundary. Initially, the distance of the bubble s edge from the boundary was Rq/2. [After E. A. Neppiras (26).]...

Static pressure Total applied pressure Gas solubility Intensity of collapse Bubble content... 

Any system involving a homogeneous liquid in which bubbles are produced is not strictly homogeneous however in sonochemistry it is normal to consider the state of the system to which the ultrasound is applied. Sonochemical effects generally occur either inside the collapsing bubble where extreme conditions are produced, at the interface between the cavity and the bulk liquid where the conditions are far less extreme or in the bulk liquid immediately surrounding the bubble where the predominant effects will be mechanical (Fig. 3.2). 

Fixed volumes of original solution and of collapsed foams were taken with a micro (overflow type) pipet and transferred to respective sample plates which were coated partly with silicone oil to prevent wetting. The solution was dried gradually with infrared ray lamp and then radioactive counts were determined. On the other hand, the concentration of the solution of collapsed bubbles was determined by weighing. The accuracy of this method was confirmed by drying the solution of known concentration at respective experiments. The loss of acetic acid... 

Sonochemical reactions are strongly affected by ambient gas because the temperature inside the collapsing bubble is in close relationship with the polytropic ratio (Cp/C ) and the thermal conductivity of the gas. In addition, reactions with gases such as Oz, N2, and C02 are directly affected by the high temperatures reached during the collapse of the bubbles. As a consequence, reactive species available for PCP degradation and their rate of production will depend on the nature of the gas. 

Flint and Suslick (1991) and Seghal and Wang (1989) clearly demonstrated that temperature and pressure within a collapsing cavitation bubble exceed the critical point of water, on the basis of previously estimated temperatures within a collapsed bubble and a smaller layer of surrounding liquid. However, no experimental data are available for the density of nuclei or actual cavitation bubbles in water during ultrasonic irradiation or SCW accelerated chemical reactions. 

Colussi AJ, Hoffmann MR. Vapor supersaturation in collapsing bubbles. Relevance to the mechanisms of sonochemistry and sonoluminescence. J Phys Chem A 1999 103 11336-11339. 

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