Cavitation hydrodynamic

The schematic in Fig. 3 shows that the synthesis starts with one solution or more containing the metal salts, such as nitrates, acetates, alkoxides, and chlorides. If the solutions are not compatible, the metal ions must be fed using multiple-feed streams. This stream is metered into a second stream containing a precipitating agent such as sodium hydroxide, ammonium hydroxide, or ammonium or sodium carbonate. Care is taken to ensure that the individual metal salts totally and immediately precipitate upon contacting 

BUBBLE COLLAPSE SHOCK WAVE MORE SHEAR MORE PARTICLE SHEAR 

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Vibratory test apparatuses are relatively cheap to build and run, and have low power consumption, while flow rigs are bulky, expensive to build and run, and have high power consumptions but have the advantage that they simulate more closely practical conditions of hydrodynamic cavitation. On the other hand, the damage rate is higher in the vibratory tests than in the... 

Purposeful hydrodynamic cavitation in a chemical reactor can be created in two ways. One alternative is to let the hquid pass through a throttling valve, orifice... 

Hydrodynamic cavitation reactors have been investigated for more than a decade now in the UDCT Department of Bombay University [63-66]. When applied to some industrially relevant reactions, the hydrodynamically created cavitation appeared to dehver on average an order of magnitude higher cavitation yields than the acoustic cavitation. In addition, the processing volumes could be up to about 100 times larger than in the conventional sonochemical reactors. So far, there is no information about the industrial applications of the hydrodynamic cavitation reactors, although some concepts have already been patented [67]. 

Pandit and co-workers have shown that scale-up may be possible on a more rational basis if cavitation is employed, and some data have been reported by Pandit and Mohalkar (1996), Mohalkar et al. (1999), Senthil et al. (1999), and Cains et al. (1998). A variety of reactors can be used, viz. the liquid whistle reactor, the Branson sonochemical reactor, the Pote reactor, etc. The principal factors affecting the efficiency of a hydrodynamic cavitation reactor are irreversible loss in pressure head and turbulence and friction losses in the reaction rates. 

MiUy, P. J., Toledo, R. T., Chen, J., and Kazem, B. (2007). Hydrodynamic cavitation to improve bulk fluid to surface mass transfer in a nonimmersed ultraviolet system for minimal processing of opaque and transparent fluid foods. /. Food Sci. 72, M407-M413. 

In acoustic cavitation, some bubbles dramatically expand and violently collapse, which is called the inertial collapse or Rayleigh collapse. It is caused by both the spherically shrinking geometry and the inertia of the surrounding liquid which inwardly flows into the bubble. The bubble collapse is similar to that in hydrodynamic cavitation which is induced by a sudden drop of pressure below the saturated vapor pressure due to a fluid flow through an orifice [92, 93]. At the end of the... 

Wang X, Zhang Y (2009) Degradation of alachlor in aqueous solution by using hydrodynamic cavitation. J Fiaz Mater 161 202-207... 

It can be said that acoustic and hydrodynamic cavitation are the result of the tensions prevailing in a liquid, while optic and particle cavitation are the consequence of the local deposition of energy. The classification scheme for the phenomena of cavitation has been shown schematically in Fig. 2.1. Once the cavities are generated, subsequent expansion of the minute cavity may be achieved by reducing the ambient pressure using static or dynamic means. The surrounding... 

Cavitation Generation and Usage Without Ultrasound Hydrodynamic Cavitation... 

Hydrodynamic cavitation, which generates similar effects as the well established acoustic cavitation, has long being known for its detrimental effects and tackled accordingly. Literature dating back to late nineteenth century report the destruction caused by cavitation in speed boats. English navy, in an attempt to make high... 

Fig. 3.1 Fluid flow and Pressure variation in hydrodynamic cavitation set-up...

Acoustic cavitation is as a result of the passage of ultrasound through the medium, while hydrodynamic cavitation occurs as the result of the velocity variation in the flow due to the changing geometry of the path of fluid flow. In spite of this difference in the mechanisms of generation of two types of cavitation, bubble behavior shows similar trends with the variation of parameters in both these types of cavitation. The two main aspects of bubble behavior in cavitation phenomena are ... 

Moholkar et al. [11] studied the effect of operating parameters, viz. recovery pressure and time of recovery in the case of hydrodynamic cavitation reactors and the frequency and intensity of irradiation in the case of acoustic cavitation reactors, on the cavity behavior. From their study, it can be seen that the increase in the frequency of irradiation and reduction in the time of the pressure recovery result in an increment in the lifetime of the cavity, whereas amplitude of cavity oscillations increases with an increase in the intensity of ultrasonic irradiation and the recovery pressure and the rate of pressure recovery. Thus, it can be said that the intensity of ultrasound in the case of acoustic cavitation and the recovery pressure in the case of hydrodynamic cavitation are analogous to each other. Similarly, the frequency of the ultrasound and the time or rate of pressure recovery, are analogous to each other. Thus, it is clear that hydrodynamic cavitation can also be used for carrying out so called sonochemical transformations and the desired/sufficient cavitation intensities can be obtained using proper geometric and operating conditions. 

Several reports appear in literature confirming that hydrodynamic cavitation is more energy efficient than acoustic cavitation [12-14], Higher energy effectiveness of hydrodynamic cavitation can be mainly attributed to following two factors ... 

It is always important to choose an optimum design configuration of the hydrodynamic cavitation reactor so as to maximize the cavitational effects and achieve cost effective operation. In this section, we will discuss available reactor configurations and give some guidelines, based on theoretical analysis coupled with experimental results, for selection of optimum design and operating parameters for hydrodynamic cavitation reactors. 

From the above discussion about various hydrodynamic cavitation reactors, it can be easily concluded that the orifice plate set-up offers maximum flexibility and can also be operated at relatively larger scales of operation. It should be also noted that the scale-up of such reactors is relatively easier as the efficiency of the pump increases with an increase in size (flow rate and discharge pressure) which will necessarily result into higher energy efficiencies. 

Guidelines for Selection of Hydrodynamic Cavitation Reactor Configurations... 

Table 3.1 Optimum operating conditions for the hydrodynamic cavitation reactors No. Property Favorable conditions...

Ambulgekar et al. [30] investigated the oxidation of toluene using aqueous KMn04 as an oxidizing agent in the hydrodynamic cavitation reactor with an objective of optimization of the operating parameters. The reaction scheme can be depicted as follows ... 

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