Hydrodynamic cavitation sonochemical reactor

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. 

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. 

Kanthale PM, Gogate PR, Wilhelm AM, Pandit AB (2005) Dynamics of cavitational bubbles and design of a hydrodynamic cavitational reactor cluster approach. Ultrason Sonochem 12 441 -52... 

Combination of the hydrodynamic-cavitation reactors and sonochemical reactors where the cavity is generated using the hydrodynamic means and the collapse of the cavities is taking place in the sonochemical reactor. The distance between the two events (generation and collapse) will be a crucial design aspect in the expected synergism and should be established with theoretical simulations and/or experimental validation for a particular application. The developed reactor should be operated in a continuous mode and needs be tested for different cavitational transformations. 

The reactor used for the sonochemical work was a conventional ultrasonic bath that many readers will recognise as a piece of equipment for cleaning components. The hydrodynamic cavitation reactor was a vessel with an orifice plate in the main feed line to generate cavitation. While fully acceptable yields of 97-99% were achieved with the sonochemical reactor (and also, except for the case of peanut oil feedstock, with the hydrodynanuc cavitation reactor), the most interesting data related to the energy used. These are compared in Table 8.4. The energy efficiency is defined as the yield in kg of product per kJ of energy used in the reactor. 

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