Whistle Reactor

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. 

Chand et al. [64] have investigated the use of ozone treatment assisted by a liquid whistle reactor (LWR), which generates hydrodynamic cavitation, for water disinfection using a simulated effluent containing Escherichia coli. A suspension having an E. coli concentration of approximately 10s to 109 CFU mL 1 was introduced into the LWR to examine the effect of hydrodynamic cavitation alone... 

Chand R, Bremner DH, Namkung KC, Collier PJ, Gogate PR (2007) Water disinfection using a novel approach of ozone assisted liquid whistle reactor. Biochem Eng J 35 357-364... 

The practising chemist has four types of laboratory ultrasonic apparatus which are commercially available. One of these, the whistle reactor, relies on mechanical generation of ultrasonic power whereas the other three - the bath, probe and cup-horn systems - are driven by electromechanical transducers. The construction of such systems is discussed below and a summary of their relative advantages (and disadvantages) in sonochemical usage are summarised in Tab. 7.1. 

Of the four types of laboratory ultrasonic apparatus commercially available for practising chemists in general (namely, whistle reactors, ultrasonic cleaning baths, probes and cup-horn devices) analytical chemists, except for a few specialists working in (or with) ultrasound detectors, use mainly cleaning baths and probes both of which are usually operated at a fixed frequency dependent on the particular type of transducer, that is usually 20 kHz for common probe systems and 40 kHz for baths. Both types of devices are described below. 

There are numerous different types of equipment available for use as sonochemical reactors. The initial source of ultrasound comes from transducer devices which convert alternating electrical impulses to mechanical vibrations. Generally these are constructed of either piezoelectric or magnetostrictive material (p. 5). A purely mechanical low-frequency emitter is the whistle system, not frequently used by sonochemists, but of widespread usage in food processing (p. 311). Several set-ups are used to produce low-frequency ultrasoimd, from the simple cleaning baths to much more sophisticated emitters, sometimes using two... 

Ultrasound is currently employed in the preparation of emulsions on an industrial scale. In this case, the reagents are pumped through a minisonic homogenizer or whistle reactor (Fig. 17). Cavitation occurs as the fluid flows across a vibrating plate and the power obtainable is limited by this factor. Most of the chemical effects observed arise from the vast increase in interfacial area rather than the ultrasonic irradiation itself. However, its advantages stem from its proven ability to process large quantities of material in this manner. 

Fig. 17. Commercially available minisonic homogeniser, or whistle reactor...

See section on "Whistle reactors" (Section 2.4) which are already in commercial use for making paint etc. 

In addition, overseas professional practice is also informative to study e.g. the Tokyo Electric Power Company (TEPCO), which had nuclear reactor problems arising after the 2011 tsunami. A later investigation revealed that a senior field engineer, who was dismissed some years prior for whistle-blowing, had alerted TEPCO to problems with their nuclear reactors several years ago (Moret 2011). 

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