Cavitational yield

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]. 

Tatake PA, Pandit AB (2002) Modeling and experimental investigation into cavity dynamics and cavitational yield Influences of dual frequency ultrasound sources. Chem Eng Sci 57 4987 1995... 

Feng R, Zhao Y, Zhu C, Mason TJ (2002) Enhancement of ultrasonic cavitation yield by multi-frequency sonication. Ultrason Sonochem 9 231-236... 

The operating parameters used in the experimental work for the optimization exercise include inlet pressure (1 1 kg/cm2), concentration of the controlling reactant species (oxidant i.e. KMnC>4 in this case with concentration varied in the range 0.2-0.5 mol/L per mol of the toluene), type of the orifice plate (without orifice plate, orifice plates of two different geometries). The optimized conditions as obtained in the study are inlet pressure of 3 kg/cm2, 0.4 mol/L of the oxidant (beyond these values, the increase in the cavitational yield is only marginal) and orifice plate with more number of holes (cavitational yield is maximum out of all the geometries considered in the work). 

No Reactants Product0 Cavitational yield in hydrodynamic cavitation reactor (g/J) Cavitational yield in acoustic cavitation reactor (g/J)... 

Sivakumar and Pandit [13] reported the use of hydrodynamic cavitation for decolorization of dye effluent stream. It has been observed that for same flow area, plate with larger number of small diameter holes gives higher extent of color removal as compared to the plate with smaller number of larger diameter holes. The observed results have been explained on the basis of frequency of turbulence for the two cases. The hydrodynamic cavitation reactor using multiple hole orifice plates has been found to give cavitational yields, which are two times higher than the best acoustic cavitation device (Dual frequency flow cell with capacity of 1.5 L). 

Table 7.3 Effect of slurry concentration and C02 flow rates, Orifice diameter on conversion and cavitation yield [46]...

A series of fundamental studies on sonochemistry by Feng Ruo and his collaborators has been undertaken over a number of years. Their studies have focused on how the parameters of an ultrasonic field, such as sound intensity, frequency, shape of wave, etc., affect the cavitation yield which was detected by different methods. 

The pulse cavitation peak phenomenon, where under an appropriate choice of the pulse width the cavitation yield reached an apparently maximum value, was first studied in a reverberating field [84,85], Frequencies of823-kHz and 1,7-MHz ultrasonic waves modulated by rectangular wave with an on off ratio of 1 1 and pulse width from 100 ps to 270 s were used to irradiate both an aqueous terephtha-late solution and deionized water, respectively. After sonication, the fluorescence and electroconductivity changes of the samples were measured. All the experimental data showed that a maximum value of cavitation yield occurred in the pulse width range between 10 and 100 ms. The theoretical result predicted by the authors based on the sonicated system resonance with the modulation envelope appeared to be in agreement with experimental data. In further investigations a similar phenomenon was observed for the 1.7-MHz ultrasound modulated by sine wave [86,87],... 

As also mentioned in the previous section, hydrodynamic cavitation creates on average an order of magnitude higher cavitation yields than the acoustic cavitation. In... 

The above equation uses the collapse pressure in units of atmospheres, while the cavitational yield is predicted in terms of g/J. The proportionality constant for the equation depends on the concentration of KI and the time of the treatment. It can... 

It is worthwhile at this stage to compare the predictions of the cavitational yield from the obtained relationship with some of the earlier studies on decomposition of potassium iodide. Naidu et al. (1994) have studied the decomposition of potassium iodide in an ultrasonic bath having a cross-sectional area of 0.0404m and a height of 15 cm. The operating parameters used in the experimentation were 25 kHz driving frequency and 0.6188W/cm intensity. The results obtained indicate a linear variation in the iodine liberation with the initial concentration of potassium iodide and time of the reaction, which confirms the consideration of inclusion of the concentration of the reactant (i.e. KI in this case) and the reaction time in the proportionality constant. 

The data set obtained with the local measurements of cavitational yield for the Weissler reaction (Gogate et al., 2002) in the case of an ultrasonic bath can be effectively used for the development of the design equation for cavitational yield in terms of the maximum size of the cavity (recommended when free-radical attack is the controlling mechanism). The mathematical equation relating the two can be given as follows ... 

The equation is valid for acoustic pressure amplitude in the range of 2 to 7atm and an operating frequency of 22 kHz. More details about the equation in terms of measurement of cavitational yield and calculation of the Rmax/Ro ratio from numerical simulations have been given in the earlier work of Gogate et al. (2002). 

The second parameter that has been used for the characterization of the cavitational reactors is the cavitational yield that is given by the following correlation ... 

Cavitational Yield Results Table 8.2.4 also gives the values of cavitational yields obtained for different equipments for the Weissler reaction, ft can be seen from the table that a triple-frequency flow cell gives 2 to 3 orders of magnitude higher cavitational yield as compared to all the other equipments. A dual-frequency flow cell also gives 20% higher yield as compared to an ultrasonic bath, whereas the... 

Table 8.2.4 Comparison of cavitational equipments in terms of cavitational yields.

Thus, it can be said that multiple-transducer and/or multiple-frequency irradiation also results in an enhancement in the cavitational yield and these types of reactors should play a key role in the design of industrial-scale reactors. Another key feature of the flow cells is the possibility of continuous operation, which is another key requirement for the industrial-scale operation. 

Development of Correlations for Cavitational Yield A second step in the engineering design protocol is to develop design equations for the quantification of the net cavitational effects. We now highlight a simple methodology in terms of cavitational yield (quantification of chemical effects) for a model reaction. Gogate... 

The above equation requires the collapse pressure values in terms of atmospheres, whereas the cavitational yield value is given in units of g/(J/ml). The value of the proportionality constant is dependent on the concentration of K1 and the time of the reaction. 

Comparison of Cavitational Yields in Acoustic and Hydrodynamic Cavitation... 

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