12
1 Cavitation and Chemical Reactivity
The design of the ultrasonic reactor plays also a crucial role in the distribution
of the acoustic energy. Usually, reaction vessels incorporating curves lines are more
adequate for ultrasound than the ones bearing right angles as opened angles help to
scatter acoustic waves throughout the liquid medium. In addition, to further expand
towards sustainable development, the energetic consumption remains of high concern
in the world of sonochemistry with more or less optimized commercially available or
lab-made equipment. One way to reduce the energetic bill is to use pulsed ultrasound
instead of continuous one. The obvious output will be a decrease in the overall
energetic consumption of the reaction but also may reduce the cushioning effects of
the ineffective bubbles clouds. Silent periods can help to dissolve or to disperse out
these ineffective bubbles close to the irradiation source which leads to less energy
scattered by the bubbles. It is also important to endeavour a comparison between
ultrasonic-assisted and silent reactions with strictly same experimental conditions
apart from the activation method prior to claim any substantial effect of ultrasound.
Then, further investigation can be eventually undertaken to reveal the nature of and
to quantify the effects of ultrasound, i.e. physical and/or chemical origin. For that,
several chemical and physical methodologies or technologies have been designed.
1.9 Physical and Chemical Dosimetry Methods
to Quantify/Qualify Cavitation Activity
To elucidate a mechanism occurring under ultrasonic irradiation, a full characterization of the acoustic field is necessary. The determination of the ultrasonic energy
distribution throughout a reaction vessel is also of high interest for scalability to determine optimum operating parameters. Moreover, ultrasonic effects can be of either
physical or chemical nature emphasizing the complexity of measurements and above
all about their real significance. Physical and chemical effects can predominate or
coexist according to the incident ultrasonic frequency and the other aforementioned
operating parameters, making difficult the development of a single method. Several
chemical and physical dosimetry methods have been therefore designed to confront
critically results collected with different set-ups with standardized methodologies.
The most known and used are hereafter introduced with respective easiness to be
implemented.
1.9.1 Physical Methods
The acoustic pressure can be measured by calorimetry as the propagation of the
ultrasonic waves throughout the liquid medium provokes measurable heating phenomena (Kimura et al. 1996). The reaction vessel is here assimilated as a calorimeter
containing the mass of liquid (m) submitted to ultrasound. The rise of temperature
1 Cavitation and Chemical Reactivity
The design of the ultrasonic reactor plays also a crucial role in the distribution
of the acoustic energy. Usually, reaction vessels incorporating curves lines are more
adequate for ultrasound than the ones bearing right angles as opened angles help to
scatter acoustic waves throughout the liquid medium. In addition, to further expand
towards sustainable development, the energetic consumption remains of high concern
in the world of sonochemistry with more or less optimized commercially available or
lab-made equipment. One way to reduce the energetic bill is to use pulsed ultrasound
instead of continuous one. The obvious output will be a decrease in the overall
energetic consumption of the reaction but also may reduce the cushioning effects of
the ineffective bubbles clouds. Silent periods can help to dissolve or to disperse out
these ineffective bubbles close to the irradiation source which leads to less energy
scattered by the bubbles. It is also important to endeavour a comparison between
ultrasonic-assisted and silent reactions with strictly same experimental conditions
apart from the activation method prior to claim any substantial effect of ultrasound.
Then, further investigation can be eventually undertaken to reveal the nature of and
to quantify the effects of ultrasound, i.e. physical and/or chemical origin. For that,
several chemical and physical methodologies or technologies have been designed.
1.9 Physical and Chemical Dosimetry Methods
to Quantify/Qualify Cavitation Activity
To elucidate a mechanism occurring under ultrasonic irradiation, a full characterization of the acoustic field is necessary. The determination of the ultrasonic energy
distribution throughout a reaction vessel is also of high interest for scalability to determine optimum operating parameters. Moreover, ultrasonic effects can be of either
physical or chemical nature emphasizing the complexity of measurements and above
all about their real significance. Physical and chemical effects can predominate or
coexist according to the incident ultrasonic frequency and the other aforementioned
operating parameters, making difficult the development of a single method. Several
chemical and physical dosimetry methods have been therefore designed to confront
critically results collected with different set-ups with standardized methodologies.
The most known and used are hereafter introduced with respective easiness to be
implemented.
1.9.1 Physical Methods
The acoustic pressure can be measured by calorimetry as the propagation of the
ultrasonic waves throughout the liquid medium provokes measurable heating phenomena (Kimura et al. 1996). The reaction vessel is here assimilated as a calorimeter
containing the mass of liquid (m) submitted to ultrasound. The rise of temperature