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1 Cavitation and Chemical Reactivity
1.6 Parameters Influencing the Sonochemical Activity
It is generally accepted that the number of parameters exerting a possible influence
on the fate of cavitation is relatively important. However, it is also commonly agreed
that only a few of them exert a quantifiable impact, whose are summarized hereafter.
1.6.1 Ultrasonic Frequency
Frequency and intensity of the ultrasonic wave are obviously the two essential components of an ultrasonic wave. The frequency (f ) of a sound wave is defined as c/λ
where c is the celerity of sound (m/s) and λ the wavelength (m). Whereas a 20 kHz
frequency displays a wavelength of 74 mm in water, this value is around 3 mm
at 500 kHz. This difference in acoustic cycles numbers within the same period in
between these two frequencies leads to a different dynamic behaviour of cavitation
bubbles and certainly issue of whether transient or stable cavitation.
1.6.2 Acoustic Intensity
The intensity of a sound wave can be defined as the power carried per surface and
can be expressed as follows:
I P
2
A
2ρc
(1.2)
where P A is the acoustic pressure amplitude of the sound wave, ρ is the density of
the medium and c is the celerity of sound in the medium.
However, this formula remains valid only for planar or spherical progressive waves
with low-pressure variations. In the case of low-frequency ultrasound, variations of
acoustic pressure may reach up to a few bars leading to a complex and non-linear
acoustic system (Lepoint and Lepoint-Mullié 1998). When speaking about intensity,
sonochemists do refer preferentially to the acoustic power delivered to the liquid
medium by the ultrasonic device.
1.6.3 Temperature
Unsurprisingly, temperature exerts a great importance in sonochemistry. Regardless
of the ultrasonic wave itself, the maximum cavitation efficiency will rely mainly
on a good balance of several solvent’s properties like viscosity, volatility and density. Thus, the bubbles’ dynamic will be inherently affected by the changes induced
1 Cavitation and Chemical Reactivity
1.6 Parameters Influencing the Sonochemical Activity
It is generally accepted that the number of parameters exerting a possible influence
on the fate of cavitation is relatively important. However, it is also commonly agreed
that only a few of them exert a quantifiable impact, whose are summarized hereafter.
1.6.1 Ultrasonic Frequency
Frequency and intensity of the ultrasonic wave are obviously the two essential components of an ultrasonic wave. The frequency (f ) of a sound wave is defined as c/λ
where c is the celerity of sound (m/s) and λ the wavelength (m). Whereas a 20 kHz
frequency displays a wavelength of 74 mm in water, this value is around 3 mm
at 500 kHz. This difference in acoustic cycles numbers within the same period in
between these two frequencies leads to a different dynamic behaviour of cavitation
bubbles and certainly issue of whether transient or stable cavitation.
1.6.2 Acoustic Intensity
The intensity of a sound wave can be defined as the power carried per surface and
can be expressed as follows:
I P
2
A
2ρc
(1.2)
where P A is the acoustic pressure amplitude of the sound wave, ρ is the density of
the medium and c is the celerity of sound in the medium.
However, this formula remains valid only for planar or spherical progressive waves
with low-pressure variations. In the case of low-frequency ultrasound, variations of
acoustic pressure may reach up to a few bars leading to a complex and non-linear
acoustic system (Lepoint and Lepoint-Mullié 1998). When speaking about intensity,
sonochemists do refer preferentially to the acoustic power delivered to the liquid
medium by the ultrasonic device.
1.6.3 Temperature
Unsurprisingly, temperature exerts a great importance in sonochemistry. Regardless
of the ultrasonic wave itself, the maximum cavitation efficiency will rely mainly
on a good balance of several solvent’s properties like viscosity, volatility and density. Thus, the bubbles’ dynamic will be inherently affected by the changes induced