1.8 Guidelines for Adequate Use of Ultrasonic Devices
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• Never place a reaction vessel directly in contact with the bottom emitting wall
of the water tank but tightly and adequately suspended in the tank.
• Better to use a flat-bottom vessel than a round-bottom one to maximize surface
exposure of the vessel to ultrasonic waves.
• The level of the liquid inside the reaction vessel should be more or less at
the same height than the level of water filling the cleaning bath to maximize
surfacing mechanical effects.
Precepts for horn systems:
• Check the integrity of the horn tip immersed into the reaction vessel. If the tip
is badly damaged, it must be changed to avoid metal contamination and loss of
acoustical power.
• A damaged tip can be sanded and polished but with possible risk of probe
detuning and lower deliverable cavitation intensity.
• Reaction vessel must be thermostatically controlled prior (to avoid unwished
side effects due to the sudden rise in temperature such vaporous cavitation,
enhanced degassing effect, overheating, etc.) and during the experiment.
• Position the emitting horn not too close from the bottom of the vessel to avoid
reflection which may dramatically damage the ultrasonic horn and not too close
from the liquid level to avoid cushioning effects with ambient gas and to minimize dead zones.
• Homogenize a solid/liquid heterogeneous solution by adding gradually the solid
and a liquid/liquid solution by placing the horn just above the liquid/liquid
interface to literally ‘push’ one liquid into another one.
• A round-bottom flask is preferred than a flat one for a better dispersion of
ultrasonic waves throughout the vessel and to prevent reflection of the sound
waves leading to the overheating of the probe.
• Pressurized reactions with horn systems are possible but be sure that the horn
and the set-up are connected at the null (or nodal) point of the probe to avoid
probe damages and overheating.
Precepts for ‘cup-horn’ systems at high frequency:
• The height of the liquid column submitted to ultrasonic waves is of importance
(de La Rochebrochard et al. 2012). This parameter, which is often obscured
because it is difficult to apprehend, is nevertheless crucial for a maximum and
homogeneous distribution of the acoustic energy across the ultrasonic reactor.
This optimization can be achieved with adequate chemical dosimeters introduced in the next paragraph.
• Heavily heterogeneous systems must not be submitted to high-frequency ‘cuphorn’ systems as solids will depose at the bottom of the reactor where is located
the ceramic resulting in high reflection of ultrasonic waves and breakage of the
ceramic.
• Pressurized reactions are barely possible with high-frequency ‘cup-horn’ systems notably in reason of the fragility of the ceramics and reached weak power
levels of ultrasound.
11
• Never place a reaction vessel directly in contact with the bottom emitting wall
of the water tank but tightly and adequately suspended in the tank.
• Better to use a flat-bottom vessel than a round-bottom one to maximize surface
exposure of the vessel to ultrasonic waves.
• The level of the liquid inside the reaction vessel should be more or less at
the same height than the level of water filling the cleaning bath to maximize
surfacing mechanical effects.
Precepts for horn systems:
• Check the integrity of the horn tip immersed into the reaction vessel. If the tip
is badly damaged, it must be changed to avoid metal contamination and loss of
acoustical power.
• A damaged tip can be sanded and polished but with possible risk of probe
detuning and lower deliverable cavitation intensity.
• Reaction vessel must be thermostatically controlled prior (to avoid unwished
side effects due to the sudden rise in temperature such vaporous cavitation,
enhanced degassing effect, overheating, etc.) and during the experiment.
• Position the emitting horn not too close from the bottom of the vessel to avoid
reflection which may dramatically damage the ultrasonic horn and not too close
from the liquid level to avoid cushioning effects with ambient gas and to minimize dead zones.
• Homogenize a solid/liquid heterogeneous solution by adding gradually the solid
and a liquid/liquid solution by placing the horn just above the liquid/liquid
interface to literally ‘push’ one liquid into another one.
• A round-bottom flask is preferred than a flat one for a better dispersion of
ultrasonic waves throughout the vessel and to prevent reflection of the sound
waves leading to the overheating of the probe.
• Pressurized reactions with horn systems are possible but be sure that the horn
and the set-up are connected at the null (or nodal) point of the probe to avoid
probe damages and overheating.
Precepts for ‘cup-horn’ systems at high frequency:
• The height of the liquid column submitted to ultrasonic waves is of importance
(de La Rochebrochard et al. 2012). This parameter, which is often obscured
because it is difficult to apprehend, is nevertheless crucial for a maximum and
homogeneous distribution of the acoustic energy across the ultrasonic reactor.
This optimization can be achieved with adequate chemical dosimeters introduced in the next paragraph.
• Heavily heterogeneous systems must not be submitted to high-frequency ‘cuphorn’ systems as solids will depose at the bottom of the reactor where is located
the ceramic resulting in high reflection of ultrasonic waves and breakage of the
ceramic.
• Pressurized reactions are barely possible with high-frequency ‘cup-horn’ systems notably in reason of the fragility of the ceramics and reached weak power
levels of ultrasound.