Influence of liquid-surface vibration on sonochemiluminescence intensity

The influence of surface vibrations on the intensity of sonochemiluminescence (SCL) produced by pulsed ultrasound with a frequency of 151 kHz is investigated through optical measurement of the vibration amplitude. Pulsed ultrasound inhibits the generation of large degassing bubbles that scatter sound waves, thereby restricting the effective spatial region for sonochemical reactions. The vibration amplitude of the liquid surface becomes gradually significant with pulsed ultrasound as the power applied to the transducer increases. At this time, the SCL intensity increases and then decreases after displaying a peak because the resonance of standing wave cannot be maintained stably by the surface vibration. The SCL intensity during high-amplitude pulsing becomes almost zero if the distance between the highest position of the liquid surface and its position in the absence of ultrasound becomes close to larger than one-quarter of the ultrasound wavelength. This condition for the liquid surface vibration provides a limit for establishment of a resonant standing wave that is effective for sonochemical reaction. Adding particles provides nucleation sites for cavitation bubbles, thereby inhibiting the vibration of the surface of the upper liquid level. The SCL intensity is enhanced by the addition of alumina particles under pulsed excitation at relatively low applied powers.