Indeed, this also has implications for calorimetry, what is considered by
some sonochemists to be the standard way of measuring the ultrasonic power.
You estimate the ultrasonic power from the temperature rise the ultrasound
produces in the liquid. But if the temperature rises, the sound speed rises,
and the frequency at which a specific mode occurs changes. Hence the
act of making a calorimetric measurement can completely change the
sonochemical efficiency of the system.
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For example, for every 1°C rise in water temperature, the percentage change in the frequency f at which a given mode occurs is df/f= 0.3 %.
Typically during calorimetry the liquid temperature rises by ~3°C (i.e. df/f~1%).
The video opposite shows what happens when one changes the driving frequency by only 0.5%: one moves into and out of a mode, and the luminescence changes dramatically.
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For the
homepage of the Centre Ultrasonics and Underwater Acoustics (UAUA),
click © T G Leighton 2004
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