If ultrasound frequency projected to room humidifier that produce moisture by the help of ultrasound, the water evaporate when it was exposed to a vibrating metal diaphragm functioned by ultrasonic waves.
Attenuation is what causes heat to build up in a medium as sound passes through it. Water does not attenuate sound very well, so heats build up is very slow. Cavitations at the surface of an ultrasound transducer is easily produced and it looks like boiling, but it you put your hand in the mist, you will find it cold, not hot.
Occupational exposure to ultrasound in excess of 120 dB may lead to hearing loss. Exposure in excess of 155 dB may produce heating effects that are harmful to the human body, and it has been calculated that exposures above 180 dB may lead to death.
The UK’s independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA).
This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above.
Some industries use an ultrasonic cleaner at work (chirp spread spectrum of 2-33k). The water with wetting agent (a very dilute detergent) gets very hot. They don’t use it with just distilled water as the instruction manual advises not to.
If you do you will find that the cleaning action will be VERY abrasive. So abrasive can ablate away the stainless steel the tank is made out of.
Ultrasound does not boil at its own. But, it creates very rapid agitation in the liquid which leads to increase in kinetic energy creating rapid collisions and hence releases energy in the form of heat.
The heat starts heating up the liquid. And if Ultrasound is provided long enough, it may start boiling water. But there are good chances that our liquid will boil off below its normal boiling point because application of Ultrasound increases surface area of the liquid hence increased interracial area between atmosphere and liquid, which triggers natural convective evaporation to higher extent as rate of heat transfer is proportional to interface area.
Furthermore it generates bubbles due to intense pressures of waves which when collapses at the surface ejects tiny droplets which are in liquid phase but small enough to get airborne. Like mist.
US Navy subs analyzing and studying sound data suggest that when the electronics was upgraded on the spherical sonar system on these boats it was said on max power active it could boil water 3 feet from the transducers.
Thank you for reading.
Steve Ramsey. Calgary – Alberta – Canada