What are the Factors that Affect Ultrasonic Cavitation?

When the pressure of the sound wave propagated by ultrasonic vibration in liquid reaches one atmosphere, the peak pressure of the ultrasonic wave can reach vacuum or negative pressure. However, in reality, there is no negative pressure present, so a large force is generated in the liquid, which pulls the liquid molecules into voids. This cavity is very close to vacuum, and it ruptures when the ultrasonic pressure reaches its maximum reverse direction. The strong impact generated by the rupture hits the dirt on the surface of the object. The shock wave phenomenon generated by the rupture of countless small cavitation bubbles is called the "cavitation" phenomenon.

The strength of ultrasonic cavitation is related to acoustic parameters and the physical and chemical properties of the liquid.

Ultrasonic intensity
Ultrasonic intensity refers to the ultrasonic power per unit area, and the generation of cavitation is related to the ultrasonic intensity. When the ultrasonic intensity of general liquids increases, the cavitation intensity increases, but after reaching a certain value, cavitation tends to saturate. At this point, increasing the ultrasonic intensity again will produce a large number of useless bubbles, thereby increasing scattering attenuation and reducing cavitation intensity.

Ultrasonic frequency
The lower the ultrasonic frequency, the easier it is to generate cavitation in the liquid. That is to say, to cause cavitation, the higher the frequency, the greater the required sound intensity. For example, to generate cavitation in water, the power required for ultrasonic frequency at 400kHz is 10 times greater than that at 10kHz, indicating that cavitation decreases with increasing frequency. The commonly used frequency range is 20-40kHz.

Surface tension and viscosity coefficient of liquids
The greater the surface tension of the liquid, the higher the cavitation intensity, and the less likely it is to generate cavitation. Liquids with high viscosity coefficients are difficult to generate cavitation bubbles, and the losses during propagation are also significant, so they are also less prone to cavitation.

Temperature of liquid
The higher the temperature of the liquid, the more favorable it is for the generation of cavitation. However, when the temperature is too high, the vapor pressure in the bubbles increases, thus enhancing the buffering effect and weakening cavitation when the bubbles close.