What is ultrasound cavitation, sometimes called ? It is a natural process where ultrasonic cavitation liposuction are either intentionally, or as the byproduct of some other mechanical process, aimed at a liquid. The result is what is known as cavitation. This is where, in the liquid, a vacuum is produced in between the liquid’s molecules, forming millions upon millions of microscopic bubbles. Now, I’ve already talked about ultrasonic liposuction. Today I want to talk about an industrial application of cavitation, called ultrasonic cleaning. This application is the use of UC as a cleaning process. The microscopic bubbles produced in cavitation have the effect of cleaning any parts which are submerged in the liquid in which they form. These bubbles are extremely small, and extremely short-lived. 10′s of thousands of these little vacuum bubbles are produced in every square milliliter of the liquid in question every second. At the microscopic level, temperatures near the bubbles can reach up to 10,000 degrees Celsius, and the pressure produced near the bubbles can go as high 10,000 PSI. Each time one of these tiny, short-lived bubbles forms and rubs against the surface of a part in an industrial setting, contaminants are removed and the part is gently cleaned.
How Are Bubbles Produced in Ultrasound Cavitation?
The number of bubbles produced per second, and the distribution of these bubbles, is regulated by the exact frequency of the ultrasonic waves in use. For instance, at 80khz, 80,000 bubbles are produced locally every second. When developing a cleaning process, it is important to understand the nature of the part that will be cleaned, and to “tweak” the frequency to be sure and get the right strength of cleaning, while avoiding dead spots caused by standing waves.
It’s important to understand how sound waves are produced and how they act in order to understand ultrasound waves and, hence, ultrasound (or ultrasonic) cavitation. Sounds waves, like ultrasonic waves, have 2 parts of their cycle. The first is a cycle of expansion in which they move apart. This compression cycle is what caused the liquid in an ultrasound cavitation machine to form bubbles. The second part of the cycle is the compression cycle. In this phase, the sound wave retracts, causing the bubbles formed to compress and to burst.
Basically, when understanding how frequency affects the rate at which bubbles form and burst, it’s important to see that with a higher frequency comes a shorter cycle time. The expansion/compression cycles are shorter, producing smaller bubbles, or cavities, What’s more, in talking about the cleaning action of ultrasonic cavitation, know that higher frequencies result in a more gentle cleaning action due to the smaller size and shorter life of the cavities.
Other variables that can affect ultrasonic cavitation are:
- Movement of the Fluid
- If the fluid is moving, the cleaning action is drastically reduced. To help mitigate the affects of fluid motion, when it can’t be avoided, you can raise the ultrasonic frequency, use a smaller tank, or employ a greater watt/gallon density.
- Dissolved Gasses
- Dissolved gasses serve to buffer the bubbles, or cavities, almost as a type of microscopic “shock absorber”. If dissolved gasses are present to any large degree in the cleaning liquid, you should de-gas the liquid before or during cavitation. This can sometimes give a gain of up to 50% greater cleaning.
- Design the Basket or Tank Appropriately
- Typically, tanks used for ultrasound cavitation are comprised of wire mesh. This material is fine, but several factors, including the size of the mesh, the material used for the basket, and the shape of the basket. The basket should be open, the mesh size should not be too fine, and plastic should never be used as a material.
Make sense? I hope you enjoyed reading this primer on the use of ultrasonic cavitation in cleaning applications as much as I enjoyed writing it.
