Cavitation can be defined as the formation and collapsing of vapor-filled bubbles in a liquid due to a drop in static pressure. It happens when the pressure of fluid falls below the vapor pressure.
Cavitation can lead to wear and tear in some engineering scenarios. For example, when cavitation occurs in a metal container, and the bubbles explode next to the surface of the container repeatedly, it will lead to gradual corrosion of the container and might affect the efficiency of a machine.
Related: ultrasonic cavitation machines
Types of Cavitation Machines
Although all cavitation devices utilize ultrasound waves to cause fat loss, there are different types of cavitation slimming systems on the market.
Based on the number of wands or heads each machine has, there are 3 in 1, 4 in 1, 5 in 1, 7 in 1 cavitation machines, and so on. For example, 3 in 1 ultrasonic cavitation machines come with an ultrasound cavitation wand, a multi-polar radio frequency (RF) wand, and a tri-polar RF wand. 4 in 1 ultrasonic cavitation machines offer the same devices as a 3-in-1 model, plus a bipolar or tripolar radiofrequency instrument to treat lines and wrinkles on the face.
Besides, based on the frequency, cavitation machines can also be classified into 40K cavitation machines, 60K cavitation machines, 80K cavitation machines, etc. The selection depends on your own needs and skin type.
More to Know About Cavitation
Types of Cavitation
1. Vaporous Cavitation
This type of cavitation occurs when the static pressure in a part of a flowing liquid drops to a level lower than the saturated vapor pressure of the fluid. This leads to the formation of vapor bubbles. These bubbles collapse almost immediately when the static pressure rises above the fluid’s vapor pressure.
The process of formation and implosion of the vapor bubbles is swift. The implosion of the bubbles takes place at the speed of sound. During the implosion process, shock waves, light, heat, and noise are released due to the high pressures within the bubbles.
Due to the speed and continuity of implosion of bubbles, the container holding the fluid is subjected to gradual corrosion. As a result, cavitation can drastically affect performance and longevity.
Vaporous cavitation is also referred to as cavitation wear, liquid impact erosion, cavitation erosion, and cavitation fatigue. It can be observed in propeller blades, pumps, impellers, pipes, etc.
2. Gaseous Cavitation
Gaseous cavitation is the process of diffusion of gas into a liquid when the static pressure of the gas falls lower than its saturation pressure in the fluid. This means that the liquid can contain minute amounts of dissolved gas, and the quantity of gas dissolved in the liquid can increase or decrease depending on changes in temperature and pressure.
Gaseous cavitation can further be explained by Henry’s Law, which states that “the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.”
In other words, the amount of gas in a given liquid will continue to increase as more gas dissolves until the liquid reaches a balance between the pressure in the liquid and the partial pressure of the gas.
If the liquid undergoes frequent changes in pressure and temperature, the amount of gas dissolved in it will frequently adjust to maintain the balance within the system.
Gaseous cavitation occurs more slowly than vaporous cavitation. The speed of gaseous cavitation depends on the speed of circulation in the fluid.
The process of gaseous cavitation produces a lot of noise and very high temperatures and causes decomposition of the liquid via oxidation.
Unlike vaporous cavitation, gaseous cavitation does not cause cavitation wear. Cavitation wear can only occur when shock waves and microjets cause corrosion of surfaces. Hence gaseous cavitation cannot cause cavitation wear.
Cavitation wear is a type of corrosion/wear caused by the impact of a fluid colliding with a solid surface. The surface is usually a metal used in machinery. Cavitation wear cannot take place in the absence of a liquid.
Cavitation wear causes wear and tear of machines and components of machines. Over an extended period, cavitation wear can cause the collapse of a machine or one of its parts due to repeated erosion of its surface.
The process starts with the formation of cavities at low pressures. Then, as the pressure stabilizes, bubbles are formed. Finally, as the pressure gradually increases, the bubbles implode with impact on close-by surfaces.
This pressure of this impact is what causes the corrosion of the surface. In addition, the higher the frequency of implosion of bubbles, the faster the surface corrodes. Eventually, the implosion pressure leads to the formation of microcracks on the machine’s surface.
These micro-cracks lead to bits of the machine breaking off from the body with time. These bits are introduced to the system, and the device reduces strength and efficacy.
Cavitation wear is more likely to occur if the surface is rough. Smoother surfaces are less likely to be affected. However, after continuous pressure and impact, even smooth surfaces are bound to start having micro-cracks that eventually break off, creating a rough surface.
The rougher the surface, the faster corrosion will occur. Hence, once cavitation wear starts, it is a downhill ride.
How to Reduce Cavitation Wear
There are several ways to prevent or reduce cavitation wear. The materials used in machinery construction are an essential factor to consider when minimizing the damage caused by cavitation wear.
For instance, construction engineers may use stainless steel instead of using aluminum or copper to increase durability. Also, engineers may use rubber or plastic to coat surfaces to reduce cavitation.
Engineers may also use micro-bubble deaerators to prevent gaseous cavitation.