What is Ultrasonic Degassing?

 

Introduction to ultrasonic degassing:

 

Ultrasonic degassing is the process of removing dissolved gases and/or entrained small bubbles from a liquid. Gases removed from various liquids, including water, candle wax, polymer, epoxy resin, silicone oil, adhesives, coatings, beverages, inks, coatings, transformer oil, lotion and suspension products, engine oil, etc. Degassing can significantly improve the quality of the final product (reducing defects, improving aesthetics, etc.), unlike vacuum degassing using intermittent methods, ultrasonic degassing can be carried out in continuous flow mode.

 

 

Operational Principle:

 

Ultrasound propagates from a sound transmitter to a liquid medium, producing alternating positive and negative pressure phases. In the negative pressure (dilution) stage, sufficiently high intensity ultrasound can overcome the intermolecular adhesion and generate a large number of near vacuum microbubbles in the liquid. Bubbles inhale more gas during expansion and release it during contraction, resulting in a rapid increase in volume. This process is called "directed" or "rectified" diffusion. Due to the uniform distribution of bubbles in the liquid and the large total surface area during gas-phase acoustic cavitation, the migration rate of dissolved gases throughout the affected liquid volume is fast and uniform. The result is the formation of a large number of oscillating bubbles, which contain gases previously dissolved in liquid media. When bubbles jump in the ultrasonic field, they accelerate and merge with each other, forming larger bubbles. This process proceeds quickly until the bubbles reach sufficient buoyancy, float on the liquid, and release the previously trapped gas into the environment.

 

 

Cavitation Phenomena:

 

Ultrasonic degassing is caused by cavitation phenomenon. Ultrasound passing through the liquid continuously compresses and expands it. High intensity ultrasound provides the energy required to disperse the liquid phase. When the maximum pressure is reached, liquid rupture occurs at points with weak cohesion. After this rupture, overpressure appeared at the point of rupture and some cavities were found to exist. In these voids, the gas dissolved in the liquid explodes in the form of bubbles after a short period of time.

 

 

 

Ultrasonic degassing experiment:

 

1. Removing dissolved gases (degassing)

Pour the liquid into a glass container ("initial sample") (without intentionally introducing bubbles, there are some suspended bubbles, but most of the gas to be removed contains dissolved volatiles (1.5%)). Then expose the sample to ultrasound for approximately 1 minute and 15 seconds ("ultrasound exposure"), during which the dissolved gas is extracted from the liquid in the form of large suspended bubbles. Afterwards, let it stand for about 5 minutes to allow the bubbles with extracted gas to surface and rupture ("bubble surface and rupture"), resulting in the "degassed sample" shown in the following figure. The cavitation intensity undergoes significant changes during the ultrasonic process, and sometimes this "intensity jump" is used as an automatic method to end the degassing process.

The reason for its occurrence is as follows: the ultrasonic generator operates in constant amplitude mode: once the ultrasonic amplitude is set, it always remains at the same level. The power provided by the generator is automatically adjusted based on principles similar to those used in car cruise control, increasing the engine power output to maintain a constant speed (in our example, amplitude) when going uphill. When volatile fractions are completely degassed from oil, their properties suddenly change: cavitation enters a vacuum bubble state instead of an inflated bubble state. For the same amplitude setting, this will result in higher power consumption, leading to a "jump" in cavitation intensity.

 

 

2. Remove suspended bubbles (degassing)

Firstly, use a handheld mixer to introduce bubbles into the liquid ("introducing bubbles"). Then expose the sample to ultrasound for approximately 1 minute and 15 seconds ("ultrasound exposure"), during which small suspended bubbles merge into larger bubbles with higher buoyancy. After this step, there is a standing period of approximately 5 minutes to allow the large bubbles to surface and rupture ("bubble surface and rupture"), resulting in the "degassed sample" shown in the following figure.

 

 

Advantage:

 

1. Compared with other processes, ultrasonic degassing does not require high temperature, high pressure, good safety, simple operation, and convenient maintenance.

2. Compared with conventional methods, ultrasonic equipment is simple, has low production costs, and significant comprehensive economic benefits.

3. It has broad spectrum and wide applicability, and the vast majority of liquids can be degassed using ultrasound.

4. Keep your liquid material effect consistent.

5. Eliminate dissolved gases and/or entrained bubbles that interfere with the intended use of the liquid.

6. Improve appearance while degassing, homogenizing, and extending the shelf life of the liquid.