Ultrasonic equipment can effectively degassing and defoaming liquid. In this case, ultrasound removes small suspended bubbles from the liquid and reduces the dissolved gas level below the natural equilibrium level.
Degassing and defoaming of liquids have many uses, such as:
Particle size measurement before sample preparation to avoid measurement error.
Before pumping, oil and lubricating oil are degassed to reduce pump wear caused by cavitation.
Degassing liquid food (if juice, soy sauce or wine) to reduce microbial growth and extend shelf life.
When the liquid is treated by ultrasonic wave, the sound wave propagating from the radiation surface to the liquid medium will produce alternating cycles of high pressure (compression) and low pressure (rarefaction), and its rate depends on the frequency. During the low-pressure cycle, high-intensity ultrasound will produce small vacuum bubbles or voids in the liquid. A large number of small bubbles are evenly distributed in the liquid, resulting in more bubble surface area. The dissolved gas migrates to these vacuum (low pressure) bubbles through a large surface area and increases the bubble size.
Sound waves support the contact and coalescence of neighboring bubbles, thus accelerating the growth of bubbles. Sound waves will also help to separate bubbles from the surface of the container and force smaller bubbles below the surface of the liquid to rise and release the entrained gas into the environment.
Influencing factors of gas
The fluid contains a certain amount of dissolved gas. The concentration of gas depends on factors such as temperature, ambient pressure, liquid agitation, etc. At constant conditions, the gas concentration will be close to equilibrium. Ultrasonic degassing will change the condition as the liquid is exposed to low pressure bubbles and stirred. Therefore, ultrasonic will reduce the gas concentration in the liquid to the original equilibrium level.
When ultrasonic treatment stops and the initial conditions are reestablished, the gas concentration will again slowly approach the initial equilibrium level, and again, the gas concentration will be slowly approaching the initial equilibrium level again unless the liquid is not exposed to any gas, such as in a closed bottle. Because the re dissolution rate of gas in liquid is slow, low gas liquid can be used after ultrasonic treatment.
Ultrasonic degassing can significantly improve the quality of dispersions and emulsions.
Existing problems
Emulsions and dispersions usually contain surfactants to increase stability. Surfactants will inhibit the contact and coalescence of dispersed materials in the liquid phase. For this purpose, the surfactant will form a layer around each particle. Similarly, surfactant can also wrap bubbles suspended in liquid phase. This stable bubble can prove to be very robust. It consumes surfactants, reduces the quality of emulsions or dispersions, and produces unstable readings when measuring particle sizes.
Solution
In order to reduce the problem of bubble stability, the liquid can be degassed simply by ultrasonic treatment. Before adding a dispersed phase (such as oil or powder), the liquid is ultrasonically treated until the number of bubbles produced is reduced. When mixing other materials, avoid the generation of new bubbles or vortices during mixing, which will rapidly increase the gas content.