Introduction to the principle of ultrasonic atomization
Install the piezoelectric ceramic sheet (commonly known as ultrasonic atomizing sheet) at the bottom of a water container, and a drive control circuit generates a driving voltage consistent with the resonant frequency of the atomizing sheet and applies it to the atomizing sheet, and the atomizing sheet will generate Oscillation energy. The oscillating energy propagates in the water along the direction perpendicular to the surface of the atomizing sheet. In the case of a suitable water depth, the water surface on the energy propagation axis concentrates a water column, and a large number of tiny tension waves are concentrated at the front end of the water column, which makes the water surface rise. The surface tension of the water is greatly reduced, and the water surface is split into many tiny areas by the wavelength of the surface tension wave. principle.
Ultrasonic atomization is the process of using ultrasonic energy to form fine droplets of liquid.
There are two ways to atomize liquid by ultrasonic:
1. The thin liquid layer on the vibrating surface excites a capillary-gravity wave under ultrasonic vibration.
2. The atomization method is that the ultrasonic fountain forms fog.
There are two theoretical explanations for the principle. They are the micro shock wave theory and the surface tension wave theory, respectively.
On the one hand, the micro-shock theory explains that the cavitation effect produced by ultrasonic waves in the liquid medium leads to the generation of micro-shock waves and thus the phenomenon of atomization. This theory believes that the cavitation effect is the direct cause of the atomization of the liquid. When the cavitation bubble collapses, in addition to generating heat and light radiation, the rest is radiated in the form of micro-shock waves. Atomization When the micro shock wave reaches a certain intensity, it causes the atomization of the liquid.
On the other hand, the surface tension theory believes that the generation of droplets is due to the instability of the liquid surface wave, which causes the liquid to atomize. Under the action of the force perpendicular to the surface tension wave, once the amplitude of the vibrating surface reaches a certain value, the droplet will fly out from the wave crest to form atomization. This theory holds that a surface tension wave produces droplets at its crest, whose droplet size is proportional to wavelength. The model of the surface tension wave and the atomization model of the surface tension wave.
Fountain atomization, which is a common form, uses piezoelectric wafers as transducers to generate megahertz-level ultrasonic waves. Usually the formation mechanism of fountain atomization is as follows. When the ultrasonic frequency of the ultrasonic transducer is megahertz, the directivity of the ultrasonic wave and its cavitation field is very good, so the solution in contact with it will be sprayed to form an "ultrasonic fountain" .
A large number of aerosols are produced at the same time as the ultrasonic fountain is produced. Among them, the "ultrasonic fountain" can be regarded as an upwardly jetted ultrasonic cavitation field, which possesses a unidirectional radiation force and a symmetrical whirling sound flow. In this cavitation field, the distribution of cavitation bubbles is very different. When water and other liquids are cavitated, due to the effect of acoustic radiation pressure, due to the density of cavitation bubbles, due to the physical effect of ultrasonic radiation force and clustered jet, the concentrated thermal effect and mechanical effect of a large number of cavitation bubbles are more prominent at the front of the fountain. , the sound energy density is also greatly improved along the jet direction due to the ultrasonic free jet and bunch jet.
In the ultrasonic fountain, the high-temperature acoustic rush and high-pressure shock wave when a large number of cavitation bubbles collapse and burst are the main mechanisms of the ultrasonic fountain. And other mechanical stirring effects, thermal effects, etc. also exist at the same time. Ultrasonic humidifiers designed using this principle are often used as indoor humidification devices. It can humidify computer rooms and wool spinning workshops to remove static electricity from equipment; add drugs for indoor sterilization and disinfection, perform facial beauty, and shape bonsai.
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