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The principle of ultrasonic atomization

2020-09-24 11:42:52

 

Relevant research believes that ultrasonic atomization is the process of using ultrasonic energy to make liquid form fine droplets in the gas phase. That is, ultrasonic waves are generated on the vibrating liquid surface, and the vibration peak formed by the amplitude separates and breaks the droplets from the surface. As the ultrasonic frequency increases, the atomized droplets become finer and finer. Generally, fine droplets can be obtained under the action of the vibration frequency of the ultrasonic wave. In addition, the ultrasonic frequency field can also eliminate or thin the temperature boundary layer near the heat transfer surface, thereby promoting heat transfer.

 

Ultrasonic atomizers are divided into two categories: hydrodynamic type and electro-acoustic transducer type. Hydrodynamic ultrasonic atomization uses high-speed gas or liquid to excite a resonant cavity to generate ultrasound. The frequency is mainly determined by the geometric size of the resonant cavity. The size of the droplet is related to the flow rate, air pressure and nozzle structure. Ultrasonic gas atomization technology uses hydrodynamic ultrasonic atomizers. In addition, ultrasonic atomization of liquid media such as water, organic liquids, and molten metals often uses this form.

 

The electroacoustic transducer type ultrasonic atomization uses a transducer to convert high-frequency electromagnetic oscillations into mechanical oscillations of liquids, which break the liquids into mist. There are two main forms: one is that the piezoelectric transducer radiates strong ultrasound in the liquid, radiates into the liquid through a thin sound-permeable membrane, and produces fountain-like atomization on the liquid surface, which is the principle of a typical ultrasonic humidifier; The other is that the liquid flows to the surface of the ultrasonic concentrator and forms a thin liquid layer. The thin liquid layer excites surface tension waves under the action of ultrasonic vibration. When the amplitude of the vibrating surface reaches a certain value, the droplets fly from the wave crest. Out and form atomization.

 

Atomizing nozzle is a device that enables the atomizing medium to obtain high energy and high speed in the atomizing device. It is also a key component that plays an important role in the level of atomization efficiency and the stability of the atomization process. Its function is to control the flow and flow pattern of the atomizing medium in order to effectively break the liquid metal and produce powder with specific properties. The atomizing nozzle is actually a transducer, which converts the kinetic energy of the high-pressure gas into the surface energy of the metal. As a transducer, its energy conversion efficiency is very important.



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