1) Principle of Ultrasonic Atomization.
Ultrasonic atomization adopts ultrasonic generator self-excited oscillation with the transducer, It radiates intense ultrasonic waves into the water. The ultrasonic wave passes through the water and semi-permeable membrane to treat the atomized salt solution in the atomizer cup, which makes The microbubbles that exist in the salt solution vibrate in the acoustic field. When the sound pressure reaches a certain value, the micro air bubble expands rapidly and then suddenly closed and shock waves occurs.A series of dynamic processes such as expansion, closure and oscillation are called acoustic cavitation.Under the effect of acoustic cavitation, the liquid is dispersed in the gas phase and formed a fine mist on the surface of the liquid. The fine mist, driven by the flowing gas, continuously flows from the atomizing cup to realize ultrasonic atomization.The completer process is only a physical reaction, not a chemical reaction.
2) Control of Salt Mist Settling Volume in Ultrasonic Atomization Method.
The ultrasonic atomization method is very easy to control the deposition rate of salt fog, and the factors affecting the precipitation rate of salt fog are: temperature, pressure, concentration of salt solution, diameter of salt mist particles, and the speed of atomization.The diameter of the salt spray particles has the following relation with the ultrasonic frequency:
Ultrasonic frequency;Salt solution density;The surface tension of the salt solution.
It can be seen that when other conditions are certain, the salt mist deposition rate can be adjusted by adjusting the diameter of the salt spray particles.The higher the ultrasonic frequency, the finer the salt mist and the lower the deposition rate of salt fog.The purpose of controlling the sedimentation rate of salt fog can be achieved by adjusting the ultrasonic frequency.
The speed of atomization is closely related to the power of the ultrasonic wave, and the precipitation rate of the salt mist is adjusted by adjusting the power of the ultrasonic generator.Thus, the settlement rate in unit time is controlled.It can adjust the output of the salt mist by adjusting the air volume of the inlet of the atomizing cup.When the intake volume is large, the microbubbles that exist in the liquid will increase, and it is easy to form more fine mist. Meanwhile, due to the increase of pressure difference, the velocity of salt fog will be accelerated, and the amount of fog in the experimental area will increase.
The ultrasonic generator atomized the salt solution in the atomizer cup and diffused through the plastic hose into the test area. As the diffusion concentration increased, the salt mist began to settle.The higher the concentration of salt fog in the test area, the faster the settlement.The final settlement rate reaches equilibrium and tends to be stable.The salt solution concentration, pH value and temperature of each point in the test area meet the requirement of salt spray standard.
The precipitation uniformity of salt spray in ultrasonic atomization method is obviously improved, compared with that of air pressure injection.Compared with the air pressure injection method, the salt spray particles produced by the ultrasonic atomization method are fine and uniform, and the diameter can be controlled between several microns and 20μm with good consistency .The salt spray particles produced by the air injection method are non-uniform-- the diameter can be up to several hundred micrometers, which can result in the uneven distribution of salt fog and the reduced effective test area.