Ultrasonic spraying differs from traditional spraying, relying on pressure and high-speed motion to shear the fluid into small droplets. Ultrasonic spraying uses only ultrasonic vibration energy to atomize. Ultrasonic atomizing spray equipment is considered “green” technology due to its low energy consumption and high efficiency, making it ideal for critical fluid applications.
Ultrasonic atomizing spray systems, also known as ultrasonic atomizers or ultrasonic spray nozzles, generate high oscillations from ultrasonic vibrations, producing extremely fine droplets, also known as “dry mist”. During the ultrasonic spraying process, the droplet size and distribution can be precisely controlled. Tiny droplet particles can evaporate quickly, resulting in particles with a high specific surface area.
Table of Contents
- 1 Ultrasonic atomization spraying principle
- 2 Types of ultrasonic atomizing nozzles
- 3 Additional Features
- 4 Influencing factors of ultrasonic spraying
- 5 Liquid Compatibility
- 6 Advantages of ultrasonic atomization spraying
Ultrasonic atomization spraying principle
Ultrasonic atomization spraying uses the piezoelectric effect to convert electrical energy into high-frequency mechanical energy to atomize the liquid. Ultrasonic high-frequency oscillation is used to atomize the liquid into uniform micron-sized particles. Compared with traditional pressure nozzles, ultrasonic spraying can obtain a more uniform, thinner and more controllable film coating, and it is not easy to block the nozzles. Since the ultrasonic nozzle only needs a small air volume of kilopascal level, its spraying process almost does not produce a splash, so the coating utilisation rate of more than 90%.
Ultrasonic spraying is a successful technology, e.g. for high quality and a high-performance coating on substrates. By precise control of the various process parameters of ultrasonic spraying, overspray can be avoided, and accurate droplet distribution is achieved. The advantages of ultrasonic spraying are the precise control of droplet size, spray intensity and liquid flow rate.
Types of ultrasonic atomizing nozzles
Different frequency and airflow channel design can create different atomization particle size and spraying width to adapt to different area, thickness, finish and other coating requirements, in addition, the unique design of the shape structure can also be adapted to high temperature, narrow space and other special environmental applications.
Ultrasonic pre-dispersion system
Ultrasonic dispersion syringe enables the solution to be ultrasonically dispersed before atomized spraying, avoiding solids’ precipitation during the spraying process.
Liquid transfer pumps
Ultrasonic atomizing spray equipment can be used with various liquid delivery systems, such as syringe pumps, gear pumps, peristaltic pumps, pressure tanks, etc. Regardless of which method is used, any of these systems will work as long as the liquid is delivered at a steady flow rate within the nozzle’s operating range. However, pulsations should be avoided (syringe pumps are recommended); even momentary vibrations may cause the fluid to fall outside the operating scope. This is especially true for low-flow applications such as stent coating.
Influencing factors of ultrasonic spraying
The frequency of the ultrasonic spraying equipment affects the droplet size; the higher the frequency, the smaller the droplet size. The median droplet size at 20 kHz is 90 microns, and at 40 kHz, the droplet size is further reduced to an average of 45 microns.
Success or failure of atomization
Cavitation will occur if the ultrasonic energy is too high. Too much power will not form the desired film at the tip of the nozzle, causing the liquid flowing through the nozzle to atomize prematurely and “tear” into droplets of varying sizes. Only the amplitude produced at a specific power can have a more desirable atomization effect. For ultrasonic atomization spraying, the input power level is typically around 10 to 15 watts.
Atomization Flow Rate
The flow rate range of ultrasonic atomizing nozzles is generally extensive, unlike conventional air-driven nozzles that rely on the force of air to break up the liquid stream for atomization. Therefore, the amount of liquid atomized by the nozzle per unit time of the same solution is mainly controlled by the fluid delivery system used in combination with the atomizing nozzle.
Various coatings, chemicals, lubricants and particle suspensions can be easily atomized. However, factors such as viscosity, miscibility and solids content are worth considering. For optimal atomization, the thickness should be below 40 cps and solids concentration should be kept below 30%. Since the ultrasonic atomization spraying process depends on the liquid film’s movement, the more dense the liquid is, the more difficult the atomization will be. Liquids with long-chain polymer molecules inside are more cohesive and difficult to atomize, even in diluted form. In general, mixtures of single particles are more comfortable to atomize.
Ordinary pure liquids
- Pure single component liquids (water, alcohol, bromine, etc.)
- Pure solutions (brine, polymer solutions, etc.)
- Mixed liquids with insoluble solids (coal slurry, beaded polymer/water, silica/alcohol, suspension, etc.)
For pure liquids, the only thing that affects the atomization effect is the viscosity, usually around ten cp maximum.
Polymer molecular liquids
Pure solutions are similar to pure liquids in most cases, except when the dissolved liquid contains very long chains of polymer molecules. In this case, the polymer molecules’ length affects the atomization process, and those polymer molecules prevent the formation of such discrete droplets when the droplets are separated from the whole liquid and thus form atomization.
Mixtures with insoluble solids
In mixtures with insoluble solids, three factors affect the atomization capacity: particle size, solid concentration and the dynamic relationship between the solid particles and the carrier.
The concentration of the solid particles is important, with an upper limit of about 30%, and at high concentrations, the right conditions have to be in place for atomization. Finally, even if the particle size is appropriate, the feasibility of liquid atomization is influenced by other dynamic factors, such as the viscosity of the carrier and the ability of the solids to remain in suspension.
If the particle size is greater than 1/10 of the median droplet value, the mixture is generally effortless to atomize. The droplet size must be much larger for droplets containing one or more solid particles than solid particles. Otherwise, most of the droplets will likely not contain the solid components and form a separation.
Advantages of ultrasonic atomization spraying
- Easy to form spray patterns for precise coating applications
- Can coat any shape object with uniform micron-thick coatings
- The ultrasonic atomized coating reduces downtime in critical production processes.
- Ultrasonic atomized coating with ultra-low flow rates for intermittent or continuous operation
- Highly controllable spray volume for more reliable coating quality
- Low energy consumption, high atomization efficiency and less restriction on atomized liquids
- Reduces waste and air pollution caused by back spraying, saving costs
- No pressure, no noise, no wear of moving parts, no clogging
- The atomizing nozzle is made of titanium material, with strong height and corrosion resistance.