# The Development and Analysis of a Multistage Spraying Method for Liquids in an Ultrasonic Field
## 5 Conclusions  
The development of new liquid atomization devices and methods that can produce a fine spray at high throughput is of significant interest for various technological applications. For example, high dispersion, together with high productivity in aerosol creation, are required in the technological processes of aerosol drying, aerosol coating, surface treatment, and the spraying of drugs. In this study, a method of multistage spraying was proposed, consisting of the generation of a large number of particles of large initial diameter (to ensure high productivity) and their subsequent destruction in a periodic ultrasonic field (to ensure small droplet sizes at high productivity). For the practical implementation of the method, an ultrasonic emitter was developed in the form of a cylinder with a stepped-variable cross-section for the formation of bending-diametrical vibrations. The shape of this emitter in the form of a hollow cylinder was chosen to ensure the self-focusing of ultrasonic vibrations in the internal cavity on the cylinder axis. The developed emitter provides the generation of a periodic ultrasonic field with a frequency of 22.2 kHz and sound pressure level of up to 182 dB. The configuration of the ultrasonic field inside the emitter enables three-stage spraying. It was shown that the disperse characteristics of the formed droplets mainly depend on the sound pressure level at which the droplets break down. So, the increase in the sound pressure level from 160 dB to 182 dB changes the average diameter of the formed droplets in the range of 34-170 \(\upmu\)m, while the spraying productivity is not changed. The physical properties of liquids have a much smaller effect on the diameter of the formed droplets. In this way, an increase in viscosity from 1 mPa-s (water) to 3.7 mPa-s (40% aqueous solution of glycerin) indicates a weak increase in the median diameter of the formed droplets (no more than 2 \(\upmu\)m). A further increase in the viscosity of the liquid results in an increase in the median diameter of the resulting droplets, up to 57 \(\upmu\)m. In turn, the result of decreasing the surface tension of the liquid from 72.8 mN/m to 25.6 mN/m is a further decrease in the droplet size by 8 \(\upmu\)m.  
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