# The Development and Analysis of a Multistage Spraying Method for Liquids in an Ultrasonic Field
## 3 Ultrasonic Emitter
1—emitting element in the form of a bending and oscillating tube; 2—concentrator of the piezoelectric transducer (emitting pad); 3—piezoceramic elements; 4—reflective pad; 5—housing; 6—flange; 7—enforcement for the threaded hole; 8—amplitude adjustment area of the emitter ends; L—emitter length; D1—inner diameter; D2—outer diameter. The acoustic power of the developed emitter was determined. It was determined as the difference between the total electrical power consumed by the emitter and the emitter's own loss power. The measurement methodology was as follows. The total electrical power consumed by the ultrasonic emitter from the generator was determined as the sum of the acoustic power emitted into the gaseous environment and the power of its own losses in the emitter. The acoustic power emitted into a gaseous medium is proportional to the density of the gas multiplied by the speed of sound in the gas. Accordingly, if the gas density is reduced to values close to zero (by pumping gas out of the volume in which the emitter is installed), then the acoustic power will also become zero. In this case, the electrical power consumed from the generator will decrease and become equal to the power of its own losses in the emitter material. Thus, the acoustic power of the emitter can be defined as the difference between the electrical power consumed by the emitter from the generator at normal pressure and the electrical power consumed from the generator when the emitter is operating in a vacuum. The loss of power was estimated by measuring the power consumed by the emitter when operating without a load. For this purpose, the emitter was placed in a vacuum chamber [27]. The air was evacuated from the vacuum chamber to a residual pressure not exceeding 1000 Pa. The electric power consumed by the emitter was measured using the MT-1010 measuring instrument (Motech Industries Inc., Taiwan). The performed calculations and measurements enabled an estimation of the main technical parameters of the developed tubular emitter (Table 1). A test bench was developed in order to experimentally assess the feasibility and efficiency of the proposed method for the multistage spraying of liquids. The design diagram of the test bench and its image are shown in Figure 4. The test bench allows carrying out high-speed video recording of the droplet-breaking process and estimating the dispersion characteristics of the generated aerosol depending on the sound pressure level and liquid properties. The test bench consists of an ultrasonic tubular emitter (3) with a piezoelectric transducer powered by an electronic ultrasonic frequency generator (4), a dispenser (1) with \begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Value** \\ \hline Dimensions of the tubular emitter, mm & D2 = 92 \\  & D1 = 52 \\  & L = 96 \\ Vibration frequency, kHz & 22.2 \\ Electric power consumption, W & 50 \\ Amplitude (sweep) of the surface vibrations, max–min & 51–40 \\ Acoustic power, W & 35 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Lists the main parameters of the developed tubular emitter. Figure 3: Developed ultrasonic tubular emitter: (**a**) distribution sound pressure inside the emitter; (**b**) ultrasonic tubular emitter image. mounted nozzle (2), and an optical aerosol analyzer (6) from Malvern SprayTec. The operation principle of the analyzer is based on laser diffraction. The Spraytec analyzer enables the measurement of particle dispersivity with a frequency up to 10 kHz in the range from 0.1 to 2000 \(\upmu\)m. During the experiments, the sprayed liquid was fed by a peristaltic pump (1) into the nozzle (2) installed at the end of the tubular emitter. The nozzle generated liquid droplets of 1500...2000 \(\upmu\)m in size (initial droplet size) with productivity up to 20 mL/s. The dispersion characteristics were measured at two points shown in Figure 4:  
1. At a distance of approximately 1/3 from the upper end of the tubular emitter, after the droplets passed the first standing wave vibration's anti-node inside the emitter.