# Innovative Ultrasonic Spray Methods for Indoor Disinfection
## 3 Methods
### Testing Methodology  
For measuring the droplet size distribution produced during ultrasonic spraying of a thin liquid layer, the following methodology was employed. The electronic generator (2) was activated, applying voltage to the piezoelectric elements of the sprayer (1). Then, the liquid was supplied using the peristaltic pump (3) at a minimum flow rate of 0.5 mL/s. The flow rate was gradually increased to the nominal values listed in Table 1. The liquid flow rate was monitored using the flow meter (5). Once the required flow rate was stabilized (over 30 s), droplet size characteristics were measured using the Malvern SprayTec analyzer. Measurements were taken at a frequency of 2 Hz and averaged over 60 readings (30 s of measurement time). All statistical processing and determination of the main droplet size distribution metrics were performed using the SprayTec software (version 3.20).  
For these measurements, the compressor (5), nozzle (7), vacuum aspirator (9), and sound pressure meter (10) were not used in the experimental setup.  
The droplet size measurement methodology for the combined cavitation sprayer was similar to the one described above, except that the air compressor (5) was used to create excess pressure in the liquid. Before starting measurements, the pump (3) filled the receiver (4) to 90% of its volume (3 L) with liquid. The air compressor (5) was then used to establish and maintain the required pressure in the receiver and the liquid. In this case, the liquid flow rate was controlled using the flow meter (6). The rest of the measurement procedure was identical to the one described for ultrasonic spraying of a thin liquid layer.  
Figure 12: Structural diagram of the experimental setup. 1—Tested sprayer; 2—Ultrasonic generator; 3—Peristaltic pump; 4—Receiver; 5—Air compressor; 6—Flow meter; 7—Nozzle; 8—Malvern SprayTec analyzer; 9—Vacuum aspirator; 10—Sound pressure level meter.  
When studying the characteristics of the multi-stage sprayer, large droplets were introduced into the input of its tubular emitter (at either end of the tubular emitter shown in Figure 9) using nozzle (7). The nozzle produced liquid droplets with a size of 1500-2000 \(\upmu\)m (initial droplet size) at a flow rate of 5-30 mL/s. Droplet size characteristics were measured at two points [22]:  
1. Approximately one-third of the distance from the upper end of the tubular emitter, after droplets passed through the first antinode of the standing wave inside the emitter. A vacuum aspirator was used to collect aerosol droplets at this stage, corresponding to the first stage of atomization.
2. 50 mm from the lower end of the tubular emitter, to determine the droplet size characteristics of the aerosol produced after the multi-stage atomization process.  
When investigating the multi-stage sprayer's characteristics, sound pressure levels were measured using an Ecofizika-110A sound-level meter with a VMK-401 microphone (Ecofizika-110A, OKTAVA-ElectronDesign LLC, Moscow, Russia). Measurements indicated that the sound pressure levels inside the tubular emitter ranged from 160 to 182 dB.  
The measurement procedure involved adjusting the output power of the ultrasonic generator (2) to establish an initial sound pressure level of 160 dB inside the tubular emitter, monitored using the sound pressure meter (9). The liquid flow rate was set and maintained using the pump (3) and the flow meter (6). Initially, the flow rate was set at 1 mL/s. Droplet size distribution measurements were then conducted with the SprayTec analyzer as described for ultrasonic spraying of a thin liquid layer. Afterward, the sound pressure level inside the tubular emitter was increased by 5 dB, and the procedures were repeated. Similar measurements were performed for different liquid flow rates.  
This methodology enabled tracking the reduction in droplet size at each stage of atomization and evaluating the resulting droplet size distribution [22].  
4 Discussion of the Results of the Development of Methods and Devices for Spraying Disinfect Liquids