*3.2. Mechanical Tests*

Figures 8 and 9 show the capabilities of the system to control speed and position. In particular, Figure 8 reports the position profiles vs. time recorded during the tests, while Figure 9 shows the speed profiles vs. position, directly obtained from the optical encoder. The profiles are almost superimposable for all the tests: The presence of the small quantities of noise is mainly due to limitations of the Windows operating system to accurately measure time intervals less than 100 ms. No malfunctioning was observed during all the experimental activities. In addition, the graphs show the platform reaching

the reference speed (1.5 m/s) before approaching the first Petri dish, keeping it constant until going over the last one. The whole trajectory was completed in about 2.3 s.

**Figure 7.** Main components of the test bench: (**a**) the whole system with the digital single-lens reflex (DSLR) camera and the wood table; (**b**) the main tank with the electric motor pump and the pressure regulators; (**c**) the mobile platform with the nozzle holder and the sensor pressure; (**d**) the cabinet with the electric components.

**Figure 8.** Position profiles of the mobile platform during the tests.

**Figure 9.** Speed profiles of the mobile platform during the tests.

#### *3.3. Spraying Test Results*

Air temperature and relative humidity during the experiments were 26 ◦C and 43%, respectively. The number of droplets detected in each of the analyzed images ranged from about 1700 to about 38,300. Taking into account all the images, the total number of sampled drops ranged from about 37,800 (0.3 MPa) to about 286,500 (1.5 MPa), much higher than the ISO 5682-1 requirements (representative samples composed by at least 2000 droplets).

Table 1 reports flow rate data for the nozzle under test, and Table 2 summarizes all the measured spray drop parameters in function of working pressures; mean values were computed assuming each Petri dish as an independent sample.


**Table 1.** Measured and reference flow rate values for the nozzle under test.

**Table 2.** Spray drop parameters in function of working pressures.


As expected, all diameters were affected by pressure: An increase in pressure determined a decrease in diameters, meaning a higher degree of drop pulverization. The measurement system was then able to correctly detect the influence of pressure changes. According to the Albuz catalogue, the spray quality of the ATR80 orange hollow cone nozzles at 0.5 MPa and over is classified as "very fine", based upon volumetric median diameter (VMD) *Dv*0.5 values lower than 159 μm, measured with phase Doppler anemometry (PDA) systems. Therefore, results obtained with the present test bench qualitatively agree with Albuz's information.

In addition, this measuring system was quite reliable and accurate: In fact, the coefficients of variation (CV) of all diameters (except *Dv*0.1 at 0.3 MPa and NMD) ranged between 1.9% and 8.6%. In the excluded cases, CVs ranged between 8.5% and 15.0%. As a general result, variability was higher when diameters were lower.
