*2.4. Data Analysis*

The data were recorded by Malvern Spraytech ® software, while a special macro was developed in R-Studio [61] to automatically import and compile the data of every replication with their work parameter combination labels. Data analysis was performed in IBM SPSS Statistics v25 [62]. Normality and homoscedasticity of data were checked by using Shapiro–Wilk and Levene tests (<sup>α</sup>=0.05 in both cases). Graphs were done with the SPSS and Excel graph editor.

A three-way ANOVA test (<sup>α</sup>=0.05) was run to test the influence of the three factors (HP, LFR and AS) on every single dependent parameter (D50, D10, D90, RSF and V100). A FREGW (Ryan-Einot-Gabriel-Welsh F) test (<sup>α</sup>=0.05) was then applied to set the homogeneous groups. Correlations were developed between D50 and V100 for both pneumatic nozzles tested.

The cumulative sprayed volume curves, obtained by each tested configuration together with the reference hydraulic nozzles were compared with American Society of Agricultural and Biological Engineers (ASABE) nozzle classifications (ASABE S572.1) [63].

#### **3. Results and Discussion**

#### *3.1. Airflow Speed Drop Along the Spouts*

The airflow speeds measured along the longitudinal axle of cannon and hand spouts are graphed separately in Figure 4. Specifically, Figure 4a shows an important decrease in the air speed from the inner to the outermost position for the cannon-type nozzle (about 55% in every case). Nevertheless, this decrease was not constant along the axle, registering a slight slope between 5 and 10 cm from the inner position and very important slopes from 16 cm on (Figure 4a). Thus, the speed decreased at a variable rate ranging from 0 to 3.67 m s<sup>−</sup><sup>1</sup> cm<sup>−</sup>1. The effect of the nozzle border on the speed decrease was noticeable: the air speed decrease was less extreme near of the spout border, becoming more important in the 12 cm after the first 6 cm interval. This effect could be due to a border effect of air enclosure before spreading out of the main current direction in the following sections. Concurrently, Figure 4b shows the response of the air speed in the hand-type nozzle. The two first sections, between the OP and the AP, kept the air speed relatively constant, with less than 10% decrease in total in the most extreme case (677 rev min−<sup>1</sup> of the test bench, Figure 4b). After the air spout border, there was an abrupt decrease in the air speed, with a maximum mean value of 7.56 m s<sup>−</sup><sup>1</sup> cm<sup>−</sup><sup>1</sup> in the case of the maximum test bench fan rotary speed.

**Figure 4.** Airflow speed (m s<sup>−</sup>1) measured along the longitudinal axle of the spout at different distances (cm) from the conventional position of liquid hose (CP) at four test bench fan rotary speeds: (**a**) cannon-type and (**b**) hand-type pneumatic nozzles. Error bars show the ± Standard Error of the Mean.

#### *3.2. Droplets Size Spectra Measured*

The VMDs, or D50 values, distribution per liquid hose positions are shown separately by nozzle type in Figure 5. In general, the cannon (Figure 5a) generated finer droplets than the hand-type nozzle did (Figure 5b), with median values in their conventional insertion position of the liquid hose (CP) of 76 vs 95 μm, respectively. This fact is consistent with the observations made in previous droplet size characterization tests [53]. Nonetheless, there was a higher capacity to proportionally increase D50 values in the cannon (265% vs 223% total increase from CP to XP, Figure 5), which makes it possible to produce relatively similar drops in the XP in both the cannon- and hand-type nozzles (270 vs 307 μm, Figure 5). When looking at the distribution of the D50 droplets in the different tested positions, values in the cannon spout were more homogeneously distributed than those in the hand spout. Thus, the first nozzle generated a D50 value of 74 μm at the reference position (CP), whereas values were 112, 205 and 270 μm at AP, OP and XP positions, respectively. The last three values corresponded to 51%, 177% and 265% droplet diameter increase when compared to the reference position (CP). For the hand-shaped nozzle, a 95 μm droplet diameter was recorded at CP. Diameters at AP (145 μm), OP (160 μm) and XP (307 μm) were 53%, 68% and 223% larger, respectively, than those recorded at CP. As it can be seen (Figure 5), values were more heterogeneous in the hand-type nozzle (b) when compared to the cannon ones (a). The D50 variability (shown by the interquartile rate in Figure 5) in both nozzles increased with increasing distances from CP. This is also consistent with previous works characterizing pneumatic sprayer droplet size, as the droplet size indicators (D50 among them) can be predicted with linear models, which are affected by the liquid flow rate and air speed [53]. When comparing these global results with the air speed decrease rate (Figure 5), data were consistent in the cannon-type nozzle. Air speed decrease did not present extreme values along any of the measured sections, so a progressive droplet size increase was expected. On the other hand, the hand-type nozzle presented more extreme air speed decrease values, so the higher heterogeneity of data would be explained.

**Figure 5.** Volume Median Diameter (VMD) (μm) per liquid hose position (HP): (**a**) cannon-type and (**b**) hand-type spouts. CP, conventional insertion of liquid hose position; AP, alternative position; OP, out position; XP, extreme position.
