3.2.2. Hand-Type Nozzle

Similarly to the cannon-type nozzle, the three studied droplet size variables in the hand-type nozzle also depend on the HP, LFR and AS (*p* < 0.001). This fact is consistent with the air speed decrease found in the hand-type nozzle (Figure 4). General droplet size interval for every tested position can be observed in Figure 5b. Droplet size was more heterogeneous in the XP compared to that observed in the cannon spout.

The D50 values measured for the hand-type nozzle (Figure 7a) were slightly higher than those obtained in the cannon spout. Thus, CP resulted in D50 below 150 μm, with the minimum mean value of 62 μm for the combination between minimum LFR and maximum AS. XP, on the other hand, resulted in D50 values above 125 μm, with a maximum value of 407 μm for the combination of minimum LFR and minimum AS. In this particular case, the atypical behavior already observed for the cannon was also registered in the hand-type spout, with a decrease in the droplet size with the increase in the LFR. There was also a considerable influence of the other two evaluated parameters (*p* < <sup>10</sup>−3) on D50. In the case of LFR, there was a positive effect on D50, whilst the opposite was found for AS, as expected from previous works [53]. The mean D50 increase that can be found between CP and AP was 42%. From AP to OP there was a mean increase of 39%. Last, OP to XP had a mean VMD increment of 75%.

**Figure 7.** (**a**) D50 (Volume Median Diameter, VMD), (**b**) D10 and (**c**) D90 values (μm) per liquid hose position (HP), liquid flow rate (LFR) and airflow speed (AS) for the hand-type nozzle. Bars show the mean ± Standard Error. CP, conventional insertion of liquid hose position; AP, alternative position; OP, out position; XP, extreme position.

The D10 values (Figure 7b) comprised a minimum value of 23 μm for the combination of CP, intermediate LFR and maximum AS, and 179 μm for the combination of XP, minimum LFR and

minimum AS. The CP presented D10 values all below 50 μm, while the XP presented values above 55 μm. The mean increase in this parameter from CP to AP was 49%, from AP to OP it was 3% and from OP to XP it was 135%.

The D90 values (Figure 7c) were all found below 280 μm in CP and above 370 μm in XP. The most extreme values were 112 μm (for CP/min LFR/max AS) and 735 μm (for XP/min LFR/min AS). The mean increase from CP to AP was 35%, from AP to OP it was 28% and from OP to XP it was 94%.

In general, it can be observed that the most extreme positions generated an atypical response of the LFR on the droplet size parameters. Nevertheless, the three LFR levels did not produce grea<sup>t</sup> di fferences in comparison with the AS ones. It could be stated that LFR had a lesser impact on droplet size in the outermost positions of the liquid hose.

#### *3.3. Cumulative Sprayed Volume Curves and Their Classification According to ASABE S572.1*

The cumulative sprayed volume curves, obtained with cannon (Figure 8) and hand-type (Figure 9) nozzles by testing all configurations (combination of HP, LFR and AS), compared with the American Society of Agricultural and Biological Engineers (ASABE) nozzles classifications (ASABE S572.1) [63], showed that an appropriate selection of pneumatic sprayer operational parameters, namely LFR and AS, led to a limited change in the spray quality generated, varying from very fine (VF) to fine (F) in the best cases. On the contrary, changing HP deeply a ffected the spray quality and reached the coarse (C) (Figure 8) and very coarse (VC) (Figure 9) spray quality when the liquid hose was tested in the extreme position (XP) combined with reduced AS, irrespective of LFR. Even if Balsari et al. [53] recognize the importance of a proper selection of LFR and AS parameters in order to vary the spray quality in conventional pneumatic sprayers, likewise it was clear that the spray quality extent change from VF to F was not enough to guarantee environmental safeguard, despite the increased droplet size dimension. For this reason, according to the preliminary tests performed by Miranda-Fuentes et al. [55], the HP change along the pneumatic spouts is proven as the driving factor for changing the spray quality. This strategy allows to achieve a range of di fferent spray qualities comparable to that reachable with hydraulic nozzles, which can be varied in type (conventional vs. air induction) and size [43]. Thus, at the time of application, in both pneumatic nozzle types the selection of HP allowed to vary the spray quality in a wide range without changing the other operational parameters selected for the application (LFR and AS). In detail, the cumulative sprayed volume curves derived from the tested configurations using the liquid hose in conventional position (CP) showed a droplet spectrum similar to the hydraulic nozzles Albuz ® ATR lilac used at 0.7 MPa (Figures 8 and 9) and selected as reference. Only the hand-type nozzle tested in CP position with AS of 59.7 and 64.6 m s<sup>−</sup><sup>1</sup> showed a coarser spray quality, namely fine (F), irrespective of LFR (Figure 9). On the contrary, none of the tested configurations with both cannon- and hand-type pneumatic nozzles in XP position achieved the extra coarse (XC) spray quality, likewise that generated by the air-induction Albuz ® TVI8001 nozzles (0.7 MPa pressure) used as reference nozzle for the coarse spray quality (Figures 8 and 9). In general, the liquid hose position in AP and OP allowed intermediate spray quality, varying from F to M according to the LFR and AS selected. Even when the hand-type nozzle generated averagely larger droplets than the cannon-type did, the spray quality produced by both of them, for the same tested configuration, was very similar (Figures 8 and 9). In practice, no substantial di fference in prospective coverage of the leaves and fruits could be noticed between the two nozzle types. In any case, the possibility to vary in a wide range the droplet size by simply adjusting the liquid hose position gives, for the first time, the opportunity to both farmers and technicians to match the environmental requirements, balancing at the same time the treatment specifications for every spray application while using pneumatic spraying in vineyards. Recently, Grella et al. [58] demonstrated through field trials that the variation in the spray quality over the range investigated (from CP to XP) did not a ffect the canopy coverage, while coarser sprays (liquid hose in AP and XP) produced greater deposits on the target. Concurrently, the use of cannon spout in XP position significantly reduced the o ff-field ground losses in the downwind area.

**Figure 8.** Cumulate sprayed volume (%) curves as a function of droplet size (μm) per liquid flow rate (LFR), airflow speed (AS) and liquid hose position (HP) for the cannon-type nozzle. In each graph the hydraulic reference nozzles hollow cone conventional ATR lilac and air-induction TVI 8001 (Albuz®) are displayed, both operated at 0.7 MPa pressure. CP, conventional insertion of liquid hose position; AP, alternative position; OP, out position; XP, extreme position. VF, very fine; F, fine; M, medium; C, coarse; VC, very coarse; XC, extremely coarse; UC, ultra-coarse/unclassified; (ASABE S572.1).

**Figure 9.** Cumulate sprayed volume (%) curves as a function of droplet size (μm) per liquid flow rate (LFR), airflow speed (AS) and liquid hose position (HP) for the hand-type nozzle. In each graph the hydraulic reference nozzles hollow cone conventional ATR lilac and air-induction TVI 8001 (Albuz®) are displayed, both operated at 0.7 MPa pressure. CP, conventional insertion of liquid hose position; AP, alternative position; OP, out position; XP, extreme position. VF, very fine; F, fine; M, medium; C, coarse; VC, very coarse; XC, extremely coarse; UC, ultra-coarse/unclassified; (ASABE S572.1).

## *3.4. Droplet Homogeneity*

Significant di fferences (*p* < 0.001) were found in both nozzles for every single variable and their interactions. In general, it could be stated that the distance increase to the CP generates an increase in the droplet heterogeneity (Figure 10). This result is in line with the results obtained in previous works for the CP and the AP [55]. RSF values were slightly lower in the hand spout than in the cannon one (1.63 vs 1.78), especially in the surroundings of the CP.

In the cannon spout, the hose position change, although statistically significant, did not generate major di fferences in the mean RSF values (Figure 10a). Thus, values for every single position were near 2.00. The observed trend was a reduction in the droplet population homogeneity with the distance increase from the CP. The increase in AS also increased the RSF in general, especially in the case of the lower LFR in the CP (Figure 10a).

There was a much higher influence of the hose insertion position in the case of the hand spout (Figure 10b). In this case all values were around 2.00, but with important di fferences among the tested hose positions. There was a significant particularity in the hand spout case: values presented a higher RSF in the OP than in the XP, while the opposite would have been the most predictable scenario (Figure 10b). It should be pointed out that in this nozzle both LFR and AS had a higher impact on the RSF than they had in the cannon spout.

**Figure 10.** Relative SPAN Factor (RSF) per liquid hose position (HP), liquid flow rate (LFR) and airflow speed (AS) for both the (**a**) cannon-type and (**b**) hand-type nozzles. Bars show the mean ±Standard Error. CP, conventional insertion of liquid hose position; AP, alternative position; OP, out position; XP, extreme position.

The comparison between both nozzles regarding the droplet homogeneity follows a trend similar to that observed in previous works [53]. In those, a positive influence of both LFR and AS was observed on the RSF in both nozzles. Similarly to the present findings, the cannon spout had a higher RSF than the hand-type one did. A marked increase in the droplet heterogeneity was also observed in the maximum AS and minimum LFR combination (Figure 10a). This could be explained by the fact that with a very low LFR the amount of sprayed liquid might be insu fficient for the high air current to produce an optimal water division into homogeneous droplets, thus increasing the amount of very fine ones, altering their normal distribution and increasing the droplets heterogeneity by a ffecting the kurtosis.
