Effect of Physical Properties of an Emulsion Pesticide on the Atomisation Process and the Spatial Distribution of Droplet Size
Round 1
Reviewer 1 Report
The manuscript focuses on the evaluation of the effects of emulsion pesticide on drop size distribution of a spray produced by a nozzle used for pesticide applications. In particular, the Authors studied the process of generating droplets produced by a flat jet nozzle with an opening angle of 110°, at three operating pressure values and using water with and without pesticide emulsion at three different concentrations. In this way, they tried to explain the reasons for changing in the variability of the drop size distribution and how the presence of emulsion pesticide can help reduce drift without excessively increasing the maximum size of the droplets, which can cause run-off. To this aim, the Authors also evaluated variations of some volumetric diameters such as Dv50, V100 and V400 of the drop size distributions.
Considering that the aspects studied should have both economics and environmental effects (reduction of the amount pesticide used, drift and loss on the ground due to run-off) the thematic is actual and relevant.
In my opinion, the manuscript is well organized and reports the different aspects analyzed, but some results should be better explained (please, see the specific comments) and the text needs careful revision.
For the reasons given above, the manuscript requires a major revision.
Specific comments
Row 159: The Authors introduce the “surface energy of the liquid flow” that, I think, should be the surface tension. In my opinion, it is better to directly use the term surface tension, so as to be congruent with the definition of the symbol of the equation 1.
Rows 160—164: The Authors refer that they calculated the Weber number at varying of the pressure in the range from 0.1 to 0.5 MPa (9 pressure values, so I think with a step of 0.05 MPa) by spraying water without and with 0.1 % of butachlor, with the aim of “to compare the effects of physicochemical properties of spray and pressure on the two fragmentation mechanisms”. In my opinion, the Authors should state explicitly declare what fragmentation mechanisms they refer to. Furthermore, all section 3.1, excluding figure 3 and its comments, should be anticipated in the section material and methods.
Rows 167—168: In my opinion, surface tension is not a coefficient; moreover, what is the characteristic length?
Rows 169—170: The Authors introduce the spray angle which, as a first hypothesis, I consider to be the opening angle of the spray in the xy plane. Reading the following paragraphs of the results, they correlate the Weber number only with the diffusion angle (the opening angle of the spray in the yz plane). The Authors should use only one definition for the same parameters so as not to introduce doubts to the reader. For the sake of clarity, what they mean by spray angle should be defined here. Finally, I must point out that the angle is not a dimensionless quantity; in the International System of Units it is measured in radiant.
Row 208: Figure 6 should be moved after it has been recalled in the text. I do not well understand how figure 6 (a) highlights. What are the fragmentation mechanisms that cause the variations of the liquid sheet breakup length which, however, are fairly constant especially with the emulsion? Is the time in the axis of the ascisse the monitoring time or the time necessary to the occurrence of the liquid sheet breakup? In addition, in figure 6 (b) why are the data related to the pressures of 0.55 and 0.6 MPa, if the Authors have stated that they have carried out the study in the range from 0.1 to 0.5 MPa? At last, what is the concentration of the emulsion? I think 0.1 %, but where are the data for concentrations of 0.02 and 0.5 %?
Rows 227—241: The difference of liquid sheet breakup length, especially with the emulsion, are so small that, in my opinion, is difficult to highlight trends or fluctuations. The Authors should perform an ANOVA to evidence if there are statistically significant differences between the data.
Rows 273—274: The Authors claim that “resulting in smaller droplet size, which may have a positive effect on reducing the drift during spray” but, in my opinion, smaller droplets have a higher drift risk. Please, check the sentence.
Figure 8 (a): Please, see the observation on figure 6 regarding the emulsion concentration.
Figure 8 (b): It shows again two sets of data: water and emulsion, but this is not declared by different symbols and a legend.
Rows 289—293: In my opinion, the Authors should report the experimental data that support the sentences written in these rows.
Figure 9: Again, the graphs are related to water and a single emulsion concentration (probably to 0.1 %, but this is not explained). Looking at figure 9 (b) it is anomalous that, considering the last abscissa value of each data set and the distance of 50 mm from the nozzle, the resulting spray angles range about from 125° to 165°, higher than the reference spray angle (110°) of the nozzle used in the test. How do the Authors explain this aspect?
Author Response
Dear reviewer:
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The research carried out by the authors is relevant from the point of view of analysis and modeling of hydrodynamic systems, specifically spraying mechanisms. On the other hand, the manuscript does not characterize or properly contextualize, on the agricultural perspective, i.e., the experiments do not characterize the agricultural spray process, as well as some of the few comments, made by the authors, on agricultural spraying are placed wrongly, reaching conceptual contraditions within the same text. In this sense, some of the relevant comments are placed following (other comments and suggestions are marked in the attached PDF):
11) In the introduction there is not enough information about research works that study the effect of physical properties of an emulsion pesticide on the atomization process and the relationship with the distribution of drops. This fact, indicates a poor state of art at work submitted by the authors.
2) The manuscript does not explain in detail the experimental setup used. In this sense, the technical and methodological specifications used in the experimental data collection must be placed and formalized in the text. The lack of technical information largely reduces the level of the manuscript submitted by the authors. Therefore, in order to obtain repetition, the technical configuration of the experimentation system must be detailed. Thus, technical characteristics of each of the elements used, i.e., structure dimensions, pressure control system, data system acquisition, etc., must be placed in detail.
3) The study of the Emulsion effect of pesticide liquids on the creation of drops and their respective distribution (spectrum of drops) is of great importance. Therefore, studies in this field of research help to understand the improvements that the use of this type of methodologies can have on the application. From the practical application point of view, spray bars are used in which several spray nozzles (normally spaced between 30-40 [cm] of each other). In this sense, the experiments carried out by the authors of the manuscript do not characterize the effect of the overlap that the jets that leave the spray nozzles have. This fact is as much or more important than the height at which the spray nozzle is placed in the application. Thus, using only an application nozzle as a study basis does not really allow you to understand or study the effect on real agricultural pesticide spray applications.
4) In lines (153-154) the authors place the following statement: “The size of droplets is not sensitive to liquid viscosity.” This is a strong statement, was it experimentally confirmed? Or, was this statement based on a bibliographic reference?
5) The authors make the following statement (lines 272-274): "The stronger the disturbance flapping, the thinner the liquid sheet would be stretched, resulting in smaller droplet size, which may have a positive effect on reducing the drift during spray". This sentence is wrong. In hydrodynamic terms, smaller drops have greater drift potential in relation to thicker drops (larger diameters). Small drops generate more uniformity in the application and serve for superficial treatments at the top (in crop leaves). On the other hand, larger drops have more penetration for treatments at the bottom of the plants.
6) In the conclusions (lines 445-446) the authors make the following statement: "In the process of pesticide spraying, the pesticide loss is large due to the unevenness and drift of droplets [34]". In the conclusions, the use of bibliographic citations must be avoided. The conclusions must be original and based on the results found.
Note: Some other details of correction and suggestions on the formalism, writing and analysis are placed in the revision made in the attached pdf.
Finally, the scientific manuscript submitted by the authors is important and has a lot of relevance for scientific journals that deal with spray mechanisms, but for scientific journals on agricultural processes (as is the case of Agriculture Journal) the manuscript has a very poor agricultural contextualization. This fact makes it not a relevant investigation and does not have a direct impact on the methodologies or technologies for the application of pesticides.
Comments for author File: 
Comments.pdf
Author Response
Dear reviewer:
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
In my opinion the article on Effect of Physical Properties of an Emulsion Pesticide on the Atomisation Process and the Spatial Distribution of Droplet Size (1732649) is well prepared.
In the body of the paper, the purpose of the paper is not precisely detailed, but it follows from the planned research experiment. This is described in the material and methods chapter. The experiment is well planned. Good measuring apparatus was used. With the help of high-speed cameras, it was seen how the liquid spray is produced with the use of flat jet nozzles. Today, flat-fan nozzles are the most commonly used nozzle in agricultural spraying technology. UAVs (Unmanned Aerial Vehicles), which are equipped with spraying systems, are already in use. When using UAVs for spraying, the quality of the spray and the reduction of droplet drift are important. This paper describes droplet formation using water and water with adjuvant. As a rule, adjuvants are supposed to change the properties of the liquid so that the resulting droplets have better contact with the plant and stay on it longer. The addition of an adjuvant to a UAV spray is important and even necessary in order to obtain a proper droplet spectrum. This paper describes the results of a study on how droplets are formed from a film of liquid flowing out of a nozzle. It was found that not only the pressure of the liquid but also its parameters are important for the resulting droplet spectrum. It was found what should be the optimum concentration of adjuvant in water, which significantly affects the formation of drops. The article can be useful for designers and technicians who design spray nozzles. It can also be useful for practice.
It would be good if y in the article there was a reference for what type of water the adjuvant was used. What is the water hardness and surface tension, and what is the elemental content. Waters are different and may react differently to an adjuvant.
I think you could look into other threads that affect the way liquid is sprayed through slit nozzles.
I propose to change the keywords spray atomization to spray nozzle , line 24.
But this article, for those reading it, may be an inspiration to develop new methods of measurement and to look for solutions that affect the way droplets are rendered for a split spray.
Author Response
Dear reviewer:
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The Authors have modified their manuscript according to some indication provided in the previous review but, in my opinion, still need improvements. In particular, the Authors should ensure that the materials and method section is consistent with the reported results. In detail, the Authors have studied the fragmentation mechanism to vary the pressure in the range from 0.1 to 0.5 MPa with steps of 0.05 MPa (9 values) (this is indicated only in the results section 3.1) with two solution (water and of water-butachlor emulsion at the concentration of 0.1 %), while in materials and methods they indicated that three concentrations of butachlor (0.02, 0.1 and 0.5 %) were considered. Really, they reported the effects of all three concentration only on the percentage volumes V100 and V400, and evidenced some differences only in the paragraphs 3.3.2. This is the reason why I have asked to anticipate all section 3.1, excluding figure 3 and its comments, in the material and methods section. In fact, from the line 157 to the line 175 there are no results but the explication why they have chosed to consider two dimensionless parameters: the diffusion angle and the Weber number with its definition.
Therefore, I think the manuscript still needs a major revision.
Specific comments
Row 80: The sentence “Three concentrations of butachlor were considered, which is 0.02%, 0.1% and 0.5%.” should be revised integrated with what reported in the rows 167—168. I also suggest to move these indications after the description of the method and the instruments used to calculate the surface tension that I have really appreciated.
Row 91: Please, complete the model nozzle used. On the market there is a series of ST-110 nozzle: from ST 110-01 to ST 110-08.
Row 325: I think that “0.3 MPa” should be substituted with “50 mm from the nozzle outlet”.
Row 336, 338, 345: In my opinion, “target” should be substituted with “nozzle”. Instead, “target” is appropriate in row 348.
Figure 8b: I do not agree with the comments of the Authors: “Non-dimensionalized data could be declared by the same symbol”. Each graph should be immediately interpretable by the reader. The Authors, in row 286, refer to the series related to the emulsion, but to identify it, you need to compare Figure 8b Figure 8a. In the end, in my opinion, two different symbols must be used.
Figure 9: I agree with the Authors that they did not measure the spray angle, but they moved along the x-axis until droplets were detected, so it is likely that there are differences; in my opinion, these are very high: 165° again 110°.
Generic comments
Figures: The concentration of the butachlor in the emulsion should be indicated in each legend or caption if the legend is not present. Furthermore, a blank space should be inserted between the variable name and the round bracket; for example:
· Pressure (MPa) and not Pressure(MPa)
· We (Weber number) and not We(Weber number)
· T (ms) and not T(ms)
Measurement units: a blank space should be inserted between the value and the measurement unit; for example:
· 50 mm and not 50mm (see row 350)
· 100 µm and not 100µm (see row 357)
Please, check along all the text.
Author Response
Dear reviewer:
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 2 Report
I am satisfied with the answers placed by the authors for each of my questions and concerns. Also, the authors accepted and corrected most of my suggestions of improvement. I think the manuscript improved considerably and increased the formal level and impact on the area of agriculture.
Author Response
Dear reviewer:
We would like to thank you for your careful reading, helpful comments, and constructive suggestions, which has significantly improved the presentation of our manuscript.
Thank you again for your approval of the article!
