Airborne-Spray-Drift Collection Efficiency of Nylon Screens: Measurement and CFD Analysis

Round 1

Reviewer 1 Report

The presented article analyses the collection efficiency of nylon screens by means of experimental tests and CFD simulations. I consider that the article is within the scope of the journal and has the originality and significance of content necessary to consider its publication after some minor corrections.

The introduction is well formulated, with a strong theoretical basis and the references are adequately selected with respect to the content. The materials and methods section is clearly written, and the organization of the section facilitates the reading of the article.

Suggestions for minor corrections 

1.- Regarding the experimental assays, I find the use of the TOC analyzer interesting. This assay improves both the originality and significance of the article by presenting a relatively low cost technique. In turn, in the article they validate the technique by measurements using LC-MS/MS. From my perspective, the results of such validation should be included in both the conclusion and the abstract. 

2.- There is an error on Figure 5. Probably the caption of b) corresponds to image c) and caption c) corresponds to image b). 

3.- Regarding meshing (section 2.2.2), information on the mesh independence study should be included. 

4.-  Check the references on lines 280-283. In particular I fail to understand whether "The authors" refers to reference 45 or 47 in the sentence:  "The authors showed 281 that when the advancing angle (θa) for water on nylon fibres is approximately 71° [47], the 282 threshold capture velocity for θa <90° can be obtained as follows [45]"

5.- What is the type of injection used for the droplets, single point or evenly distributed over the inlet surface?

6.- Sentence of lines 161-162 should include a reference.

7.- Indent of lines 183, 216 and 249 should be removed.

8.- Format of DV10, DV50 and DV90 in Line 510 should be the same of the rest of the text (Dv10, Dv50 and Dv90)

Question for the authors:

9.- Regarding the rpm of the ADS, it can be reduced? Since the collection efficiency is reduced at higher wind speed maybe a reduction on the ADS rpm could increase the collection efficiency. 

Author Response

Thanks for your constructive suggestions and comments. We have revised our manuscript. Please see the attached file, our point-by-point response to the reviewer's comments.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper describes an approach to determine capture efficiency of nylon screens in the presence of spray droplets. The paper further examines the importance of CFD modelling to predict capture. This work is well written and would add value; however, a few points should be addressed before publication.

In general, the authors should speak about the limitations of conducting experiments in a wind tunnel. Wall effects, nozzle positioning and the lack of variation in wind speed/airflow typical of an outdoor setting. They should also describe where future work would be needed to overcome or attenuation the impact of these limitations. 

Line 2 (Title): Airborne not needed. Spray drift implies airborne.

Line 103: The XR 11002 at 0.3MPa (~43psi) will produce a fine spray per the manufacturer.  https://www.teejet.com/-/media/dam/agricultural/usa/sales-material/catalog/broadcast_nozzles.pdf#page=6. Is there any justification for using this nozzle? Why not consider other nozzles?

Lines 101 and 105: Authors should explain the importance of the small spraying section of the chamber and small collection section of the chamber. ISO 22856 provides guidance for wind tunnel design and layout, was this standard followed? If not, what is the overall implication?

Authors to consider the wall effects on the drift particles

Lines 163: While it is convenient to measure drift “alongside farmers’ applications”, spray drift measurements can be carried out in fields established with similar layout and crops for experimental studies to represent typical farming practices and areas.

Lines 202-203 reference needed to corroborate the 3 m/s limit. In the US, for example, 4.5 m/s is permitted with other contingencies.

Lines 205: “Spraying was continued for another 10s seconds to ensure that all the airborne droplets had escaped from the drift tunnel” – Do the authors mean that air flow, instead of “spraying”, was maintained for an additional 10s after the 10s spray event?

Line 209: replace for with “as a”

General comment: If an active ingredient is not included in the formulation, a dye could have easily been used considering this work was conducted in a wind tunnel. The TOC method is handy but seems overly complicated without any obvious benefit. Also given the non-use of a pesticide active ingredient, it is not clear the value Lines 161-167 adds. The authors can simply state the method used to analyze the samples collected.

Line 222: Replace “repeated” with “conducted”.  

Lines 274-276: 870 µm is well beyond the VMD range for a medium spray (226 – 325 µm), and well beyond a fine DSD. How important is this to the modelling results?

Lines 350-351: An interesting simulation would be to use the measured DSD for the Teejet nozzles used in the wind tunnel as a benchmark. Also, why were the 17 droplet diameters and 40-360um range selected?

Line 383: What standard was used to characterize the droplet spectrum? If ASABE S-572.1?

Line 385: A VMD of 148um is a fine spray

Author Response

Thanks for your constructive suggestions and comments. We have revised our manuscript. Please see the attached file, our point-by-point response to the reviewer's comments.

Author Response File: Author Response.docx

Reviewer 3 Report

comments see attached file

Comments for author File: Comments.pdf

Author Response

Thanks for your constructive suggestions and comments. We have revised our manuscript. Please see the attached file, our point-by-point response to the reviewer's comments.

Author Response File: Author Response.docx