Staggered-Phase Spray Control: A Method for Eliminating the Inhomogeneity of Deposition in Low-Frequency Pulse-Width Modulation (PWM) Variable Spray

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper deals with the study a low frequency PWM controlled spraying system. The difference between phase and staggered activation are studied through pressure control, droplet size and deposition quality. The methodologies are well documented and are adapted, however, this paper is too superficial, demonstrates evidences and does not go enough into details. Some basic information are missing (pressure sampling frequency, …).

PWM controlled systems were thoroughly studied and commercial systems are available on the market. In general, they are all based on staggered phase principle with the logical argument of the pressure variation limitation. The novelty of this paper is then limited.

The studied system is only 5 Hz (some tests up to 11Hz) as commercial ag-spray system may work under 20 Hz (Teejet Dynajet) or 30 Hz (Raven Hawkeye), or sometimes more. Are all these results basically transferable to higher frequencies?  What would be the interest of working at low frequency ?

Differences between the two phase controls are globally limited in terms of flowrate, droplet and deposition variability.

Most of the results are obtained with a 50% duty cycle but there is no certitude that they can be extended for all duty cycle

Detailed comments

P5 line 194 Fig 3 : were differences really expected between the two control systems ?

Page 6 Table 1 : what is the reflow ratio exactly ? It is not very clear what the control check is supposed to verify.

Page 6 line 201 :  It is not clear what’s the frequency of the pressure monitoring ?

Page 9 line 298 – 302: What are the hypotheses to define the position of the filter papers –in a row and between rows) ? Continuous samplers (bands of filter papers) would avoid this problem   and would help to better define transition zones and eventual zebra. A rapid calculation give (2 m/s – 50% DC – 5 Hz) give a sprayed are of 20cm (along the travelling direction) and a non-sprayed area of 20cm for a given nozzle.  Where does this distance of 7cm (Fig 6a) between filter papers comes from?

Page 9 line 303 : tracer instead of tracker ?

Page 10 Table 2: In the case of the CK, the calculation was based on all pressure values in a steady state condition or also including the switch on and off of the valve?... If I well understand, these pressure fluctuations come from the pump directly (since there is no pressure pneumatic damper) ?…

Page 10 line 342 : Table 1 or Table 2? I

Page 11 Fig 8 : Why the average pressure is different between CK and 2 phase controls?  A deeper frequency analysis would show the pulsations due to the pump but also secondary order frequencies for phase – control situations (small fluctuations on red and blue signal).

Page 12 Fig 9 : Is there a digital monitoring of the solenoids connected to the valve? This would also help to understand any difference between those signals. Are we sure the average pressure was similar for all DC ? there is no information about any replicates ?

Page 13 Fig 10: the point at 9 Hz looks an outlayer. Any evidence of replicates for this experiment?

Page 13 fig 12: This kind of figure shall be avoided since it is confusing : Nothing can relate the points (discrete measurements) and X axis corresponds to different types of conditions. Excepted 1 Point, it can be concluded that the fluctuations are only due to the phase control…That is an evidence.

Page 14 Fig 13: This kind of figure does not provide any valuable information.

Page 14 Table 5 I guess the velocity is an average, why not showing the velocity distribution as for droplet size ?

Page 16 Fig 14 : It would have been interesting to show the deposition profile along a row of collectors instead of average. It is not obvious to show collector number related to Fig6a   

Page 16 Line 496 : title 44. Shall be under Table 7.

 

Author Response

 

 

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In their manuscript, the authors developed a staggered-phase driving spray system, which improved the atomization effect and reduced the pressure fluctuation. In general, the manuscript is well organized and kept focused on the topic. The full length of the paper is adequate, main findings are clearly presented and discussed. Then, I can recommend it for publication in Agriculture after minor revision.

My comments are:

The staggered-phase driving spray system mainly reflects the stability of the system. When it comes to precision agriculture, it needs to be discussed or cited in the introduction.

In addition, many details in the manuscript can be modified by referring to the format of the Agriculture template.

Lines 20,265,447 did not set the first line indentation; 287, 322, and 331 do not need the first indent.

Figures 11 and 12. The Hz unit case in the line chart is consistent with that in the text.

Figure 11. Between different factors of abscissa, the line chart should be disconnected.

Lines 424. Is the conclusion correct?

Lines 489. International standard unified capital initials

There are still many words with no space between spellings.

Therefore, the manuscript needs to carefully modify the details. Too many details are easy to mislead the reviewers to write unprofessionally.

Comments on the Quality of English Language

The language of the manuscript is highly professional, and the English expression is clear. It needs minor repairs to ensure the correctness of spelling.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The present manuscript aims to investigate and propose a method for eliminating the inhomogeneity of ground deposition in low-frequency PWM variable sprays based on a staggered phase drive mode. These presented results provide a better understanding of the droplet spectrum and atomization process to reach optimum operational parameters. They revealed that the PWM control parameters significantly affected the upstream pressure fluctuation (initial pressure > duty cycle > frequency). Also, Staggered-phase spray control could effectively reduce the inhomogeneity of deposition in low-frequency. The manuscript is well written, and the quality can be accepted after revision and modifications. In sum, in this sense, I recommend publishing this manuscript after a minor revision.

1- In the abstract, it is better to improve some sentences and focus more on the innovation and achievement of the paper that comprise it from other similar work.

2- The abbreviation of PWM must be defined when it is presented in the title, abstract, and draft body.

3- If possible, just modify the sentence to a better way of expression, “At an initial pressure of 0.3 MPa, a solenoid  valve frequency of 5 Hz, and a duty cycle of 50%, the pressure fluctuation amplitude upstream of  the nozzle of the PWM variable spray system with the staggered phase drive was reduced by 40.91%, and the dispersion rate of the pressure fluctuation was reduced by 62.78%.”

5- The introduction is written well, but the lack of consistency in the story’s narration is apparent. If possible, please improve it. Add some updated missing references, for instance, the recently published review paper on spraying, “Review of coating and curing processes: Evaluation in automotive industry” https://doi.org/10.1063/5.0109376. This critical and updated reference is missing. Also, powder spray: https://doi.org/10.1016/j.powtec.2019.10.084; Spraying material charging and process of electrostatic spraying: https://doi.org/10.1063/5.0156571

6- In Fig. 1, the schematic visualization is nice, with some arrows just emphasizing the differences between nozzles.

7- Please review the paper again and improve and correct sentences in terms of grammar as you can.

Comments on the Quality of English Language

The manuscript is well written, and the quality can be accepted after revision and modifications. In sum, in this sense, I recommend publishing this manuscript after a minor revision.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for this revised version that provides some improvements. However the paper is (still) not very convincing on the  novelty of this reasearch since PWM valves are known for decades in agriculture.

- the choice of a 5 Hz valve is still not very clear. Advantages are not clearly visible (the price?)... what kind of advantages are expected exactly?

- most of the results are still highly predictible...

- The droplet size part is still to be reviewed the ex Table 5 is missing ! so there is no possibility to get the distribution data anymore...

- There is much place occupied by the results and discussion on the RS that is very secondary to my opinion.

 

 

Author Response

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Author Response File: Author Response.pdf