Review Reports

Round 1

Reviewer 1 Report

The paper concerns with the experimental study on the droplet size and charge-to-mass ratio by using an air-assisted electrostatic nozzle. Detailed parameter study was carried, focusing on, such as dependency of mean droplet diameter VDM on air pressure, liquid pressure as well as the applied voltage. The relationship between charge-to-mass ratio and VDM was analyzed and compared with the commonly used Rayleigh limit. Based on the study some optimized process parameters were proposed.

The main purpose of using electrostatic nozzle is to increasing the transfer efficiency (TE), it is however, pity that authors didn’t carry out experiment of TE, which is usually quite easy and the corresponding results could be useful for analysis of the nozzle performance. In addition, following are some remarks that might help the authors to improve the presentation as well as the research work:

1.     Line110: 0.2 bar to 0.6 bar, the air flow rate…from 110ml to 450ml ( I think). How about the liquid flowrate?

2.     Please check the results in Fig.2. The maximum electric intensity on/near the electrode, E= 60 V/m for the applied voltage 3kV, is too low!

3.     For the droplet size measurement, it would be better to add a schematic sketch for the demonstration of measuring position in the spray jet. Since authors put the laser beam quite far away from the nozzle outlet, i.e. 0.8m, the jet shape downstream and the laser beam position should be explained clearly. In case the diameter of the spray jet (round jet or flat jet?) large than the laser beam diameter, a measurement of scanning is necessary, in order to get a full spray size information.  

4.     In 2.5 Laboratory test, a table for the used parameter would be better for reader.

5.     Equation 3: vl and vg are defined based on which surface? What are Ql and Qg, maybe volume of flow rate?

6.     For easy understanding, text from line 200 to 211 about △VDM should be improved, maybe better to draft one or two △VDM in Fig. 5?

7.     Line 261: the △VDM decreases from 0 to 4kV, what does it mean? Again, text about △VDM is not so easy to understand.

8.     For fig. 7(b), VDM is constant by air pressure = 0.6 bar, which means that the liquid breakup occurs mainly due to air flow rate, the effect of the electric force for further breakup is negligible.

9.     In section 3.3, authors mention the corona model.  Corona occurs usually at very high electric field. For your case with 3kV, fig.2 shows the maximal E = 60 V/m that is too low to create corona, please check the results!

10.  Authors discussed about solution relaxation time and atomization time in line298-302. Are there some roughly number? Since water was used in this study, it is well know that water is easy to be charged.

11.  Section 3.4: The negative correlation of CMD to droplet size is well known according to the definition of CMD and the Rayleigh limit. The discussion on this point in this section should be simplified, since this is not new things. It would be better to move the equation (6) and (7), as well as line 324 -333 to the beginning in this section and then to show your results that are identical to the models. However, the detailed relation of CMD to droplet size could be different, such as in Fig.10 (a) that is similar to the Rayleigh limit, Fig.(b) –(d) are different. Are there some explanation?

12. Line 337: No research has been conducted on the air pressure and liquid pressure. What does the sentence mean?

 

13.  Line 360-361: …, the atomization effect because of applied voltage is not obvious or….

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript presented an experimental investigation on the optimization of the existing air-assisted electrostatic nozzles in terms of structural design to obtain a higher charge-to-mass ratio and a smaller droplet size. The effects of liquid pressure, air pressure and applied voltage on the droplet size and charge-to-mass ratio were investigated. Overall this paper contains good experimental work. However, the manuscript contains some significant issues to be addressed, such as:

1.     In section 2.1, the authors use the electric module of ANSYS to study the variation in the electric field strength at the center axis of the annular ring electrode. The summary of this numerical study needs to be included in the manuscript and the software used needs to be referenced.

2.     Is there a particular reason why the choice of material used for the electrode is brass. Is there any other material suitable for this purpose?

3. The manuscript used some abbreviations of technical terms. Those abbreviations must be claimed in full form when it is used for the first time—for example, CMR, VMD, etc. Please, check this appropriately.

4. The whole text should be checked with regard to the comprehensibility and completeness of individual sentences and the tense used.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

1.     In the manuscript, some references used by authors were written in Chinese. Please make a notice in References.

2.     Line 205: … of liquid flow rate…

3.     Line 224: In Fig. 5c and Fig.5d?

4.     Please rewrite 376-377. According to your results (Fig.10), droplet charge coefficients increase within increasing of applied voltages when the applied voltages are smaller than 4 kV. The slightly decrease of droplet charge coefficient by 4 kV is identical to the results in your Figure 9. Although it is interesting, the explanation from authors (maybe corona effect) fails the solid research results, since by corona discharge droplet can be charged again, which is really a complicated phenomenon, and to explain this may be beyond the author’s knowledge.  It is better to show and to point these interesting results and to write a sentence like: Further investigation should be carried out.    

Author Response

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Author Response File: Author Response.pdf