Comparative Study of Droplet Diameter Distribution: Insights from Experimental Imaging and Computational Fluid Dynamics Simulations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This work attempts to study a two-phase flow problem, aka water droplet, through simulation, which is validated against experiment. The topic is related to this journal. This paper is generally well-written and presented. However, the scientific impact of this work and significance is less discussed in the introduction section. Some of the important information is missing, which leads to confusion. Therefore, the current form of the manuscript is not up to the standard of this journal. 

Major comments: 

1. Page 1, graphic abstract. the camera and light source on the simulation is confusing since they are not experiment and therefore don't involve instrumentations.

2. Page 3, "...first instance...," none of the work mentioned in the literature review have combined experiment with CFD? I don't think so.

3. Page 3, "...developing...," did you modify the existing commercial solver or write some of your own code? otherwise, I wouldn't call it developing CFD model

4. Page 7, section 2.2. any mesh information? time step, transient or static simulation, etc? Would it be possible to show the mesh?

5. Page 10, figure 4(b), is the red dot experiment data? if so, how is z measured?

6. Page 10, figure 4(b), is the black line the fit curve of red dot? They don't seem to match well, any reason why? 

7. Page 13, figure 9, is this a snapshot of one moment? Which time moment should be specified.

8. Page 16, conclusion section, any impact on the scientific community?

Minor comments:

1. Page 4, figure 1(b). what does N1H0, N1H1, N1H2 mean? Readers will get confused when they first time see that without knowing what they are.

2. Page 4, figure 1(b), seems like there is water inside the tube already.

3. page 5, equation (1)-(3), (8). What are these variables in the equations. They should be clearly defined.

4. Page 5, table 1, "Flow rate, 1/hr," double-check the unit. How is this controled or measured?

5. Page 5, line 180, "...in total 1000...," what is the frame rate of the imaging system?

6. Page 6, equation (4), within one frame, the size of droplet varies. What is di exactly?

7. Page 6, figure (2), how is the coalescence droplet's diameter estimated? 

8. Page 7, line 216, "...that size..." what size? 

9. Page 7, line 237-line 240, which phase is simulated, and which phase is modeled?

10. Page 11, line 339, "...M1:3.5 mm, ..." what do they mean?

 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attached pdf file. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Figure 1b no detailed description was found in the paper.

2. There are 6 cases in Table 2, but only 4 cases are used in the following study. Are these 4 typical cases in Table 3?

3. On page 10, lines 320-321: "From Figures 4a and 5b, it is clear that quantile-quantile plots fit fairly well with R2 values greater than 0.9. "It is clear that they fitted well with R2 values greater than 0.9. Is there a specific theoretical formula?

4. "Log-normal, Gaussian, or normal distribution" is mentioned on page 3, and "the appropriate log-normal distribution" is used to examine the cases. Is the normal distribution more appropriate for the cases in this paper?

5. Figure 6-8 needs to be supplemented with the legends for Figures a and b.

Comments on the Quality of English Language

English needs further improvement.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attached pdf file. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript focused on the development of a computational fluid dynamics model for predicting the size and distribution of water droplets falling freely in a transparent square tube. The paper fits within the scope of the journal. The following points need to be revised:

1.    Clearly define the specific objectives of the study at the end of the Introduction.

2.    Lines 230/231. „namely the Navier-Stokes equations or Reynolds-Averaged Navier-Stokes (RANS) equation?“ It is not clear here which equations you used, NS or RANS?

3.    The governing equation of flud machanics were not provided!?

4.    What about heat and mass transfer in the mathematical model?

5.    The numerical grid. How big is the error in the grid independence study?

6.    The units have to be written upright in Table 3.

7.    The visibility of Figure 9 need to be improved.

8.    Expand on the Conclusions and state the implications of the study.

 

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attached pdf file. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I am satisfied with the revision and therefore suggest for publication.

Author Response

Thank you for your time effort to review this manuscript and accepting the revision.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have improved their work. Only one issue needs to be addressed before publication, namely: the governing equations of fluid mechanics should be presented as equations in the main text.

Author Response

Thank you for your time and effort to review this manuscript. The governing equations of fluid mechanics in equation form has been updated in the new version of manuscript. Thank you