Downward Annular Flow of Air–Oil–Water Mixture in a Vertical Pipe
Round 1
Reviewer 1 Report
It is a collection of data that is not organized in a scientific way. abstract involves introduction. The authors should run experiments for the purpose of the mentioned title and present it in a proper way.
Author Response
Dear Reviewer,
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This manuscript investigates three-phase flows, in particular the industrially important oil-water-air flows. The content of this paper is of interest for energies. In my opinion, the work merits publication. The paper is clearly presented, the title is appropriate, the conclusions are supported by the contents, and the abstract presents a nice summary.
The authors start by reviewing literature where many important references where found, and only a few where missed as pointed out below. After this literature review the experimental setup is described, which has to my knowledge not been used before. In particular, the author identify new flow patterns of the oil-water-gas mixture as observed in the new experimental rig. The measurements made with this rig are of interest for the community. Table 5 presents are concise summary of these flow pattern. Figure 3 plots the flow pattern as function of the average flow velocity and the oil concentration, and a clear pattern emerges. Characteristic lines in these flow maps show when the flow changes the flow pattern. These flow maps support the understanding of the oil-water-air mixture. Another good point is the development of a new model for the void fraction of the phases. Many such models already exist as the authors review. The authors compare their model with the experimental data from their rig in figure 10. The agreement between their theoretically predicted model for the oil, gas, and water void fractions and the corresponding measured data is good. The majority of the measurements is within 30% of their predictions. I am not aware of other studies investigating oil-water-gas mixtures in a vertical pipe.
However, the authors should consider a few minor remarks.
In the introduction: I am missing a few important references. Appropriate references in the introduction are also the recent review by L. Edwards, D. Dhanpat and D. P. Chakrabarti (2018) Hydrodynamics of three phase flow in upstream pipes, Cogent Engineering, 5:1, DOI: 10.1080/23311916.2018.1433983 and references therein
and
Edwards, L., Jebourdsingh, D., Dhanpat, D., & Chakrabarti, D. P. (2018). Hydrodynamics of air and oil–water dispersion/emulsion in horizontal pipe flow with low oil percentage at low fluid velocity. Cogent Engineering, 5(1), 1494494. https://doi.org/10.1080/23311916.2018.1494494
Line 59 An appropriate reference discussing several of these challenges is M Salewski and L Fuchs (2007) International Journal of Multiphase Flow 33 (4) 394-410. https://doi.org/10.1016/j.ijmultiphaseflow.2006.09.007
Title: “in a vertical pipe”
Line 18 “The oil density”
Line 20 “of the void fraction”
Line 72 It is unclear what you mean by “Cognitive areas”. Could you rephrase that.
Line 137. “installation. A diagram…”
Line 163 It is unclear which specific patterns were formed here. Could you elaborate or remove it here and first explain in the section on flow patterns.
Line 204 Consider if you want to rename “the superficial velocity” the “average velocity” throughout your manuscript. I am aware of this lingo, but I find the “average velocity” more clear.
Figure 2. Could you enhance the font size. In particular the legend is difficult to read.
In fact, could you carefully go through all figures and ensure that fonts are clearly readable. Figures 4 to 6 is also a little faint.
MAE does not appear to be defined.
Line 498: “study is concerned”
Line 502 “In this respect”
Author Response
Dear Reviewer,
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Reviewer comments are met now. The paper may be published.
