A New Method of Selecting the Airlift Pump Optimum Efficiency at Low Submergence Ratios with the Use of Image Analysis
Round 1
Reviewer 1 Report
I would like to recommend this manuscript to be considered for publication once the following have been addressed( 1-13):
Can the authors compare their research findings with some numerical studies as mentioned in line 38 and 39 ? I was not convinced that comparisons were made to numerical studies. This can be improved.
2.On page 2 line 45, ..... with the use of four air distributor geometry.......
3. line 67 should this be ... in pipes bends?
4. On page 8, rhog and rhoL should be defined in nomenclature section.
5. On page 9 of 19, line 221, ....criterion that fulfills this assumption......
6. Line 230 define rhoL
7.Line 307 .... of the applied method is a wide range of flow patterns.
8.Line 327...... presented method fulfills.......
9. Line 343..... the selection of optimum gas flow rates is presented in Figure 8.(Omit 'an')
10 Line 369 rewrite .....not always is the maximum efficiency of the pump synonymous with.....
11 Line 406 gravitational acceleration is in m/s^2( check units)
12 In Nomenclature section, define rho2F.
13. In line 452 you write , Int J. Multiphase Fl and in line 474 you write ......Flow. Should choose correct one.
Author Response
Reviewer #1 Comments and answers: The review contained many useful comments and corrections which were helpful to improve the quality of the paper. We have carefully considered all the issues mentioned in the reviewer’s comments and below we referred to the comments point by point:
I would like to recommend this manuscript to be considered for publication once the following have been addressed( 1-13):
Can the authors compare their research findings with some numerical studies as mentioned in line 38 and 39 ? I was not convinced that comparisons were made to numerical studies. This can be improved. [This is very good point and this is the material for a completely new and interesting article. In this work we just signalize that this is important field of knowledge and we conduct research of low submergence ratio while all other research is according to high submergence ratio. That’s why we did not compare to numerical research but focused on the experiment]
2.On page 2 line 45, ..... with the use of four air distributor geometry....... the necessary changes in the text applied
3. line 67 should this be ... in pipes bends? the necessary changes in the text applied
4. On page 8, rhog and rhoL should be defined in nomenclature section. the necessary changes in the text applied
5. On page 9 of 19, line 221, ....criterion that fulfills this assumption...... the necessary changes in the text applied
6. Line 230 define rhoL the necessary changes in the text applied
7.Line 307 .... of the applied method is a wide range of flow patterns. the necessary changes in the text applied
8.Line 327...... presented method fulfills....... the necessary changes in the text applied
9. Line 343..... the selection of optimum gas flow rates is presented in Figure 8.(Omit 'an') the necessary changes in the text applied
10 Line 369 rewrite .....not always is the maximum efficiency of the pump synonymous with..... the necessary changes in the text applied
11 Line 406 gravitational acceleration is in m/s^2( check units) the necessary changes in the text applied
12 In Nomenclature section, define rho2F. the necessary changes in the text applied
13. In line 452 you write , Int J. Multiphase Fl and in line 474 you write ......Flow. Should choose correct one. the necessary changes in the text applied
Reviewer 2 Report
Please see the attached file
Comments for author File: 
Comments.pdf
Author Response
Reviewer#2 Comments and answers: The review encloses numerous relevant comments that made it possible to improve the quality of the manuscript. Below we have addressed all comments in detail:
1. Relevancy: The paper is relevant to the scope of Energies.
2. Originality: The paper is original.
3. Major Comments:
The authors conducted an experimental study on the optimization of two-phase flow in an airlift pump, by applying a known optical method to translate the gray level of a digital image to flow characteristics.
Unfortunately, the paper is poorly written, both technically and linguistically. I would expect a major English editing before accepting the paper. The manuscript was read by native English speaker and all errors have been pointed out and corrected.
There are many unclear declarations throughout the paper. Few examples are:
o P.2-ln#78 – "Despite similar flow parameters of both phases..." What do the authors mean by that? [This is very good point and our thought was badly formulated, the necessary changes in the text applied]
o P.7-oln#168 – The Zuber-Findlay" method is mentioned but not explained. Although the authors refer the readers to the appropriate paper, it is recommended to add a few lines of explanation, as the authors did on the following page, with the Lockhart-Martinelli method. the necessary changes in the text applied. Also we referenced the work where deeper graphical explanation of the Zuber-Findlay method is presented.
o Eq.(1): W'TS is the dimensionless coefficient for plug movement in a stationary liquid. It appears in the void fraction expression as if it is always relevant. What about the case where no plugs occur? How would the reader know not to include it? This coefficient is related to fluid properties and channel geometry and its value is independent of flow parameters and thus flow regime.
o Eq.(2)&(3): wLo & wGo appears without any reference or specification, not within the text and not as a separate equation. [Due to the fundamental nature of these concepts, they are deliberately not described in the text and only a brief description in the nomenclature is given. This values come from the phase flux related to the cross-sectional area of the channel]
o Eq.(16): If the notion of maximal difference in the phases energy as a means of optimization is not a new idea, it is recommended to mention some other methods of optimization that were conducted in a similar manner. I want to stress that the idea of using them as a means to optimize the operation of an airlift pump is good, in my opinion, however, as I believe it leans on similar approached (again, very acceptable), that the authors will do right to mention it to the reader. [This is true. The proposed method is not new in general, whereas in the case of optimization of the airlift pump has not been described so far in the literature. This was highlighted in the revised text]
Throughout the paper, there is sever inconsistencies in symbols. Again, few examples are:
o RG is being used for representing the void fraction. Within the text P.7- (ln#166) it appears as "RG", but within the equations it appears as "RG" (G as a subscript). the necessary changes in the text applied
o The same for G & L on p.8. the necessary changes in the text applied
o The nomenclature seems to be lacking of a specific order. It is not ordered by alphabetic order, neither by separation of Latin and Greek symbols. the necessary changes in the text applied
o There are several duplicities within the nomenclature (p, hp). the necessary changes in the text applied
o On the nomenclature, the pressure appears with small "p", while within the text and equations, it appears as a capital "P". the necessary changes in the text applied
o Eq.(14) & Eq.(17) –Is & s the same? [This is not the same. {eta} is for overall efficiency of the airlift pump. {etas} is for efficiency of the compressor, the necessary changes in the text applied]
o P.12-ln#293- two-phase flows are often referred to as 2P, rather than 2-F. the necessary changes in the text applied
Figure 1 contains three figures that are identical, apart from the different height of the immersion depth. It is my opinion that on one hand, the readers would be able to understand that there are a number of possibilities by viewing only one figure, and on the other, they would benefit from the lack of duplication. [We tried to place all in one figure, but in our opinion it is less readable. We attach the figure 1 for the reference. Of course if You insist on the change we will do it].
4. Publication.
The authors suggest applying a digital image processing method to the analysis of the gaseous and the liquid phases. They offer a way to apply it, and by that they enrich the optimization inventory methods for an airlift pump. This idea, to the eyes of the present reviewer is worth a publication. However, the paper should undergo thorough improvements; some of them were suggested in the present review report.
Accepted with major changes.
Author Response File: Author Response.pdf
