Droplet Entrainment in Steam Supply System of Water-Cooled Small Modular Reactors: Experiment and Modeling Approaches
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper presents a comprehensive study of the previous research of droplet entrainment in steam-flow. The main quality of this research is both experimental and numerical investigation and analysis of the advantages and disadvantages of these approaches.
The paper is well written, easy to read and understand. In my opinion, this paper can be published in your paper, I have only some comments which can contribute to better understanding and presentation of the performed study.
Comments:
1. Summarize of the role of this study in steam generation processes.
2. Emphasize key findings and trends from recent studies.
3. Please, add the significance of the future directions for research.
4. Please, explain and analyses the advantages and disadvantages of developed approaches. Esspecial different cfd models used for simulations.
5. What were the specific challenges in these methods? Why is so difficult to develop numerical models?
6. Identify trends and gaps in current research.
7. What are the challenges in validating numerical simulations against experimental data?
Comments on the Quality of English Language/
Author Response
Comment 1: Summarize of the role of this study in steam generation processes.
Response 1: Thank you for this suggestion. I believe my addition is an improvement. Page 3, line 113.
Comment 2: Emphasize key findings and trends from recent studies.
Response 2: This was a useful recommendation. I have added a paragraph covering comments 2 and 6 starting on page 9, line 389.
Comment 3: Please, add the significance of the future directions for research.
Response 3: A summary section was needed here. I added a short paragraph on page 17, line 652.
Comment 4: Please, explain and analyses the advantages and disadvantages of developed approaches. Esspecial different cfd models used for simulations.
Response 4: I was missing this kind of summary paragraph. It is now included on page 14, line 519
Comment 5: What were the specific challenges in these methods? Why is so difficult to develop numerical models?
Response 5: I included this feedback in the same paragraph as the previous suggestion. Starting on page 14, line 519
Comment 6: Identify trends and gaps in current research.
Response 6: This was a useful recommendation. I have added a paragraph covering comments 2 and 6 starting on page 9, line 389.
Comment 7: What are the challenges in validating numerical simulations against experimental data?
Response 7: I think this adds to the value for people that can learn with this paper. I have added a section starting on page 13, line 461.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper presents no new original experimental or numerical research. Instead, it is more like a review paper, which aims to identify knowledge gaps in experiments and modeling of droplet entrainment in steam supply system of water-cooled small modular reactors. While the paper is certainly useful, some important aspects of entrainment are not discussed. My recommendation is a minor revise, which takes into account the comments listed below.
1. In the introduction, a sketch would be helpful which illustrates the phenomenon of entrainment; at least a connection should be made to Fig.1 and Fig. 2.
2. Entrainment of droplets into a gas stream is always connected to the presence of a continuous liquid phase near a wall. There is not only entrainment of droplets in the gas phase, but entrained droplet can also merge with the continuous phase, a process known as deposition. Therefore, the net rate of entrainment and deposition matters, at least for annular two-phase flow. The authors do not discuss the possibility of deposition, but should.
3. The authors should add citations to some standard references on the topic, such as L. Pan, T.J. Hanratty, Correlation of entrainment for annular flow in horizontal pipes, Int. J. Multiph. Flow, 28 (2002) 385-408.
4. In line 141 the authors state that they limit the paper to transport through a horizontal pipe. What is the reason for this? Are horizontal pipes more important than vertical pipes for SMRs?
5. A further important difference is if the two-phase flow is concurrent or countercurrent. This aspect is not discussed in the paper.
6. In line 150 mist flow is mentioned. But mist flow is not included in Fig. 1. Therefore, it should be explained.
7. Table 1: Are there mathematical relations between E_fg, S_E and Gamma_E and with e defined in Eq. (1)?
8. Subsection 3.5 should not be italic style.
9. In author contributions X.X., Y.Y. and Z.Z are meaningless.
Author Response
Comment 1: In the introduction, a sketch would be helpful which illustrates the phenomenon of entrainment; at least a connection should be made to Fig.1 and Fig. 2.
Response 1: I definitely agree with this. It's much easier to illustrate it than to rely on text description. A new Figure 1 has been added and copyright permission attached in the non-published material.
Comment 2: Entrainment of droplets into a gas stream is always connected to the presence of a continuous liquid phase near a wall. There is not only entrainment of droplets in the gas phase, but entrained droplet can also merge with the continuous phase, a process known as deposition. Therefore, the net rate of entrainment and deposition matters, at least for annular two-phase flow. The authors do not discuss the possibility of deposition, but should.
Response 2: Thank you for your comment. This concept is discussed some in section 2.1.2 but I think there is a need for explicitly naming deposition here. Page 5, line 205
Comment 3: The authors should add citations to some standard references on the topic, such as L. Pan, T.J. Hanratty, Correlation of entrainment for annular flow in horizontal pipes, Int. J. Multiph. Flow, 28 (2002) 385-408.
Response 3: Thank you for the recommendation. This reference has been added to Table 1.
Comment 4: In line 141 the authors state that they limit the paper to transport through a horizontal pipe. What is the reason for this? Are horizontal pipes more important than vertical pipes for SMRs?
Response 4: This is becuase I wanted to narrow the focus of the paper. Two major design basis accidents are the main steam line break and double ended guillotine break of the cold leg near the RPV. Both of these areas would be horizontal piping so I wanted to restrict the focus.
Comment 5: A further important difference is if the two-phase flow is concurrent or countercurrent. This aspect is not discussed in the paper.
Response 5: There was definitely a need to discuss the distintion between these. I have added a paragraph on page 10, line 376.
Comment 6: In line 150 mist flow is mentioned. But mist flow is not included in Fig. 1. Therefore, it should be explained.
Response 6: I agree there was a need for this. I added a sentence before the flow regime figure on page 4.
Comment 7: Table 1: Are there mathematical relations between E_fg, S_E and Gamma_E and with e defined in Eq. (1)?
Response 7: These are intended to be distinct. The Eq. 1 has a lowercase e and is a different variable and distinct from the uppercase E.
Comment 8: Subsection 3.5 should not be italic style.
Response 8: Yes, certainly. Thank you for pointing this out. It has been corrected.
Comment 9: In author contributions X.X., Y.Y. and Z.Z are meaningless.
Response 9: I completely forgot to go back to this section. Apologies for the lack of attention here. It has been addressed.
Reviewer 3 Report
Comments and Suggestions for AuthorsComments are given in attached file.
Comments for author File: 
Comments.pdf
Author Response
Comment 1: In the first sentence of Section 3.2 the authors state “A large proportion of previous droplet entrainment experiments have been performed with a non-condensable gas (NCG) like air to simulate boiling and liquid entrainment in steam.” I would suggest to reformulate this sentence slightly in regard to the boiling features as given in the following. The boiling is a complex phenomenon which involves plenty of mechanisms such as bubble nucleation, bubble growth, detachment from the heating surface, heat and mass transfer at the vapour-liquid interface, etc. These mechanisms cannot be represented by an air-water flow. On the other side, different two-phase mixture flow regimes of interpenetrating vapour and the liquid phases can be simulated by an air-liquid mixture for simplicity.
Response 1: This is an important clarification to make for readers. I should be clear about what this air/water accomplishes and what it lacks. I have made the changes in a new paragraph to begin section 3.2 on page 6, beginning on line 257.
Comment 2: Table 1 gives three correlations of Kataoka et al. in column Correlations and have three entries in column Applicability. Does it mean that the applicability of each correlation is related to an entry in the column Applicability. When Yes, please indicate.
Response 2: There was certainly a need for clarity here. I have added i, ii, and iii indicators in the Kataoka section of Table 1 starting on page 7.
Comment 3: Please, pay attention that variables used in relations in Table 1 are consistent. Here I give some examples where it can be done.
Response 3: Thank you for pointing this out. It is important to clear up confusion for readers.
Comment 3.1: There is the term dimensionless superficial gas velocity (denoted by jg* in correlations by Kataoka et al., 1983) and the term normalized gas velocity (denoted by j* in correlation of Ouallal et al., 2021): Are they the same? When not, please explain how scaling i.e. normalization is done.
Response 3.1: These are in fact the same. I have standardized the notation.
Comment 3.2: I noticed similar inconsistency for h*.
Response 3.2: These variables are the same. I have removed the language that could cause confusion.
Comment 3.3: What do you mean with “above the pool surface” and “above the pool”?
Response 3.3: These are the vertical distance above the surface of the pool.
Comment 3.4: In the third relation of Kataoka et al. you use h and DH (without star to denote scaling). Is that correct?
Response 3.4: Yes, these are correct. They have the same units so the exponent is still dimensionless.
Comment 3.5: How the dimensionless variables are formulated? For example, in relation of (Bae et al., 2019), what is the relation between D and D*?
Response 3.5: These certainly needed a definition for completeness. I have added several equations below the table for the dimensionless variables used.
Comment 3.6: In the row with correlation of (Bae et al., 2019), please write “Weber” with capital W.
Response 3.6: Thank you for pointing this out. It has been corrected.
Comment 3.7: In column Uncertainty and row in which correlation of Ouallal et al., 2021 is given, please do not use coding style to give numbers which involve powers of 10.
Response 3.7: You are absolutely correct and I think it looked sloppy. This has been fixed.
Comment 4: It seems that the height of water level in a pool plays an important role in creating droplet entrainment. Could you give some explanations about phenomena underlaying this dependance?
Response 4: Yes, this would be a good addition. I have added several sentences on page 9, line 336.
Comment 5: In Table 2, what do you mean with NP:NP?
Response 5: There was some ambiguity in this table. I have added some indicators to show the relation between the columns. NP is defined just below the table. It means the information was not provided by the authors.
Comment 6: In Table 3, in column Wire mesh sensors (WMS) (Tompkins et al., 2018) please indicate the meaning of subscripts (i,j,k) and superscripts (meas, lo).
Response 6: This was missing. I have added their meanings in that location of the table.
Comment 7: I would suggest using less abbreviations as it makes difficult to read the text despite their meanings are given in the table.
Response 7: I agree with this suggestion. I have trimmed down some of the acronyms for more of the obscure ones.
