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##### Abstract

Purpose - By modeling and analyzing the two-phase mechanical seal of the fan-shaped groove end face, which is prone to phase change, an effective method to study the flow field of the mechanical seal when both cavitation and boiling exist simultaneously is found. Design/methodology/approach Based on the finite volume method, a fluid model was developed to investigate a two-phase mechanical seal. The validity of the proposed model was verified by comparing with some classical models.Findings - By modeling and analyzing the two-phase mechanical seal of the fan-shaped groove end face, which is prone to phase change, the analysis of the gap flow field of the mechanical seal was realized when cavitation and boiling existed simultaneously.Originality/value - Based on the model proposed for different conditions, the pressure and phase states in the shallow groove sealing gap were compared. The phase change rate between the mechanical seal faces was also investigated.Peer review - The peer review history for this article is available at:

##### Authors

Gao, Wenbin;  Huang, Weifeng;  Wang, Tao;  Liu, Ying;  Wang, Zhihao;  Wang, Yuming

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###### Web of Science Core Collection Citations 
• pre-publication peer review (FINAL ROUND)
##### Decision Letter
2020/06/01

01-Jun-2020

Dear Gao, Wenbin; Huang, Weifeng; Wang, Tao; Liu, Ying; Wang, Zhihao; Wang, Yuming

It is a pleasure to accept your manuscript ilt-12-2019-0537.R2, entitled "Numerical Model of Two-phase Mechanical Face Seal with Shallow Grooves Based on Finite Volume Method" in its current form for publication in Industrial Lubrication and Tribology. Please note, no further changes can be made to your manuscript.

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Thank you for your contribution. On behalf of the Editors of Industrial Lubrication and Tribology, we look forward to your continued contributions to the Journal.

Sincerely,
Prof. Carsten Gachot
Editor, Industrial Lubrication and Tribology
carsten.gachot@tuwien.ac.at

##### Endorsed by
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2020/04/23

##### Endorsed by
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##### Author Response
2020/04/22

Dear Editors and Reviewers,

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Numerical Model of Two-phase Mechanical Face Seal with Shallow Grooves Based on Finite Volume Method” (Manuscript ID: ilt-12-2019-0537). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Due to the limited number of words in this journal, we can't show all the work done and the conclusions we have obtained, so we choose relatively more meaningful and relevant content to express the ability of this model.

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we list the major changes and marked in red in revised paper.

Reviewer #1:
1. Response to comment: (The quality of the figures still needs to be improved. Please work on that.)

Response:
We have reworked the relevant pictures, especially Figures 4, 5 and 6, to make the information expressed more clear and rich.

1. Response to comment: (There is still not much discussion of the obtained results. This also needs to be improved to make your manuscript suitable for publication. The following articles published by the University of Sao Paulo could help you to discuss your results in the light of the current research literature

-- Multi-scale surface texturing in tribology—Current knowledge and future perspectives
-- Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach)

Response:

In the manuscript submitted this time, we have deleted some descriptive information and further interpreted more valuable information. For example, we have physically explained the characteristics of the pressure curve and the differences in cavitation and boiling.At the same time, we have read the two articles mentioned by the reviewers. It is very enlightening after reading. We have listed these two articles as references.

The modification details of the body part are as follows：

（1）Page 8，Line 48：
Delete： Based on the discrete boiling model, Lebeck also conducted a preliminary numerical simulation investigation on the two-phase seals to predict the temperature distribution more accurately (Lebeck, 1978).

（2）Page 9，Line 1：
Add：In recent years, the application and research of relevant models in shallow groove and texture are common (Rosenkranz et al., 2019).

（3）Page 11，Line 32：
Add：It can be seen that when cavitation existed, each radial pressure curve had a long constant segment. And besides the cavitation area, this constant segment contained a zone where no phase change occurred. This is because the upstream and downstream of this zone were connected to cavitation and boiling positions, respectively, which constrained its upstream and downstream pressure at saturation pressure. Moreover, this no-phase-change zone was in the flat dam area without hydrodynamic effects.

Delete：Under all temperature conditions, the maximum value of the pressure occurred in the fluid leaving the groove to enter the weir region, while the peak pressure was the same. In the weir region on the left side, the pressure slowly decreased from the peak, and the gradient of the pressure also gradually decreased. When the temperature was approximately 443 K, the corresponding pressure dropped to the respective saturation pressure levels as the fluid entered the groove area, owing to the cavitation. In the groove, once cavitation occurred, all pressure curves, including that of the 438 K condition, increased to the maximum value in an approximately linear manner.

（4）Page 11，Line 40：
Add: Fig. 5 shows different pressure trends in these two areas.

Delete：The boiling occurred near the outlet. Since the fluid near the outlet was mainly gaseous and was affected by the compressibility of the gas, the radial pressure gradient near the outlet was relatively large.

（5）Page 11，Line 43：
Add： (Rosenkranz et al., 2019). However, in the boiling region, the pressure decreased rapidly in the radial direction to the outlet pressure, and it hardly changed in the circumferential direction.

（6）Page 11，Line 51：
Add：Either cavitation or boiling is a kind of vaporization that occurs under saturation pressure, based on the same mechanism. According to the distribution of the liquid phase volume fraction shown in the figures, it can be seen that the volume fraction of the boiling area was approximately zero, while the cavitation area was always kept above 0.4. The cavitation area was a closed space where vapor-liquid coexisted. Any trend that may cause a local pressure drop will continue to remain at saturation pressure there due to the induced cavitation. The boiling area was an open space where only a small part was in the state of coexistence of vapor and liquid, and the gas produced flowed out from the open low-pressure boundary. Therefore, the region could not continue to maintain the saturation pressure, but fell rapidly.

Delete：Due to the periodic arrangement of shallow grooves on the end face, the hydrodynamic pressure effect existed in the circumferential direction. On the upstream side, the pressure increased, and on the downstream side, the pressure should decrease. Due to the occurrence of cavitation, the pressure in the cavitation area was uniformly the cavitation pressure. Cavitation contained a further drop in pressure in the area and strengthened the hydrodynamic pressure effects.

（7）Page 12，Line 13：
Delete：In the dam zone near the boiling zone, the pressure changed significantly in the radial direction, but not much in the groove zone.

（8）Page 12，Line 17：
Delete：Therefore, under the same temperature change, the change of phase change region was not very significant.

（9）Page 12，Line 19：
Add：The boiling area was not a uniform annular belt, and its width fluctuated in the circumferential direction. This phenomenon was more obvious at lower temperatures, and the width of the boiling area became more uneven. Due to the periodic arrangement of shallow grooves on the end face, there is a hydrodynamic pressure effect. The pressure increases on the windward side and decreases on the leeward side. The unevenness of the phase distribution was caused by the fluctuation of the pressure distribution in the circumferential direction. The occurrence of cavitation upstream in the radial direction prevented the pressure in this area from further decreasing and enhanced the hydrodynamic pressure effect, while also reducing the unevenness of the pressure distribution in the radial downstream. So when the temperature was higher, the shape of the boiling zone was more uniform.

（10）Page 12,Line 52:
Delete: There is also a difference in the phase change rate between cavitation and boiling. Compared with the cavitation zone, the phase change in the boiling zone only vaporizes and is more intense.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.

##### Endorsed by
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• pre-publication peer review (ROUND 3)
##### Decision Letter
2020/03/26

26-Mar-2020

Dear Dr. Huang:

Manuscript ID ilt-12-2019-0537.R1 entitled "Numerical Model of Two-phase Mechanical Face Seal with Shallow Grooves Based on Finite Volume Method" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

The reviewer(s) have recommended major revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

To revise your manuscript, log into https://mc.manuscriptcentral.com/ilt and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision.

You will be unable to make your revisions on the originally submitted version of the manuscript. Instead, revise your manuscript using a word processing program and save it on your computer. Please also highlight the changes to your manuscript within the document by using the track changes mode in MS Word or by using bold or coloured text.

Once the revised manuscript is prepared, you can upload it and submit it through your Author Centre. The deadline for uploading a revised manuscript is 24-Jun-2020 from receiving this email. If it is not possible for you to resubmit your revision within this timeframe, we may have to consider your paper as a new submission.

When submitting your revised manuscript, you will be able to respond to the comments made by the reviewer(s) in the space provided. You can use this space to document any changes you make to the original manuscript. In order to expedite the processing of the revised manuscript, please be as specific as possible in your response to the reviewer(s).

IMPORTANT: Your original files are available to you when you upload your revised manuscript. Please delete any redundant files before completing the submission.

Please note that Emerald requires you to clear permission to re-use any material not created by you. If there are permissions outstanding, please send these to Emerald as soon as possible. Emerald is unable to publish your paper with permissions outstanding.

Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

Sincerely,
Prof. Carsten Gachot
Editor, Industrial Lubrication and Tribology
carsten.gachot@tuwien.ac.at

Reviewer: 1

- The quality of the figures still needs to be improved. Please work on that.

• There is still not much discussion of the obtained results. This also needs to be improved to make your manuscript suitable for publication. The following articles published by the University of Sao Paulo could help you to discuss your results in the light of the current research literature

-- Multi-scale surface texturing in tribology—Current knowledge and future perspectives
-- Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach

Reviewer: 2

The sealing performance of a two-phase mechanical seal with fan-shaped grooves onto the face was studied by using the finite volume method based on a new fluid model. The interesting result showed the cavitation and boiling existed simultaneously. Also the manuscript has been revised according to the comments of the reviewers. Therefore, it is suggested to be accepted.
Reviewer: 1

Recommendation: Major Revision

- The quality of the figures still needs to be improved. Please work on that.

• There is still not much discussion of the obtained results. This also needs to be improved to make your manuscript suitable for publication. The following articles published by the University of Sao Paulo could help you to discuss your results in the light of the current research literature

-- Multi-scale surface texturing in tribology—Current knowledge and future perspectives
-- Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach

Originality: Does the paper contain new and significant information adequate to justify publication?: Please see comments below.

Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Please see comments below.

Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Please see comments below.

Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Please see comments below.

Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Please see comments below.

Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Please see comments below.

Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: Please see comments below.

This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: No, I would not like my name to appear with my report on Publons

Reviewer: 2

Recommendation: Accept

The sealing performance of a two-phase mechanical seal with fan-shaped grooves onto the face was studied by using the finite volume method based on a new fluid model. The interesting result showed the cavitation and boiling existed simultaneously. Also the manuscript has been revised according to the comments of the reviewers. Therefore, it is suggested to be accepted.

Originality: Does the paper contain new and significant information adequate to justify publication?: yes

Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: It cites the relevant references and no significant work ignored.

Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: yes.

Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: yes, the results are true. The conclusions adequately tie together the other elements of the paper。

Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: yes, it does. These implications consistent withthe findings and conclusions of the paper

Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: the communication quetility is high.

Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: yes

This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

##### Endorsed by
Ongoing discussion (0 comments - click to toggle)
##### Reviewer report
2020/03/26

The sealing performance of a two-phase mechanical seal with fan-shaped grooves onto the face was studied by using the finite volume method based on a new fluid model. The interesting result showed the cavitation and boiling existed simultaneously. Also the manuscript has been revised according to the comments of the reviewers. Therefore, it is suggested to be accepted.

##### Endorsed by
Ongoing discussion (0 comments - click to toggle)
##### Reviewer report
2020/02/17

- The quality of the figures still needs to be improved. Please work on that.

- There is still not much discussion of the obtained results. This also needs to be improved to make your manuscript suitable for publication. The following articles published by the University of Sao Paulo could help you to discuss your results in the light of the current research literature

-- Multi-scale surface texturing in tribology—Current knowledge and future perspectives
-- Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach

##### Endorsed by
Ongoing discussion (0 comments - click to toggle)
##### Author Response
2020/02/14

Dear Editors and Reviewers,

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Numerical Model of Two-phase Mechanical Face Seal with Shallow Grooves Based on Finite Volume Method” (Manuscript ID: ilt-12-2019-0537). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

We can't put pictures in the response input box in this paper submission system, so we just submit an another response letter including pictures and some appendixes as a separate file in last submission, but so far you may not see it. Due to the character limit of this journal, we didn't put the appendixes in our article before, but this time in order to answer the questions in more detail, some sections have been added in original article.

In this study, model validation was performed. However, due to the limitation of the number of ILT submissions, the verification of the model, a part of the model deduction, and some discussions of the calculation examples have to be deleted. We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we did not list the changes but marked in red in revised paper.

Reviewer #1:
1. Response to comment: (The new model presented in this manuscript should be validated.)
Response: We had performed a validation of the model. However, due to the limitation of word size when submitting, this part had to be deleted to ensure the completeness and adequacy of the other parts. The validation of the model is now attached as the Appendix 1.

1. Response to comment: (Why do the authors think it is true：
One: the cavitation zone appears to be more susceptible to temperature changes than the boiling zone.
Response: The size of the phase change region is related to the mechanism of phase change, which is related to the local saturation pressure. Considering the Reviewer’s suggestion, in the new manuscript, we have a specific explanation of this issue. The explanation in the manuscript is as follows:
“This is because the temperature directly determines the local saturation pressure, which affects the size of the region where the phase change occurs. In the dam zone near the boiling zone, the pressure changed significantly in the radial direction, but not much in the groove zone. In addition, the phase change in the cavitation zone is caused by the dynamic pressure effect caused by the change of film thickness in the circumferential direction. Meanwhile, there is no circumferential change in film thickness in the boiling region, so it is not affected by the dynamic pressure effect, so the phase change region is almost unchanged in the circumferential direction. Therefore, under the same temperature change, the change of phase change region was not very significant.”

Two: this paragraph only describes that the size of the gradient changes but lack of analysis or explanation.)
Response: Due to the limitation of the number of words, on the basis of the original manuscript, we have trimmed the results of this part of the simulation. In the new manuscript, we have reorganized the structure of the narrative and added analysis and explanation of the phenomenon according to the Reviewer’s suggestion. In particular, it explains from the perspective of the relationship between the pressure gradient and the phase change mechanism and dynamic pressure effect.

1. Response to comment: (Explain the physical meaning of the phase change rate in the model.)
Response: Both cavitation and boiling are phenomena and results caused by phase changes, and the phase change rate is a parameter that reflects the physical nature of both. Therefore, in order to further understand the difference between the two, we considered it valuable to discuss them. In the new manuscript, we discussed this physical parameter and its significance for cavitation and boiling in more depth in the corresponding paragraphs according to the Reviewer’s comments.

Reviewer #2:
1. Response to comment: (The quality of the figures must be improved. They are partially blurred and with not sufficient information.)
Response: As Reviewer suggested that all the cloud pictures and point plots have been remade, and the characters in them have been enlarged.

1. Response to comment: (The presented introduction and state of the art part is poor. Only a few citations from the last years have been used. All other citations are rather old. This does not really reflect a good state of the art part. The authors need to try to be more up-to-date. There is a huge community working on grooves and surface texturing. This should be well reflected in your article.)
Response: It is also limited by the number of words required, and to ensure the integrity of other chapters, we have compressed the references. Under such constrained conditions, because this article aims to introduce a two-phase seal model, we have retained most of the references to the phase change model of mechanical seals, and have discarded those are related to grooves and surface texturing.

2. Response to comment: (The number of equations should be reduced.)
Response: Under the premise of ensuring the completeness of the content, the derivation of the equations in the introduction of the model, especially the elaboration of the algorithm part, has been abridged in the new manuscript.

3. Response to comment: (There is no real scientific discussion in the manuscript. The results are purely described but not discussed neither interpreted.)
Response: As Reviewer suggested that some descriptive paragraphs have been partially deleted, and the chapters for discussion have been purposefully added. The added or modified parts are marked in red.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.

Appendix 1：Model validation
The continuous boiling model and the JFO boundary are classical models for investigating boiling and cavitation. Therefore, these models were compared with the homogeneous models to verify the validity of the proposed model.
First, the continuous boiling model proposed by Yasuna et al (Yasuna et al., 1990). was selected as the comparison object. The examples and parameters provided in the literature are also referred to in this paper, and were calculated using the existing model. In Fig. 1, the discrete points represent the pressure data obtained along the radial direction by previous studies, while the curve represents the result calculated by the model proposed in this paper. As can be seen in the figure, the results are in good agreement.

(a) Pressure

(b) Liquid phase volume fraction
Fig. 1 Comparison of the proposed model with the continuous boiling model (Yasuna et al., 1990)

Payer et al. selected the analysis results for the mechanical seal of a pure water medium based on the JFO cavitation model as the comparison object. In this study, the geometric and operating parameters provided by Payer et al. were adopted. (Payer et al., 1992)
Fig. 2 shows the circumferential pressure and density distribution within the sealing gap at a certain radius. In the circumferential direction, the pressure first increased and then decreased. Because vaporization did not occur in most areas of the fluid film, the density of the homogeneous fluid was equal to the density of the liquid. However, the density of the homogeneous fluid decreased significantly in the region where the fluid film broke and cavitation formed. The minimum value reached approximately 0.85 of the fluid density in the liquid phase, and had a lower constant pressure, which was approximately equal to the local saturated vapor pressure at the operating temperature. Subsequently, the mixture density gradually increased, and corresponded to the re-formation of the liquid film. Generally, by including the pressure and density values at various positions, in addition to the location of the cavitation region, the calculation results obtained by the proposed model were found to be in good agreement with the results obtained by the JFO boundary model.
By comparing the two abovementioned examples, the validity and accuracy of the proposed model was verified for boiling and cavitation problems.

(a) Pressure

(b) Density
Fig. 2 Comparison of the proposed model with the JFO model (Payer et al., 1992)

References

Payvar P, Salant R F. (1992), “A computational method for cavitation in a wavy mechanical seal”, Journal of Tribology-Transactions of the ASME, Vol. 114, pp.199-204.
Yasuna, J.A. and Hughes, W.F. (1990), “A continuous boiling model for face seals”, Journal of Tribology, VOL.112 No.2, pp.266–274.

##### Endorsed by
Ongoing discussion (0 comments - click to toggle)
• pre-publication peer review (ROUND 2)
##### Decision Letter
2020/01/23

23-Jan-2020

Dear Dr. Huang:

Manuscript ID ilt-12-2019-0537 entitled "Numerical Model of Two-phase Mechanical Face Seal with Shallow Grooves Based on Finite Volume Method" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

The reviewer(s) have recommended major revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

To revise your manuscript, log into https://mc.manuscriptcentral.com/ilt and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision.

You will be unable to make your revisions on the originally submitted version of the manuscript. Instead, revise your manuscript using a word processing program and save it on your computer. Please also highlight the changes to your manuscript within the document by using the track changes mode in MS Word or by using bold or coloured text.

Once the revised manuscript is prepared, you can upload it and submit it through your Author Centre. The deadline for uploading a revised manuscript is 22-Apr-2020 from receiving this email. If it is not possible for you to resubmit your revision within this timeframe, we may have to consider your paper as a new submission.

When submitting your revised manuscript, you will be able to respond to the comments made by the reviewer(s) in the space provided. You can use this space to document any changes you make to the original manuscript. In order to expedite the processing of the revised manuscript, please be as specific as possible in your response to the reviewer(s).

IMPORTANT: Your original files are available to you when you upload your revised manuscript. Please delete any redundant files before completing the submission.

Please note that Emerald requires you to clear permission to re-use any material not created by you. If there are permissions outstanding, please send these to Emerald as soon as possible. Emerald is unable to publish your paper with permissions outstanding.

Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

Sincerely,
Prof. Carsten Gachot
Editor, Industrial Lubrication and Tribology
carsten.gachot@tuwien.ac.at

Reviewer: 1

The sealing performance of a two-phase mechanical seal with fan-shaped grooves onto the face was studied by using the finite volume method based on a new fluid model. The interesting result showed the cavitation and boiling existed simultaneously. Therefore, it is suggested that the following issues be considered and revised before the manuscript is accepted to be published:
1. The new model presented in this manuscript should be validated.
2. Why do the authors think it is true：
One: the cavitation zone appears to be more susceptible to temperature changes than the boiling zone.
Two: this paragraph only describes that the size of the gradient changes but lack of analysis or explanation.
3. Explain the physical meaning of the phase change rate in the model.

Reviewer: 2

- The quality of the figures must be improved. They are partially blurred and with not sufficient information.

• The presented introduction and state of the art part is poor. Only a few citations from the last years have been used. All other citations are rather old. This does not really reflect a good state of the art part. The authors need to try to be more up-to-date. There is a huge community working on grooves and surface texturing. This should be well reflected in your article.

• The number of equations should be reduced.

• There is no real scientific dicussion in the manuscript. The results are purely described but not discussed neither interpreted.

In the first round, I will put it on major revision but real changes are necessary to make it suitable for publication in ILT.
Reviewer: 1

Recommendation: Major Revision

The sealing performance of a two-phase mechanical seal with fan-shaped grooves onto the face was studied by using the finite volume method based on a new fluid model. The interesting result showed the cavitation and boiling existed simultaneously. Therefore, it is suggested that the following issues be considered and revised before the manuscript is accepted to be published:
1. The new model presented in this manuscript should be validated.
2. Why do the authors think it is true：
One: the cavitation zone appears to be more susceptible to temperature changes than the boiling zone.
Two: this paragraph only describes that the size of the gradient changes but lack of analysis or explanation.
3. Explain the physical meaning of the phase change rate in the model.

Originality: Does the paper contain new and significant information adequate to justify publication?: The sealing performance of a two-phase mechanical seal with fan-shaped grooves onto the face was studied by using the finite volume method based on a new fluid model. The interesting result showed the cavitation and boiling existed simultaneously.

Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: The physical meaning of the phase change rate was not explained.

Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: 1. yes
2. well designed
3. The new model presented in this manuscript has not been validated.

Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: The new model presented in this manuscript has not been validated.

Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: 1. no, it does not.
2. no.

Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Why do the authors think it is true：
One: the cavitation zone appears to be more susceptible to temperature changes than the boiling zone.
Two: this paragraph only describes that the size of the gradient changes but lack of analysis or explanation.

Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: No, I would not like my name to appear with my report on Publons

Reviewer: 2

Recommendation: Major Revision

- The quality of the figures must be improved. They are partially blurred and with not sufficient information.

• The presented introduction and state of the art part is poor. Only a few citations from the last years have been used. All other citations are rather old. This does not really reflect a good state of the art part. The authors need to try to be more up-to-date. There is a huge community working on grooves and surface texturing. This should be well reflected in your article.

• The number of equations should be reduced.

• There is no real scientific dicussion in the manuscript. The results are purely described but not discussed neither interpreted.

In the first round, I will put it on major revision but real changes are necessary to make it suitable for publication in ILT.

Originality: Does the paper contain new and significant information adequate to justify publication?: Please see comments below.

Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Please see comments below.

Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Please see comments below.

Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Please see comments below.

Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Please see comments below.

Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Please see comments below.

Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: Please see comments below.

This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: No, I would not like my name to appear with my report on Publons

##### Endorsed by
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##### Reviewer report
2020/01/23

- The quality of the figures must be improved. They are partially blurred and with not sufficient information.

- The presented introduction and state of the art part is poor. Only a few citations from the last years have been used. All other citations are rather old. This does not really reflect a good state of the art part. The authors need to try to be more up-to-date. There is a huge community working on grooves and surface texturing. This should be well reflected in your article.

- The number of equations should be reduced.

- There is no real scientific dicussion in the manuscript. The results are purely described but not discussed neither interpreted.

In the first round, I will put it on major revision but real changes are necessary to make it suitable for publication in ILT.

##### Endorsed by
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##### Reviewer report
2020/01/05

The sealing performance of a two-phase mechanical seal with fan-shaped grooves onto the face was studied by using the finite volume method based on a new fluid model. The interesting result showed the cavitation and boiling existed simultaneously. Therefore, it is suggested that the following issues be considered and revised before the manuscript is accepted to be published:
1. The new model presented in this manuscript should be validated.
2. Why do the authors think it is true：
One: the cavitation zone appears to be more susceptible to temperature changes than the boiling zone.
Two: this paragraph only describes that the size of the gradient changes but lack of analysis or explanation.
3. Explain the physical meaning of the phase change rate in the model.

##### Endorsed by
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• pre-publication peer review (ROUND 1)
##### Decision Letter
2019/11/07

07-Nov-2019

Dear Dr. Huang:

Manuscript ID ilt-05-2019-0198 entitled "Numerical Model of Two-phase Mechanical Face Seal with Shallow Grooves Based on Finite Volume Method" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments from reviewer(s) are included at the bottom of this letter.

In view of the criticisms of the reviewer(s), I must decline the manuscript for publication in the Industrial Lubrication and Tribology at this time. However, a new manuscript may be submitted which takes into consideration these comments.

Please note that resubmitting your manuscript does not guarantee eventual acceptance, and that your resubmission will be subject to re-review by the reviewer(s) before a decision is rendered.

You will be unable to make your revisions on the originally submitted version of your manuscript. Instead, revise your manuscript using a word processing program and save it on your computer.

Once you have revised your manuscript, go to https://mc.manuscriptcentral.com/ilt and login to your Author Center. Click on "Manuscripts with Decisions," and then click on "Create a Resubmission" located next to the manuscript number. Then, follow the steps for resubmitting your manuscript.

Because we are trying to facilitate timely publication of manuscripts submitted to the Industrial Lubrication and Tribology, your revised manuscript should be uploaded as soon as possible. If it is not possible for you to submit your revision within a reasonable amount of time, we will consider your paper as a new submission.

I look forward to a resubmission.

Sincerely,
Prof. Carsten Gachot
Editor, Industrial Lubrication and Tribology
carsten.gachot@tuwien.ac.at

Reviewer: 1

- Please combine Figure 1 and 2.
- Please combine Figure 3, 4 and 5.
- The citations used in the introduction are rather old. It is emphasised that the authors also review the latest works in the respective field and include more citations from the last 3 years in order to present an up-to-date state of the art part. In this sense, you may refer to the following review paper, which also addresses effects in mechanical seals among other mechanical components.
Surface texturing in machine elements− a critical discussion for rolling and sliding contacts

• The number of equations should be reduced in the manuscript.

• There is no discussion in the part results and discussion. Not even one citation can be found in this part. The results are mainly described but not discussed and interpreted.

Reviewer: 2

The authors develop a fluid model to investigate a two-phase mechanical seal based on the finite volume method. They analyze the two-phase mechanical seal with fan-shaped groove end face and prove that the cavitation and boiling existed simultaneously.
It is suggested that the following issues be considered and revised before the manuscript is fully accepted to be published, otherwise to be rejected:
1. The model should be validated by experiment or the other published test results.
2. There are some descriptions in the manuscript lack of analysis or explanation. For example：
page 14 of 22, line 56: “This suggests that the cavitation region and the boiling region exerted mutual influence to each other.” What is the mutual influence and what are the causes of mutual influence?
page 15 of 22, line 15: “this suggests that the cavitation was affected more by the temperature changes than by boiling”. What does this phenomenon cause?
Page 15 of 22, line 17-20: this paragraph only describes the sizes of the gradient changes but lack of analysis or explanation. Give it.
3. What is the physical meaning of the phase change rate and what is the significance of this comparison?.
4. page 14 of 22, line 48: “one of them is t an approximately…” the word “t” is redundant or not?

Reviewer: 3

I had the opportunity to review similar versions of this work for two other journals. The paper has been improved in some way: more compact and clear. Howevere there is still an issue that I previously raised in my previous reviews and that pushed me to reject the paper. This issue has not been adressed and the paper cannot be accepted since the results are not correct:
In cavitation area, there is a simple relation between h and rho: hrho = cste.
Using liquid value in the dam and mixture value in the groove where cavitation occurs: rho_l
h0 = rho * (h0+hg). Thus rho = rho_l * h0 / (h0+hg). If it assumed that the gas density is small compared to the liquid density rho = rho_l * alpha _ l. Thus alpha_l = h0 / (h0+hg). Using h0 = 3 µm and hg = 10 µm, it is found that alpha_l must be close to 0.23. This is the value I computed with my simulation software for similar conditions. The authors found 0.35.
There is a problem. It is necessary that the authors compare their results to previous works to check the validity of their approach.
Reviewer: 1

- Please combine Figure 1 and 2.
- Please combine Figure 3, 4 and 5.
- The citations used in the introduction are rather old. It is emphasised that the authors also review the latest works in the respective field and include more citations from the last 3 years in order to present an up-to-date state of the art part. In this sense, you may refer to the following review paper, which also addresses effects in mechanical seals among other mechanical components.
Surface texturing in machine elements− a critical discussion for rolling and sliding contacts

• The number of equations should be reduced in the manuscript.

• There is no discussion in the part results and discussion. Not even one citation can be found in this part. The results are mainly described but not discussed and interpreted.

Originality: Does the paper contain new and significant information adequate to justify publication?: Please see comments below.

Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Please see comments below.

Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Please see comments below.

Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Please see comments below.

Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Please see comments below.

Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Please see comments below.

Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: Please see comments below.

This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: No, I would not like my name to appear with my report on Publons

Reviewer: 2

The authors develop a fluid model to investigate a two-phase mechanical seal based on the finite volume method. They analyze the two-phase mechanical seal with fan-shaped groove end face and prove that the cavitation and boiling existed simultaneously.
It is suggested that the following issues be considered and revised before the manuscript is fully accepted to be published, otherwise to be rejected:
1. The model should be validated by experiment or the other published test results.
2. There are some descriptions in the manuscript lack of analysis or explanation. For example：
page 14 of 22, line 56: “This suggests that the cavitation region and the boiling region exerted mutual influence to each other.” What is the mutual influence and what are the causes of mutual influence?
page 15 of 22, line 15: “this suggests that the cavitation was affected more by the temperature changes than by boiling”. What does this phenomenon cause?
Page 15 of 22, line 17-20: this paragraph only describes the sizes of the gradient changes but lack of analysis or explanation. Give it.
3. What is the physical meaning of the phase change rate and what is the significance of this comparison?.
4. page 14 of 22, line 48: “one of them is t an approximately…” the word “t” is redundant or not?

Originality: Does the paper contain new and significant information adequate to justify publication?: yes

Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Suggestions for these are given.

Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: no

Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Suggestions for these are given.

Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Suggestions for these are given.

Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Suggestions for these are given.

Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: Suggestions for these are given.

This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: No, I would not like my name to appear with my report on Publons

Reviewer: 3

I had the opportunity to review similar versions of this work for two other journals. The paper has been improved in some way: more compact and clear. Howevere there is still an issue that I previously raised in my previous reviews and that pushed me to reject the paper. This issue has not been adressed and the paper cannot be accepted since the results are not correct:
In cavitation area, there is a simple relation between h and rho: hrho = cste.
Using liquid value in the dam and mixture value in the groove where cavitation occurs: rho_l
h0 = rho * (h0+hg). Thus rho = rho_l * h0 / (h0+hg). If it assumed that the gas density is small compared to the liquid density rho = rho_l * alpha _ l. Thus alpha_l = h0 / (h0+hg). Using h0 = 3 µm and hg = 10 µm, it is found that alpha_l must be close to 0.23. This is the value I computed with my simulation software for similar conditions. The authors found 0.35.
There is a problem. It is necessary that the authors compare their results to previous works to check the validity of their approach.

Originality: Does the paper contain new and significant information adequate to justify publication?: Not really, similar approach have been previously published (for example Wang et al. 2014

Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: This is a short litterature review limited to phase change in seals. It can be extended to lubrication problems.

Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Methodology is OK and clear. A comparison to previous work is missing.

Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: From my point of view, there is a problem in the results. See my comments

Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: The authors claim they can deal with cavitation and boiling. But it is limited to isothermal conditions and thus boiling in this case has no interest.

Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: English needs to be improved

Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

##### Endorsed by
Ongoing discussion (0 comments - click to toggle)
##### Reviewer report
2019/11/07

I had the opportunity to review similar versions of this work for two other journals. The paper has been improved in some way: more compact and clear. Howevere there is still an issue that I previously raised in my previous reviews and that pushed me to reject the paper. This issue has not been adressed and the paper cannot be accepted since the results are not correct:
In cavitation area, there is a simple relation between h and rho: h*rho = cste.
Using liquid value in the dam and mixture value in the groove where cavitation occurs: rho_l*h0 = rho * (h0+hg). Thus rho = rho_l * h0 / (h0+hg). If it assumed that the gas density is small compared to the liquid density rho = rho_l * alpha _ l. Thus alpha_l = h0 / (h0+hg). Using h0 = 3 µm and hg = 10 µm, it is found that alpha_l must be close to 0.23. This is the value I computed with my simulation software for similar conditions. The authors found 0.35.
There is a problem. It is necessary that the authors compare their results to previous works to check the validity of their approach.

##### Endorsed by
Ongoing discussion (0 comments - click to toggle)
##### Reviewer report
2019/10/13

The authors develop a fluid model to investigate a two-phase mechanical seal based on the finite volume method. They analyze the two-phase mechanical seal with fan-shaped groove end face and prove that the cavitation and boiling existed simultaneously.
It is suggested that the following issues be considered and revised before the manuscript is fully accepted to be published, otherwise to be rejected:
1. The model should be validated by experiment or the other published test results.
2. There are some descriptions in the manuscript lack of analysis or explanation. For example：
page 14 of 22, line 56: “This suggests that the cavitation region and the boiling region exerted mutual influence to each other.” What is the mutual influence and what are the causes of mutual influence?
page 15 of 22, line 15: “this suggests that the cavitation was affected more by the temperature changes than by boiling”. What does this phenomenon cause?
Page 15 of 22, line 17-20: this paragraph only describes the sizes of the gradient changes but lack of analysis or explanation. Give it.
3. What is the physical meaning of the phase change rate and what is the significance of this comparison?.
4. page 14 of 22, line 48: “one of them is t an approximately…” the word “t” is redundant or not?

##### Endorsed by
Ongoing discussion (0 comments - click to toggle)
##### Reviewer report
2019/10/03

- Please combine Figure 1 and 2.
- Please combine Figure 3, 4 and 5.
- The citations used in the introduction are rather old. It is emphasised that the authors also review the latest works in the respective field and include more citations from the last 3 years in order to present an up-to-date state of the art part. In this sense, you may refer to the following review paper, which also addresses effects in mechanical seals among other mechanical components.
Surface texturing in machine elements− a critical discussion for rolling and sliding contacts