Abstract

Purpose- The purpose of this study is to determine the sealing performance of face seals by numerical analysis of thermoelastohydrodynamic characteristics of supercritical CO2(S-CO2) spiral groove face seals in the supercritical regime.Design/methodology/approach- The spiral groove face seal was used as the research object. The distribution of lubricating film pressure and temperature was analysed by solving the gas state, Reynolds and energy equations using the finite difference method. Furthermore, the influence law of sealing performance was obtained.Findings - Close to the critical temperature of S-CO2, face distortions produced by increasing pressure lead to divergent clearance and resulted in reduced opening force. In the state of S-CO2, the face distortions generated by increasing seal temperature lead to convergent clearance, which enhances the opening force. In addition, near the critical temperature of S-CO2, the opening force may be reduced by 10%, and the leakage rate of the seal sharply increases by a factor of four.Originality/value- The thermoelastohydrodynamic characteristics of supercritical CO2 face seals are illustrated considering the actual gas effect including compressibility, heat capacity and viscosity. Face distortions and sealing performance were calculated under different seal pressures and seal temperatures in the supercritical regime, as well as with N-2 for comparison.Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2020-0169/


Authors

Zhu, Delei;  Bai, Shaoxian

Publons users who've claimed - I am an author

No Publons users have claimed this paper.

Contributors on Publons
  • 1 reviewer
  • pre-publication peer review (FINAL ROUND)
    Decision Letter
    2020/08/12

    12-Aug-2020

    Dear Zhu, Delei; Bai, Shaoxian

    It is a pleasure to accept your manuscript ilt-05-2020-0169.R2, entitled "Thermoelastohydrodynamic Characteristics of Supercritical CO2 Spiral Groove Face Seals" in its current form for publication in Industrial Lubrication and Tribology. Please note, no further changes can be made to your manuscript.

    Please go to your Author Centre at https://mc.manuscriptcentral.com/ilt (Manuscripts with Decisions for the submitting author or Manuscripts I have co-authored for all listed co-authors) to complete the Copyright Transfer Agreement form (CTA). We cannot publish your paper without this.

    All authors are requested to complete the form and to input their full contact details. If any of the contact information is incorrect you can update it by clicking on your name at the top right of the screen. Please note that this must be done prior to you submitting your CTA.

    If you have an ORCID please check your account details to ensure that your ORCID is validated.

    By publishing in this journal your work will benefit from Emerald EarlyCite. As soon as your CTA is completed your manuscript will pass to Emerald’s Content Management department and be processed for EarlyCite publication. EarlyCite is the author proofed, typeset version of record, fully citable by DOI. The EarlyCite article sits outside of a journal issue and is paginated in isolation. The EarlyCite article will be collated into a journal issue according to the journals’ publication schedule.

    FOR OPEN ACCESS AUTHORS: Please note if you have indicated that you would like to publish your article as Open Access via Emerald’s Gold Open Access route, you are required to complete a Creative Commons Attribution Licence - CCBY 4.0 (in place of the standard copyright assignment form referenced above). You will receive a follow up email within the next 30 days with a link to the CCBY licence and information regarding payment of the Article Processing Charge. If you have indicated that you might be eligible for a prepaid APC voucher, you will also be informed at this point if a voucher is available to you (for more information on APC vouchers please see http://www.emeraldpublishing.com/oapartnerships

    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

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/07/13

    After the content improvements in review loop 1 and the language corrections in review loop 2, I recommend the acceptance of the manuscript.

    Reviewed by
    Cite this review
    Author Response
    2020/06/28

    Dear editor,
    Thanks very much for your letter and the comments about our paper submitted to Thermoelastohydrodynamic Characteristics of Supercritical CO2 Spiral Groove Face Seals (Manuscript number: ilt-05-2020-0169.R1). We have modified the manuscript accordingly by typing in blue color, and detailed corrections are listed below point by point:

    Reviewer #1:
    1) I am satisfied with most of the changes. However, the language of the manuscript still needs to be improved as the flow and readability are poor. Moreover, there are still some spelling mistakes, e.g. p.2 l.21 "Profit et al." instead of "Profito" etc. The authors might want to consider professional english editing.

    Response: Thanks for your comment. we have improved the language of our manuscript by language service on the website app.editage.com.

    Thank you again for the excellent and professional suggestion about our manuscript. The manuscript has been resubmitted to your journal. We look forward to your positive response.



    Cite this author response
  • pre-publication peer review (ROUND 2)
    Reviewer report
    2020/06/21

    No further comments.

    Reviewed by
    Cite this review
    Decision Letter
    2020/06/20

    20-Jun-2020

    Dear Prof. Bai:

    Manuscript ID ilt-05-2020-0169.R1 entitled "Thermoelastohydrodynamic Characteristics of Supercritical CO2 Spiral Groove Face Seals" 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 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 20-Jul-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.

    To help support you on your publishing journey we have partnered with Editage, a leading global science communication platform, to offer expert editorial support including language editing and translation.
    If your article has been rejected or revisions have been requested, you may benefit from Editage’s services. For a full list of services, visit: authorservices.emeraldpublishing.com/
    Please note that there is no obligation to use Editage and using this service does not guarantee publication.

    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(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    I am satisfied with most of the changes.
    However, the language of the manuscript still needs to be improved as the flow and readability are poor. Moreover, there are still some spelling mistakes, e.g. p.2 l.21 "Profit et al." instead of "Profito" etc. The authors might want to consider professional english editing.

    Reviewer: 2

    Comments to the Author
    No further comments.
    Reviewer: 1

    Recommendation: Minor Revision

    Comments:
    I am satisfied with most of the changes.
    However, the language of the manuscript still needs to be improved as the flow and readability are poor. Moreover, there are still some spelling mistakes, e.g. p.2 l.21 "Profit et al." instead of "Profito" etc. The authors might want to consider professional english editing.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Adequate novelty to justify publication.

    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?: An appropriate overview of literature is given and cited.

    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?: The methodology seems to be appropriate and well build.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: The presentation and discussion of results has improved and is now appropriate.

    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?: Implications are consistent with findings/conclusions.

    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 writing and grammar still have 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?: 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. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: No, I would not like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Accept

    Comments:
    No further comments.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: No further comments.

    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?: No further comments.

    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 further comments.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: No further 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?: No further comments.

    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.: No further comments.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: No further comments.

    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. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: No, I would not like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/06/14

    I am satisfied with most of the changes.
    However, the language of the manuscript still needs to be improved as the flow and readability are poor. Moreover, there are still some spelling mistakes, e.g. p.2 l.21 "Profit et al." instead of "Profito" etc. The authors might want to consider professional english editing.

    Reviewed by
    Cite this review
    Author Response
    2020/06/11

    Dear editor,
    Thanks very much for your letter and the comments about our paper submitted to Thermoelastohydrodynamic Characteristics of Supercritical CO2 Spiral Groove Face Seals (Manuscript number: ilt-05-2020-0169). After carefully studying your advice, we have checked the manuscript and revised it accordingly, and the changes of our manuscript are highlighted using the track changes mode in MS Word.

    Reviewer #1:
    1) The paper contains results about face distortions and thermohydrodynamic properties of CO2 spiral groove face seals. However, this was also partly addresses by publications in literature before. Therefore, the research gap that is closed by this manuscript should be better pointed out.
    Response: Thank you for your comment. The third paragraph was added to the Introduction in this manuscript, in order to point out the supplement to the previous research gap. “In this manuscript, thermoelastohydrodynamic behavior of S-CO2 spiral groove face seals are numerically analyzed, as well as N2 as a comparison, considering gas actual effect including compressibility, heat capacity and viscosity. Face distortions and sealing performance are calculated under different seal pressure and seal temperature in the supercritical regime and focused on the influence of the phase change near the critical point about it”.

    2) The presentation of the results sometimes seems somewhat random and needs to be revised. Therefore, it should be explained in more detail why and what is shown in the figures. Therefore, the results should be discussed more than just described.
    Response: Thank you for your comment. The results presented in the figures are described in more detail and discussed, the Results and discussion be revised as follows “The reason for this phenomenon is that the film pressure gradient of the face seal and the phase change of the CO2 transcritical point at the inner diameter make the CO2 expansion and heat absorption, and the different temperature distributions in the cross sections of the stator and the rotor are due to the difference in thermal conductivity.”. (Page 5_L10-13).
    “The reason for this temperature distribution is that the medium enters groove area to expand and absorb heat so that the temperature drops. Then, the pumping effect of the spiral groove makes CO2 continuously compress and release heat at the root of groove, leading to the temperature to rise along the spiral groove”. (Page 5_L19-22).
    “The results are in agreement with previous work by Fairuz (Fairuz and Jakn, 2016), who identified that the viscous effects and the pumping effect of groove lead to the peak pressure appearing at the groove root”. (Page 5_L26, 27).
    “The reason for this phenomenon can be explained by the compressibility and viscosity curves in Figure 2(a) and 2(c). Clearly, when the temperature exceeds the critical point, the compressibility and viscosity gradient of CO2 increase sharply with the increase of temperature. Therefore, the temperature rise of the CO2 film is mainly caused by the friction heat produced by the shear effect, and the shear heat is mainly affected by the viscosity of medium. Additionally, the temperature difference between the inner diameter and the outer diameter of the CO2 film is due to the gas expansion caused by the pressure gradient”. (Page 6_L11-17).
    “It can be explained by the face distortions, In Figure 7, near the critical temperature there is a sharper divergent clearance between sealing surfaces as the pressure”. (Page 7_L3-5).
    “The reason for this phenomenon is, for one thing, from Figure 7, we can see that under the near critical condition, with the increase of pressure, the divergent clearance between the seal faces becomes more and more obvious. For another, the pressure gradient of inlet and outlet increases with the increase of sealing pressure. Surface distortion and pressure gradient leading to great fluctuation of sealing performance and significant increase of leakage rate”. (Page 7_L12-16).

    3) English writing and grammar should be improved, sometimes the sentence structure is confusing. It might be advantageous for the readability to place the sources at the end of the sentences so as not to interrupt the statements.
    Response: Thank you for your comment. The English grammar and writing in the manuscript have been revised, such as some sentences with blue font color. In order not to interrupt the statements, all references have been placed at the end of the sentence.

    Reviewer #2:
    1) The language of the manuscript needs to be revised carefully.
    Response: Thank you for your comment. The English grammar and writing in the manuscript have been revised, such as some sentences with blue font color.

    2) There is a recent review article of the use of surface texturing in mechanical components including seals and their leakage. This article should be included in the introduction and bears an excellent base to further discuss your results. You may want to refer to Surface texturing in machine elements− a critical discussion for rolling and sliding contacts.
    Response: Thank you for your comment. The second paragraph of the Introduction has been revised, “For the surface texture, it has an important influence on the surface lubrication performance. Profit et al have studied the effect of surface texture on the tribological performance under the convergence gap through experiments and numerical approach and the results showed that the surface texture under the convergence gap could reduce the coefficient of friction by 10-15%”. In addition, two references are added as follow:
    (1) Rosenkranz A., Costa H. L., Profito F., Gachot C., Medina S., Dini D. (2019), “Influence of surface texturing on hydrodynamic friction in plane converging bearings - An experimental and numerical approach,” Tribology International, vol. 134, pp. 190-204.
    (2) Profito F. J., Giacopini M., Zachariadis D. C., Dini D. (2015), “A General Finite Volume Method for the Solution of the Reynolds Lubrication Equation with a Mass-Conserving Cavitation Model,” Tribology Letters, vol. 60, no.1, pp. 1-21.

    3) if possible, the number of equations should be reduced. The group around Profito has recently published a review article on numerical approaches in surface texturing. This article may help to largely reduce the number of equations.
    Response: Thank you for your comment. The number of equations has been reduced to five equations, which are the core equations of this manuscript, “Fluid lubrication based on the Reynolds equation has been widely applied in numerical analysis of face seals. Similar to the basic mathematical equations for the numerical simulations of the surface textured slider (Profito et al, 2015; Rosenkranz et al, 2019), for thermohydrodynamic lubrication analysis of face seals, the mathematical model mainly includes Reynolds equation, energy equation, solid heat conduction equation and fluid state equation (Bai and Wen, 2019). Here, for the supercritical fluid lubrication model, the point is the fluid state equation coupled to obtain film temperature and pressure. For gas state, following temperature equation and pressure equation is applied in the analysis (Bai and Wen, 2019).”. (Page 3_L14-21).

    4) There is no discussion in the entire manuscript. Not even one citation can be found in the part results and discussion.
    Response: Thank you for your comment. For the Results and discussion, supplement the sources of the arguments cited in the discussion, “According to Fairuz's research, the ideal gas law is not accurate in predicting the fluid and thermodynamic properties of the CO2 when fluid conditions at the seal inlet, outlet, or within the seal are in the proximity of the critical point (Fairuz and Jakn, 2016). For the actual gas, according to the mathematical model, compressibility, specific heat capacity and viscosity need to be considered, and it is usually impossible to assume that the gas is an ideal gas, the compressibility of actual gas is mainly characterized by the compressibility coefficient (Bai and Wen, 2019)”.( Page 4_L12-17)
    “But for sealing medium CO2, it may happen to convert between supercritical regime and gas regime (Span and Wagner, 1996)”. (Page 5_L4, 5)
    “The results are in agreement with previous work by Fairuz (Fairuz and Jakn, 2016), who identified that the viscous effects and the pumping effect of groove lead to the peak pressure appearing at the groove root”. (Page 5_L26, 27)
    “Surface distortions play an important role in sealing performance for the high pressure face seals due to the elastic distortion induced by high sealing pressure and thermal distortion induced by film temperature variation (Thomas et al, 2007; Bai et al, 2017)”. (Page 6_L3-5)
    “Correspondingly, the face distortions result in an increasing divergent clearance as shown in Figure 7, similar with N2 seal (Bai and Wen, 2017)”. (Page 6_L24, 25).
    In addition, the results presented in the figures are described in more detail and discussed, the Results and discussion be revised as the highlighted part of the font in this section (3. Results and discussion). Such as: (Page 5_L10-13), (Page 5_L19-22), (Page 5_L27, 28), (Page 6_L3-5), (Page 6_L11-17), (Page 7_L3-5), (Page 7_L12-16).

    5) The figures are rather blurred and of poor quality.
    Response: Thank you for your comment. All the pictures of the rather blurred and poor quality are redrawn at a resolution of at least 300 dpi, meet the contribution requirements of the Journal, such as figure 1-3 and figure 8-10.

    Thank you again for the excellent and professional suggestion about our manuscript. The manuscript has been resubmitted to your journal. We look forward to your positive response.



    Cite this author response
  • pre-publication peer review (ROUND 1)
    Reviewer report
    2020/05/27

    • The language of the manuscript needs to be revised carefully.
    • There is a recent review article of the use of surface texturing in mechanical components including seals and their leakage. This article should be included in the introduction and bears an excellent base to further discuss your results. You may want to refer to Surface texturing in machine elements− a critical discussion for rolling and sliding contacts

    • if possible, the number of equations should be reduced.

    • The group around Profito has recently published a review article on numerical approaches in surface texturing. This article may help to largely reduce the number of equations.

    • There is no discussion in the entire manuscript. Not even one citation can be found in the part results and discussion.

    • The figures are rather blurred and of poor quality.

    Reviewed by
    Cite this review
    Decision Letter
    2020/05/26

    26-May-2020

    Dear Prof. Bai:

    Manuscript ID ilt-05-2020-0169 entitled "Thermoelastohydrodynamic Characteristics of Supercritical CO2 Spiral Groove Face Seals" 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-Aug-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.

    To help support you on your publishing journey we have partnered with Editage, a leading global science communication platform, to offer expert editorial support including language editing and translation.
    If your article has been rejected or revisions have been requested, you may benefit from Editage’s services. For a full list of services, visit: authorservices.emeraldpublishing.com/
    Please note that there is no obligation to use Editage and using this service does not guarantee publication.

    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(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    The manuscript is about the numerical analysis of thermohydrodynamic characterisitcs of CO2 spiral groove face seals. The modelling and the results could be of interest to the research community given the complexity of the subject matter of the investigation.
    I therefore recommend acceptance if the mentioned ciritcs regarding the qualitiy communication and the presentation of results are addressed.

    Reviewer: 2

    Comments to the Author
    - The language of the manuscript needs to be revised carefully.
    - There is a recent review article of the use of surface texturing in mechanical components including seals and their leakage. This article should be included in the introduction and bears an excellent base to further discuss your results. You may want to refer to Surface texturing in machine elements− a critical discussion for rolling and sliding contacts

    • if possible, the number of equations should be reduced.

    • The group around Profito has recently published a review article on numerical approaches in surface texturing. This article may help to largely reduce the number of equations.

    • There is no discussion in the entire manuscript. Not even one citation can be found in the part results and discussion.

    • The figures are rather blurred and of poor quality.
      Reviewer: 1

    Comments:
    The manuscript is about the numerical analysis of thermohydrodynamic characterisitcs of CO2 spiral groove face seals. The modelling and the results could be of interest to the research community given the complexity of the subject matter of the investigation.
    I therefore recommend acceptance if the mentioned ciritcs regarding the qualitiy communication and the presentation of results are addressed.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: The paper contains results about face distortians and thermohydrodynamic properties of CO2 spiral groove face seals. However, this was also partly addresses by publications in literature before. Therefore, the research gap that is closed by this manuscript should be better pointed out.

    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 paper discusses an appropriate range of literature sources.

    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?: Numerical modelling seems appropriate.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: The presentation of the results sometimes seems somewhat random and needs to be revised. Therefore, it should be explained in more detail why and what is shown in the figures. Therefore, the results should be discussed more than just described.

    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 paper identifies the advantages of operating near certain operating points (far from the critical temperature of S-CO2) as a practical implication. Further conclusions would be desirable.

    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 writing and grammar should be improved, sometimes the sentence structure is confusing.
    It might be advantageous for the readability to place the sources at the end of the sentences so as not to interrupt the statements.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: 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. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: No, I would not like my name to appear with my report on Publons

    Reviewer: 2

    Comments:
    - The language of the manuscript needs to be revised carefully.
    - There is a recent review article of the use of surface texturing in mechanical components including seals and their leakage. This article should be included in the introduction and bears an excellent base to further discuss your results. You may want to refer to Surface texturing in machine elements− a critical discussion for rolling and sliding contacts

    • if possible, the number of equations should be reduced.

    • The group around Profito has recently published a review article on numerical approaches in surface texturing. This article may help to largely reduce the number of equations.

    • There is no discussion in the entire manuscript. Not even one citation can be found in the part results and discussion.

    • The figures are rather blurred and of poor quality.

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

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Please see my 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 my 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 my 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 my 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. All peer review content displayed here will be covered by a Creative Commons CC BY 4.0 license.: No, I would not like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/05/24

    The manuscript is about the numerical analysis of thermohydrodynamic characterisitcs of CO2 spiral groove face seals. The modelling and the results could be of interest to the research community given the complexity of the subject matter of the investigation.
    I therefore recommend acceptance if the mentioned ciritcs regarding the qualitiy communication and the presentation of results are addressed.

    Reviewed by
    Cite this review
All peer review content displayed here is covered by a Creative Commons CC BY 4.0 license.