Enhancing Heat Removal and H2O Retention in Passive Air-Cooled Polymer Electrolyte Membrane Fuel Cells by Altering Flow Field Geometry
Round 1
Reviewer 1 Report
Comments and Suggestions for Authorsattached
Comments for author File: 
Comments.pdf
Author Response
Reviewer: 1 (modifications related to reviewer 1 comments have been highlighted in green)
- The quality and significance of the research. The detailed suggestions by the reviewer are the followings.
- Page 11 line 188: 5th design → 3rd design
Authors Response: The text has been checked and revised in sections 2.4 and 2.5
- Page 13 line 221: Design 3 → Design 5.
Authors Response: The text has been checked and revised in sections 2.6 and 2.7
- The calculation of moisture content and the influence of channel inlet air humidity on moisture concentration are not explained.
Authors Response: the main scope of the current study was to investigate shape of the cathode flow field channel on the water content, heat removal, and current density. The influence of air humidity at the inlet is not taken into consideration.
- In the channel volumetric flow rate of air is changed due to the reaction of oxygen and hydrogen to form water is not considered. If air is supply in excess, please specify the excess amount to verify the assumption that the molar flow rate change due to reaction can be negligible.
Authors Response: The inlet air velocity is set to constant value of 2.7 m/s based on Lim et al. [24] assumption.
- The detail correlation between water content in the channel and pressure change in the channel is not explained.
Authors Response: the pressure change was not included in the analyses, as the main focus was on the water retention, current density, and temperature.
- The clarity of the presentation. Please rewrite your conclusion. The manuscript could provide more information to the reader if the authors provided design guidelines to create a better design that provides better heat removal and better moisture retention without flooding.
Authors Response: Comprehensive revision of the conclusion section has been carried out to provide clearer and better insight on the outcomes of the present study.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe article only uses CFD to do a simple analysis, and the depth and innovation of the research are insufficient.
Comments on the Quality of English LanguageThe Quality of English Language needs to be further improved.
Author Response
Reviewer: 2
The article only uses CFD to do a simple analysis, and the depth and innovation of the research are insufficient.
Authors Response: CFD is crucial for analyzing PEM fuel cells due to its ability to simulate fluid flow within the cell. The present study focuses on the geometry of the cathode flow field and its impact on the performance of the cell. Novel designs of cathode side flow channels and their impact on crucial parameters such as heat removal, water retention, and current flux density within the PEM fuel cell were investigated in this paper. Although the modifications to the cathode flow field resulted in only minor improvements, the obtained data can help to set the path to the ongoing advancements in fuel cell technology. Ultimately, CFD validates experimental data and provides insights for design improvement, making it indispensable for understanding and optimizing PEM fuel cell performance.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe MS investigates 5 different 3D flow field designs for the passive air-cooled PEM fuel cell to enhance heat removal and H2O retention. This is a completely numerical study without any empirical verification. Since the problems of heat and water management are of great interest for the FC technology, the MS is a relevant work, but it requires serious improvement before publication.
1. The authors don't provide the general equations underlying the studied physical processes and electrochemical reactions. However this is crucial to justify the significance and scientific sound of the work. Please provide proper analysis when describing your model. H2O is not produced after the electrolysis (line 121), but through the oxygen reduction reaction at the cathode.
2. The MS contains many similar or even identical figures (as the fig. 5 and 6). The authors should reduce the number of figures or transfer them to the Supplementary.
3. Some of the flow field designs are depicted as unrealistic. What about mechanical strength of the flow fields depicted in the figures 8 and 9?
4. The simulation results show that channel design type has only a minor impact on FC performance (table 5). The authors should discuss that in more detail to prove the significance of their research.
5. Please fix systematical misprints, such as spelling the formula of water as "h2O" and incorrect writing of indexes. Correct heading of the table 5.
Author Response
Reviewer: 3 (modifications related to reviewer 3 comments are highlighted in Turquoise)
- The authors don't provide the general equations underlying the studied physical processes and electrochemical reactions. However, this is crucial to justify the significance and scientific sound of the work. Please provide proper analysis when describing your model. H2O is not produced after the electrolysis (line 121), but through the oxygen reduction reaction at the cathode.
Authors Response: In order to reduce the length of the manuscript, the general and governing equations are not included. However, the reader can refer to reference [30] as highlighted in Section 2.8 for more details on the equations used to govern the different parts of the fuel cell.
- The MS contains many similar or even identical figures (as the fig. 5 and 6). The authors should reduce the number of figures or transfer them to the Supplementary.
Authors Response: All unnecessary figure has been removed (Figure 1, Figure 3, Figure 10, Table 3, Table 4, Figure 13, Figure 14)
- Some of the flow field designs are depicted as unrealistic. What about mechanical strength of the flow fields depicted in the figures 8 and 9?
Authors Response: The channels in Figures 8 and 9 are the cathode side channel and it is enclosed in the casing of a PEM fuel cell, thus the thin wall does not affect the mechanical integrity of the cell.
- The simulation results show that channel design type has only a minor impact on FC performance (table 5). The authors should discuss that in more detail to prove the significance of their research.
Authors Response: More discission have been included in the conclusion section to highlight the significance although very small changes obtained in heat removal.
- Please fix systematical misprints, such as spelling the formula of water as "h2O" and incorrect writing of indexes. Correct heading of the table 5.
Authors Response: Comprehensive editing and language proofreading was carried out on the manuscript to eliminate any misprints and grammatical errors.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe manuscript has a similar idea, figures, and text with the REF. https://doi.org/10.1016/j.ijhydene.2019.07.128, without own novelty; many sentences are rephrased or rewrote. Please, check it by yourself. My opinion - reject
Comments:
1. The Introduction section should be more focused on areas directly related to the topic of the work. The list of references should be expanded.
2. Please, indicate the novelty of the research in comparison with previously published data, highlight the main results of the work. The use of PEM fuel cells in UAVs does not seem original enough.
3. It is required to correlate the presented flow-field geometry with previously published ones, and justify your choice based on the results.
4. The manuscript also needs some organization; it is overloaded with parts and figures that require systematization. Manuscript looks like a part of a report.
5. The manuscript looks like a draft, words and terms are missing, there are many errors. English editing is required. Authors should carefully rewrite and update the manuscript for improve its quality.
Author Response
Reviewer: 4 (modifications related to reviewer 4 comments are highlighted in yellow)
- The manuscript has a similar idea, figures, and text with the REF. https://doi.org/10.1016/j.ijhydene.2019.07.128, without own novelty; many sentences are rephrased or rewrote.
Authors Response: The main concept of our study and the one published by Lee et al. mentioned above is the same, which is improving the water retention and heat removal. However, in our study we suggested five novel cathode flow field designs namely: Converging, Diverging, Conventional with cylindrical fins, Trapezium, and Semi Circular). In Le et al. study, one design (diverging cathode flow field) was discussed.
- The Introduction section should be more focused on areas directly related to the topic of the work. The list of references should be expanded.
Authors Response: The introduction section has been rewritten to ensure that it focuses directly on the topic of interest in the present study. The list of references has been expanded as well.
- Please, indicate the novelty of the research in comparison with previously published data, highlight the main results of the work. The use of PEM fuel cells in UAVs does not seem original enough.
Authors Response: The novelty of the current study in comparison to the available literature is highlighted in the last paragraph in the Introduction section.
- It is required to correlate the presented flow-field geometry with previously published ones, and justify your choice based on the results.
Authors Response: The data from Design 2 (converging channel) was compared and justified to previously published study in reference [31] in page 20.
- The manuscript also needs some organization; it is overloaded with parts and figures that require systematization. Manuscript looks like a part of a report.
Authors Response: Comprehensive review was carried out on the manuscript to improve the organization of the data and figures.
- The manuscript looks like a draft, words and terms are missing, there are many errors. English editing is required. Authors should carefully rewrite and update the manuscript for improve its quality.
Authors Response: Comprehensive editing and language proofreading was carried out on the manuscript to eliminate any misprints and grammatical errors.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe author responded to questions about the paper. The quality of figures should be improved. The discussion of the results needs further strengthening.
Comments on the Quality of English LanguageMinor editing of English language required.
Author Response
Response to Reviewer 2 comments (modifications related to reviewer 2 comments are highlighted in yellow in the revised manuscript):
- The quality of figures should be improved.
Response: The quality and resolution of all Figures have been improved in the revised manuscript.
- The discussion of the results needs further strengthening.
Response: Further improvement on the discussion of results was implemented as highlighted in yellow in page 17 and page 20 of the revised manuscript.
- Minor editing of English language required.
Response: Comprehensive editing and language proofreading was carried out on the manuscript using the English language editing by MDPI to eliminate any language errors.
Reviewer 3 Report
Comments and Suggestions for Authors The authors have done a lot to improve the manuscript.Now it can be recommended for publication.
Author Response
Reviewer 3 comment
The authors have done a lot to improve the manuscript. Now it can be recommended for publication.
Response: No response is required.
Reviewer 4 Report
Comments and Suggestions for AuthorsBy previouse Review:
The reviewer find out of the intentional plagiarism in the manuscript (vs the work https://doi.org/10.1016/j.ijhydene.2019.07.128 Innovative cathode flow-field design for passive air-cooled polymer electrolyte membrane (PEM) fuel cell stacks) without reference.
Example:
Figure (1) manuscript = Figure 1 https://doi.org/10.1016/j.ijhydene.2019.07.128
The description from manuscript:
2. Description of the new design and the principle of work
Line 58-67
The air-cooled PEM fuel cell system is classed as active, or passive based on the air supply mechanism. The reactant air for the coolant air and oxygen reduction (ORR) are supplied separately in the structure of an active type of air-cooled PEM fuel cell. In other words, there are two distinct flow routes for each air that can be optimized for optimal fuel cell functioning. The structure of the passive air-cooled polymer is dependent on cooling via natural air transmission against the surface area of the fuel cell stack. Passive cooling has also an option of free or forced convection of the reactant or product. Hence, in other words, passive air-cooled PEM fuel cell has a way simpler design than that of the active type. Therefore, since passive air-cooled PEM fuel cell is relatively small in size, easier system and has light property compared to active cooling, passive air-cooled PEM fuel cell is preferred. However, the risk of dehydration due to the excessive dry air is higher in this case.
Is very similar to REF. https://doi.org/10.1016/j.ijhydene.2019.07.128:
Air-cooled PEM fuel cell systems can be classified as active type and passive type, depending on the air supply method. In an active-type air-cooled PEM fuel cell system, the reactant air for the oxygen reduction reaction (ORR) and the coolant air are separately supplied through two different flow paths and thus can be properly controlled for optimal fuel cell operation. By contrast, passive air-cooled PEM fuel cell systems rely on cooling via natural convection of air against the external surface area of the fuel cell stack. Cooling via free or forced convection of the reactant or product also falls under the category of passive cooling. Therefore, in terms of system configuration, a passive-type air-cooled PEM fuel cell system is simpler than an active-type system and is thus better suited to small-scale UAV and drone applications that require a lightweight fuel cell stack and system.
Line 24-26 manuscript
A cooling channel design geometry is not the only method of enhancing heat removal and H2O retention. A study done by Lasbet et al. [16], clarify that the channel geometry during conviction does not only concern the surface area involved but the trajectory of the streamlines is also considered.
Is very similar to REF. https://doi.org/10.1016/j.ijhydene.2019.07.128:
Channel design not only concerns the surface area involved in convection but also considers the trajectory of stream lines, as studied by Lasbet et al. [2].
You deleted the plagiarism from the manuscript.
Author Response
Response: The authors would like to clarify that no intentional plagiarism was carried out. As for Figure 1 in the original submission, citation was included in the original draft and the figure has been removed in revision 1 since the authors could not obtain a written permission from the copyright owner to include the figure in the current manuscript. Thus, it has been removed as it does not affect the coherence of the text.
