Assessment of Sensitivity to Evaluate the Impact of Operating Parameters on Stability and Performance in Proton Exchange Membrane Fuel Cells
Round 1
Reviewer 1 Report
The authors present a Monte Carlo sensitivity analysis of PEMFC performance with respect to various operating conditions, using a physicochemical model. The work seems to be sound but some aspects of presentation require improvement prior to publication. This will better contextualise the work and ensure that the key conclusions are made apparent.
1. The authors should ensure to cite and identify novelty with respect to the conceptually similar work of Jin et al. (2021) Energy Conversion and Management 228, 113727.
2. It is not made clear how all the calibration parameters listed in Table 4 enter into the model. The dependence of boundary conditions or material properties upon these parameters should be made clearer. In particular, I could not understand how cell temperature, Tcell, can be varied independently from the inlet temperatures of Tan and Tcat. If this represents an environmental temperature with which heat is exchanged in the thermal part of the model, the boundary condition should be stated explicitly.
2. Excessive detail is given for operating variables with very low sensitivity. I think that Figs. 8-10 are unnecessary as they analyse only extremely small variations. In discussing Fig. 11 the authors should emphasise the significantly different vertical scales between the two subfigures. This also applies to the comparison of Figs. 5/6 with Figs. 3/4.
3. In Fig. 3a and the comparable polarisation curves thereafter, I did not understand the locations of the points on the graphs. Why are these absent and represented as subfigures specifically at the current densities at which the model was solved (as apparently indicated by ovals)? I found the subfigures confusing and a direct representation of the data would be preferred.
Besides these overall issues, a list of typographical/presentation errors follows which the authors should follow. An English-language review overall would aid comprehensibility.
- Lines 87, 454-455: Missing superscripts from units "A/cm2".
- Line 124: Reference [32] is "Dickinson et al.", not "Edmund et al."
- Lines 213-214: The words "pressure of" are differently formatted.
- Table 5: Please use symbolic notation rather than verbal description for the the listed parameters, so that they can be compared directly to the listed equations. List all boundary conditions as equations where not already present.
- Table 5 and elsewhere: In print rather than code, please use scientific notation such as "2.25 × 10-5". Writing "2.25e-5" is meaningful in a specific software language but has no unambiguous meaning in scientific text.
- Table 5: The SI units "kmol" and "kg" should not be capitalised.
- Line 300: Figure 3 is referred to as Figure 5.
- In Fig. 3b and similar figures, indicate which y-axis scale (left or right) corresponds to which graph (bar chart or line graph).
- Eq. (19) seems to contain a mistake, as the index n which is summed over in the first part does not index any of the quantities in the sum, and the quantity K(i) is unused. Please check and correct.
Author Response
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Reviewer 2 Report
The manuscript is devoted to the influence of the operating parameters on the performance of proton exchange membranes fuel cells. Authors developed a mathematical model that allowed them to describe the influence of key parameters, such as cell operating temperature, anode/cathode operating pressures, mass flow rates and inlet temperatures.
The design of the numerical experiment is correct and the results might by significant for both scientific community and for industrial applications. However the quality of the presentation of the model and obtained results must be significantly improved before the publication.
Some of the issues that need to be addressed include:
- The list of parameters that are analysed should be included in the abstract.
- All of the parameters used in section 2 must be adequately described in the text after their first use (not only in the list at the end of the article). This includes the parameters in all the equations and tables, as well as the abbreviations used in the text.
- The sentence in lines 139-140 and eq. 6,7 are redundant (they repeat the information from lines 128-130
- Section 2.5 (boundary conditions) should be placed before section 2.4 (meshing).
- What does "grid number" mean? Is it "the number of discrete grid points/elements"? If yes why only two numbers for each grid are given if the model is three-dimensional?
- Who is the producer of the UG software used for modelling? Is this software freeware or commercial? These should be explicitly stated.
- In section 3.1: What is the difference between "calculated results" and "simulated results". Shouldn't it be "results obtained using this model" and results obtained by "results obtained by Mohammedi et al."?
- What are the key differences between this model and model presented in reference 9. This should be clearly stated.
- In lines 263-266, the difference between experimental performance and results of the model is mentioned with no actual comparison given.
- The abbreviations used in table 4 should be defined either in the table caption or in the text before the table.
- In table 5 two different values of "anode reference current density" are given. Same for "anode/cathode exchange coefficient". Please check it.
- In line 300: "Fig. 5 depicts", should be "Fig. 3 depicts".
- In line 365: "obtained by COP", should be "obtained by AOP".
- In Figures 7 and 12-14: Units are missing in the legend.
- Axes descriptions in Figure 11 are hard to read, please reformat.
- Extensive language editing is required, as numerous sentences throughout the text are not clear.
Author Response
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Reviewer 3 Report
The manuscript tries to describe the application of local sensitivity analysis (LSA) to analyze the sensitivity analysis of proton exchange membrane fuel cell (PEMFC) parameters. The title and abstract are appropriate for the content of the text. However, the background/literature review on this topic is not sufficient.
Strengths: The authors used a method that requires less simulation.
Weakness:
- The authors failed to include error bars in Figures 1b, 2, 3, 4, 5, 6, 8, 9, 10, and 11 data points.
- The manuscript is not comprehensive enough due to limited references – the manuscript could be improved if recent research findings (such as International Journal of Hydrogen Energy35 (2021): 18589-18603, Fuel285 (2021): 119194, and International Journal of Energy Research 45.2 (2021): 1227-1245, etc.) are included.
Author Response
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Round 2
Reviewer 1 Report
The authors have responded to all criticisms raised by the various reviewers. I am satisfied that the article is now publishable.
One typographical error can be corrected before publication (no further review required):
- In Table 5, "Ionic conductivity" has been misspelt "Inoic conductivity", and the symbol should be σmem, not σs.
Moderate language review by MDPI is required to aid comprehension. I note that the authors mention in their response to one of the other reviewers that they had already received language editing from Elsevier - if so, they should get their money back, since the the abstract and the 1st paragraph of the introduction alone contain several clear errors in English language grammar, usage and style. The standard English language at present is sufficient to understand the scientific work undertaken, but the paper would be much easier to follow if further revisions were made.
Author Response
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Reviewer 2 Report
This is the second review of the manuscript devoted to the influence of the operating parameters on the performance of proton exchange membranes fuel cells. As mentioned in the previous review, the design of the numerical experiment is correct and the results might by significant for both scientific community and for industrial applications.
In corrected version authors have addressed the issues mentioned by the reviewer in satisfactory matter, significantly improving the quality of the presentation of the model and obtained results.
The following issues still require corrections:
1.
The issue with “grid number” remains. The comment in the previous review did not concern the table 3 (which was clear already in the previous version.)
It concerned the sentence “Four sets of regular hexahedral structural grids were prepared with grid numbers 100,468, 128,600, 140,400, 158,400 to validate the grid independence.”
What is the meaning of the pair “140,400”. Is it the same in pair “distance/number of elements” as in table 3? If yes, then for which domain and in which direction (X, Y or Z)? Why would you change the distance to test for different grids?
Or is it not a pair but a value “140400” representing "the total number of grid elements in all domains"? But if the total number of elements selected for calculations was 140400, then why the total number of grid elements in all domains calculated from table 3 is:
2*(30*100*20+10*100*100+30*100*15+30*100*5)+30*100*15 = 485000
Note that “grid” by definition is “a network of lines that cross each other“ or “a network of grid elements”. Hence instead of “grid number” you should use in the text “the number of grid elements”.
2.
The sentence “A 3D model design software known as UG (Unigraphics NX) was used in this study, which developed by Siemens, and ...” suggests that this study was developed by Siemens. Please change to: “A 3D model design software known as UG (Unigraphics NX, developed by Siemens) was used in this study, and ...”
3.
Mohammedi is not the only author in ref. 9 therefore “… results obtained by Mohammedi, … “ should be “… results obtained by Mohammedi et al., … “
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