Research on the Internal Flow Characteristics of Single- and Coaxial-Nozzle Ejectors for Hydrogen Recirculation in PEMFC
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for your paper, here the different comments:
Line 60: 'The performance of the ejector significantly depends on the
output conditions and its internal structure' example and references are needed.
Line 62-64: add references.
Line65-85: Each reference is stated without any take out message and clear conclusion with quantitative performances. More details should be stated for each study. In other hand, the number of the reference could be reduced in the introduction.
Line 98-111: move those paragraphs to the next session.
Line 111: the end of the introduction need more specification and clarification about the originality of this work and literature gap.
Line140: mp already defined in the introduction.
Line143: Typo.
Line148-149: the order of figure 3 components are stated wrongly.
Specify for the single nozzle, where the secondary flow is introduced?
Line156: Based on what this reference has been selected, elaborate more in details and related to the entrainment ratio and performances.
Line 167: specify the reason with references of the selected turbulence model.
Line 167: in order to capture the boundary layer, a wall treatment isn't used and y+ less than one is selected. Please correct the statement.
Line 195: specify the number of cells, refinement ratio and more details about the mesh for the three level of mesh.
figure4: the mesh lines are difficult to see, change the color
Figure5: How could you conclude that the medium mesh is the best choice? there is no convergence trend or an experimental reference to compare to it. The idea of comparing in figure 6 is valid however, any guarantee that the refined mesh could improve the results. Explain
Line 226: specify how you calculated the sound speed and its value.
Line247: any reason to conclude that it's caused by vortices? any support for this statement
Figure 8: the colormap bounding is different for each case, the comparison is impossible and all the corresponding statement should be rechecked
Author Response
Dear editor and reviewer
(Journal of Applied Sciences)
The authors would like to deeply thank the editor and reviewer for reviewing the paper and providing constructive remarks.
We have revised the manuscript based on the reviewer’s and the editor’s comments. It has greatly helped us to improve our work.
Detailed answers to the review comments were provided in this document. The corresponding modifications in the manuscript are described at each answer, and also highlighted with blue color in the revised manuscript. Big modifications including corrections of English are also progressed in the revised manuscript.
So, please check the highlighted parts of the revised manuscript.
Sincerely yours,
Prof. Jinwook Lee
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsHere are 5 minor revision suggestions for the manuscript:
1. **Clarify Abstract-Results Alignment**
> *Issue:* The abstract states higher diameter ratios (Dr) cause "diminished performance at low power outputs," but Table 7 shows Dr=3.05/3.55 outperform the single-nozzle ejector at ≥5 bar (medium-high load). The exception is Dr=3.55 at 4 bar (Φ=0.446).
> *Suggestion:* Specify "very low power outputs" (e.g., ≤4 bar) in the abstract to align with data, or note that performance loss only occurs for *specific* high-Dr designs under ultra-low loads.
2. **Justify Turbulence Model Selection**
> *Issue:* Section 2.1.2 states the RNG k–ε model was used but lacks justification for choosing it over alternatives (e.g., SST k–ω in [12] or LES in [16]), especially given observed shocks/pulsations.
> *Suggestion:* Briefly cite validation against [11]’s experiments or computational efficiency as rationale, or reference literature supporting RNG k–ε for supersonic ejector flows.
3. **Improve Figure Readability**
> *Issue:*
> - Fig. 3 labels (e.g., \(D_{m1}\), \(D_{m2}\)) are too small.
> - Fig. 8 velocity subfigures lack uniform color scales, hindering cross-comparison.
> *Suggestion:*
> - Enlarge annotations in Fig. 3 or add zoomed insets.
> - Standardize the velocity color bar range across all Fig. 8 subplots and specify units in the caption.
4. **Define Acronyms/Abbreviations at First Use**
> *Issue:* "PEMFC" appears in the abstract without definition. "Dr" (diameter ratio) is introduced in Section 3 without referencing Eq. (2).
> *Suggestion:*
> - Revise the abstract’s opening to: "Hydrogen proton exchange membrane fuel cells (PEMFCs)...".
> - Introduce "Dr" in Section 3 as: "diameter ratio \(D_r\) (Eq. 2)".
5. **Complete Missing Data in Table 3**
> *Issue:* Table 3 omits units for nozzle throat diameter (\(D_n\)) and leaves \(D_c\) values blank for Dr=1.55/2.05/3.05/3.55 (only Dr=2.55 is filled).
> *Suggestion:*
> - Add "(mm)" to the "Nozzle Throat Diameter (\(D_n\))" header.
> - Populate \(D_c\) values using \(D_r = D_c / D_n\) (e.g., for Dr=1.55: \(D_c = 1.55 \times 2.04 = 3.16\) mm).
Author Response
Dear editor and reviewer
(Journal of Applied Sciences)
The authors would like to deeply thank the editor and reviewer for reviewing the paper and providing constructive remarks.
We have revised the manuscript based on the reviewer’s and the editor’s comments. It has greatly helped us to improve our work.
Detailed answers to the review comments were provided in this document. The corresponding modifications in the manuscript are described at each answer, and also highlighted with blue color in the revised manuscript. Big modifications including corrections of English are also progressed in the revised manuscript.
So, please check the highlighted parts of the revised manuscript.
Sincerely yours,
Prof. Jinwook Lee
Author Response File: Author Response.pdf
