Laboratory Characterization of a Liquid Metal MHD Generator for Ocean Wave Energy Conversion

Round 1

Reviewer 1 Report

This study attempts to presented the characterization of an alternate LMMHD generator at laboratory scale that is intended to be coupled with a WEC. This paper shows that the output current and voltage were measured for different operation conditions while an estimation of the electric power and efficiency was performed from experimental measurements in laboratory environment. The topic is interesting, authors present good scientific background, the methodology is suitable and results are interesting for the readers.

I have some suggestions-corrections for this paper to be more suitable for this journal as follows:

First, the existing studies cited in the first section are not discussed in the fourth section. The authors compared research results with another four papers. I suggest that the authors should summarize the research gaps on literature review in the first section and highlight the research contributions compared the existing studies (discussions are also required).

Second, some relevant studies are suggested to be sited in this paper for reviewing literature and discussing the research findings as follows:

(1)    Anwar B., M. Ferdows, M. E. Karim, M. M. Hasan, T. A. Bég, M. D. Shamshuddin, and A. Kadir (2020). Computation of Non-isothermal Thermo-convective Micropolar Fluid Dynamics in a Hall MHD Generator System with Non-linear Distending Wall. International Journal of Applied and Computational Mathematics, 6(2): 42.

(2)    Shah Z, Kumam P, Dawar A, Alzahrani EO and Thounthong P (2019). Study of the Couple Stress Convective Micropolar Fluid Flow in a Hall MHD Generator System. Front. Phys. 7:171.

(3)    Tsai, C.-C., Y.-T. Lin, J.-Y. Chang, and T.-W. Hsu (2016). A coupled-mode study on weakly viscous Bragg scattering of surface gravity waves. Ocean Engineering, 122, 136-144. 

(4)    Ellahi R, Sait SM, Shehzad N, Mobin N. Numerical simulation and mathematical modeling of electro-osmotic couette–poiseuille flow of MHD power-law nanofluid with entropy generation. Symmetry. (2019) 11:1038.

Third, in the last section, I suggest that it would be clear to have a table or map with different results compared between the experimental device of this paper and other existing prototype to highlight the advantage of the prototype design in this study. 

Author Response

We very much appreciate the careful reading of our paper by the reviewer as well as his/her suggestions to improve the work. We are glad to know that the reviewer considers that the topic of our paper is interesting with a good scientific background, suitable methodology and interesting results for the readers. We have made a very careful revision of the comments of reviewer which helped us to enrich the manuscript. In what follows, we provide a detailed response to the reviewer’s observations, indicating the modifications introduced in the manuscript. In the new version of the paper, all changes and additions are highlighted in red.

Reviewer:

-First, the existing studies cited in the first section are not discussed in the fourth section. The authors compared results with another four papers. I suggest that the authors should summarize the research gaps in the literature review in the first section and highlight the research contributions compared existing studies (discussion are also required).

Response: As recommended by the Reviewer, an extensive literature review was added in the introduction section. Several updated references were incorporated, including many relevant papers related with MHD generation and wave energy systems. The general perspective of MHD generation for wave energy applications is now broadly discussed and the particularities of our study are clarified. In the last section, we contrasted our contributions with other studies and offer suggestions for future projects (see last point below).

Reviewer:

-Second, some relevant studies are suggested to be sited in this paper for reviewing literature and discussing for research findings as follows.

Response: We have carefully revised the references suggested by the reviewer and found that they are not closely related to the topic of our paper, in particular, MHD Hall generators are a different concept that is not suitable for wave energy conversion. However, we performed a deep search of relevant updated references that were incorporated into the paper and discussed at length.

Reviewer:

-Third, in the last section I suggest that it would be clear to have a table or map with different results compared with the experimental device of this paper and other existing prototype to highlight the advantage of the prototype design of this study.

Response: As suggested by the Reviewer, we have clarified the last section by highlighting the particularities and contributions of our study, contrasting our development with other projects, particularly those carried out at the Institute of Electrical Engineering of the Chinese Academy of Sciences. As explained in the manuscript, our prototype was designed to allow a detailed measurement of the oscillatory velocity of the liquid metal inside the generator and to acquire reliable data of the output voltage and current for characterizing the performance of our device which is intended for small-scale applications, for instance, providing an energy source for oceanographic instrumentation. Further, our MHD generator uses the liquid metal galinstan, a working fluid that has not been tested before for this application. Due to the differences in scale and purpose of the Chinese prototypes and ours, we considered that it is clearer to explain the distinctions in detail instead of presenting a comparison table. We also included recommendations for future studies in the new version of the paper, particularly those that were implemented in the new design (under construction) that will be reported in a future contribution where the LMMHD generator is coupled to a WEC.

 

Reviewer 2 Report

The manuscript subject is interesting. However, the results and analysis are not very clear. More specific comments are as follows:

 

1- The introduction is quite negligible, with mostly old references (> 70% are older than 2015). Expanding the idea and explaining the problem in-depth would show the novelty of the manuscript.

 

2- The parts from other papers need to be well referenced, such as Figure 1, which is a copy from “Analysis of the oscillatory liquid metal flow in an alternate MHD generator, DOI: https://doi.org/10.31349/RevMexFis.65.239”.

3- The structure of the manuscript needs improvement. A methodology section needs to be added. Some parts, such as lines 218 to 227, belong to the introduction, not the end of the discussion.

4-The conclusion is not clear and needs to be improved. Which parts are from the literature review analysis, and which parts from the experimental analysis?

5-It is better to add also a recommendation for future studies.

Author Response

We very much appreciate the careful reading of our paper by the Reviewer as well as his/her suggestions to improve the work. We are glad to know that the Reviewer considers that the subject of our paper is interesting. We have made a very careful revision of the comments of Reviewer which helped us to enrich the manuscript. In what follows, we provide a detailed response to the Reviewer’s observations, indicating the modifications introduced in the manuscript. In the new version of the paper, all changes and additions are highlighted in red.

 

Reviewer

1. The introduction is quite negligible with mostly old references (>70% are older than 2015). Expanding the idea and explaining the problem in depth would show the novelty of the manuscript.

Response: We agree with the Reviewer that the introduction must be improved. We performed a deep literature search and updated the references, including several relevant papers related with MHD generation and wave energy systems so that the introduction was substantially rewritten. The general perspective of MHD generation for wave energy applications is now broadly discussed and the particularities of our study are clarified.

Reviewer

2. The parts from other papers need to be well referenced as Figure 1 which is a copy of the “Analysis of the oscillatory liquid metal flow in an alternate MHD generator”. DOI https://doi.org.1031349/RevMexFis65.239”

Response. We agree with the observation of the Reviewer. A new figure 1 was elaborated to substitute the previous one.

Reviewer

3. The structure of the manuscript needs improvement. A methodology section needs to be added. Some parts, such as lines 218 to 227, belong to the introduction not to the end of the discussion.

Response: As suggested by the reviewer, the second section was enlarged to include the methodology where the general procedure for the design of the prototype and the experimental performance is explained. Some methodological aspects are also discussed in sections 3 and 4. As for the paragraph mentioned by the reviewer (lines 218 to 227) we do not agree that it should be placed in the introduction since in this paragraph we compare the results of a previous analytical simplified model of the alternate MHD generator with the results obtained in the experimental campaign. 

Reviewer

4. The conclusion is not clear and needs to be improved. Which parts are from the literature review analysis and which parts from the experimental analysis?

Response: As suggested by the Reviewer, we have clarified the conclusion by highlighting the particularities and contributions of our study, contrasting our development with other projects, particularly those carried out at the Institute of Electrical Engineering of the Chinese Academy of Sciences. As explained in the manuscript, our prototype was designed to allow a detailed measurement of the oscillatory velocity of the liquid metal inside the generator and to acquire reliable data of the output voltage and current for characterizing the performance of our small-scale device.

Reviewer

5. It is better to add also a recommendation for future studies.

Response: As suggested by the Reviewer, recommendations for future studies are mentioned in the new version of the paper, particularly those that were implemented in the new design (under construction) that will be reported in a future contribution where the LMMHD generator is coupled to a WEC.

 

Round 2

Reviewer 2 Report

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