Multiphysics Co-Simulation and Experimental Study of Deep-Sea Hydrothermal Energy Generation System
Round 1
Reviewer 1 Report
The authors present both numerical and experimental studies for a deep-sea hydrothermal energy harvesting system. The numerical approach is a transient simulation, utilizing multiphysics modelling, i.e. consisting of CFD and conjugate thermoelectric calculation. Their numerical approach is also verified by appropriately designed experiments. The overall research work is very interesting, of scientific soundness and contributes to the field. This reviewer proposes that the effort and the thorough work of the authors should be published, however after a (rather) minor revision.
Remarks / questions of this reviewer
1) Focus on presenting the characteristics of TEG technology (advantages-disadvantages) to justify why it is suitable for the application under consideration.
2) Concerning the solution of the heat conduction problem in a PN pair, as described in Figures 2 and 3, are the P and N arms solved separately or together. In other words, for the temperature Ti in the i-th layer is the same for both arms?
3) Figure 6 is not referred or discussed in the text.
4) Add a line in Table 1 as a third line where the temperature difference ΔΤch, i.e. Thot-Tcold will be written.
5) The expression presented as equation (22) refers to which of the curves in Figure 7? Is it a global one, i.e. it describes all the curves in Figures 6(a)-6(c)? The same question for equation (24) and Figure 8.
6) Examine including one more plot in Figure 6, in which all the 5 fitted curves (no the experiments) will be included. In this case the y-axis will be the same and the relevant position of the curves will be seen. The same for Figure 7.
7) Concerning the results presented on Figure 9, comment a little if possible on where the high discrepancy occurs, i.e. region of high ΔΤ and high pressure.
8) In page 12, line 305, the equivalent thermal conductivity of the TEG is referred. What is it? Isn’t it a distribution λ(x,y,z) in equations (5) and (6)? An averaged value is used instead in the CFD? Please clarify the issue.
9) Concerning the text in page 15, line 379, the temperatures obtained for hot and cold ends of TEG by CFD are constant? Averaged? Distribution T(x,y,z,t)? What temperatures are assigned to P and N arms in CFD? Or CFD solves for TEG as a whole? Please explain.
10) The spiral spoiler is modeled and included in the flow domain and taken into account in the CFD simulation.
11) The Use of English language in the text requires improvements.
The Use of English language in the text requires improvements.
Some modifications are proposed in what follows.
Remarks / proposed modifications concerning the language (P means Page, L means Line)
P1, L41: remove ‘also’
P2, L51-55: ‘The temperature of hydrothermal plumes is generally 60 to 350 ℃, and the highest temperature is more than 400 ℃. The heat flux of a typical single high-temperature vent can reach 10 megawatts. While the surrounding cold water is usually below 5 ℃. There is a huge temperature difference near the hydrothermal vents [13].’ à ‘The temperature of hydrothermal plumes is generally 60 to 350 ℃, and the highest temperature is more than 400 ℃, while the temperature of the surrounding cold water is usually below 5 ℃. Thus, there is a huge temperature difference near the hydrothermal vents and the heat flux of a typical single high-temperature vent can reach 10 megawatts [13].’
P2, L78-79: ’… been deeply studied. What’s more, the …’ à ‘… been thoroughly studied in depth. Furthermore, the fact that the …’
P2, L80: ‘how’ à ‘the way’
P2, L84: ‘is studied. And’ à ‘is studied and’
P2, L85: ‘between’ à ‘of’
P2, L88: Start a new paragraph with the sentence ‘The rest of this article …’
P2, L89: ‘charged’ à ‘charging’
P2, L92: ‘studied. And’ à ‘studied and’
P3, L102: ‘And the study’s conclusions’ à ‘The conclusions of this study’
P3, L110-114: ‘When there is a temperature difference between two different thermoelectric materials, due to the thermoelectric properties of the semiconductor material, the potential difference and current will be induced at both ends, and the thermoelectric effect will be caused at the same time. This phenomenon is called the thermoelectric power generation of TEG [18].’ à ‘Whenever there is a temperature difference between two different thermoelectric materials, the potential difference and current will be induced at both ends, due to the thermoelectric properties of the semiconductor material and, at the same time, the thermoelectric effect will be caused. This phenomenon is called the thermoelectric power generation of TEG [18].’
P3, L127: ‘will increase’ à ‘is increased’
P4, L136: ‘as temperature function of T’ à ‘as a function of temperature T’
P4, L138-140: ‘… conductivity of the ceramic sheet is regarded as a constant; (3) For the convenience of the method Iterative solution calculation, the default load resistance is always equal to the internal resistance of the TEG.’ à ‘… conductivity of the two corresponding ceramic sheets is regarded as constants; (3) For the convenience of the iterative calculation method, the default load resistance is always equal to the internal resistance of the TEG.’
P4, L150: ‘m nodes. And’ à ‘m temperature nodes and’
P4, L152: ‘is the origin of x. According’ à ‘is set as the origin of x axis. According’
P4, L160: ‘the Difference Method (DM)’ à ‘the Finite Difference Method (FDM)’
P5, L169: ‘a system of’ à ‘a tridiagonal system of’
P5, L182: ‘of lumped parameter model and distributed parameter model is obtained as shown in’ à ‘of the lumped and the distributed parameter models is obtained as shown in’
P5, L184: ‘It can be seen from the figure that the data’ à ‘As it becomes evident from this figure, the data’
P5, L185: ‘model is always larger than that of the’ à ‘model in all cases overestimates that of the’
P5, L187: ‘gap’ à ‘discrepancy’
P6, L191-192: ‘All of the above reasons will lead to large model errors. To further verify’ à ‘All these reasons lead to large model errors. To verify’
P6, L193: ‘are’ à ‘were’
P6, L206: ‘and the theoretical value is solved,’ à ‘and the numerically predicted value was calculated,’
P7, L209-211: ‘Under different conditions (Table 1), the relative error curves between the theoretical values of the distributed and centralized parameter TEG models and the experimentally measured values.’ à ‘Relative error curves between the numerically predicted values of the distributed and lumped parameter TEG models and the experimentally measured values, under different conditions (Table 1).’
P7, L212: ‘the theoretical values’ à ‘the numerically predicted values’
P7, L230-231: ‘The platform is mainly composed of pressure control and temperature control two parts.’ à ‘The platform is mainly composed of two control parts; one for pressure and one for temperature.’
P7, L234: ‘will be subjected’ à ‘is subjected’
P7, L236: ‘TEG. the’ à ‘TEG. The’
P7, L238-242: Re-write the sentences in a way that they will describe things, not like guidelines! Avoid using keep, increase, record etc. For example: The temperature of the TEG should be kept stable etc.
P9, L261-262: ‘As shown in Figure 8, there are the TEG internal resistance under pressure’ à ‘Figure 8 presents the TEG internal resistance under pressure’
P11, L286: ‘in the paper [17]’ à ‘in [17]’
P11, L286: ‘in the previous CFD’ à ‘in these CFD’
P11, L288: ‘only the velocity field and temperature field’ à ‘only the velocity and temperature fields’
P11, L289: ‘, and’ à ‘, while’
P11, L291: ‘simulation will’ à ‘simulation has to’
P12, L299: ‘which is used as the inlet’ à ‘which are used as inlet’
P12, L300: ‘analysis. And the’ à ‘analysis. The’
P12, L301: ‘In each calculation iteration process’ à ‘In each iteration, during the calculation process’
P12, L302: ‘will be extracted’ à ‘is extracted’
P12, L307: ‘This whole’ à ‘The whole’
P16, LL406, 413: ‘when time=300ms’ à ‘at time 300 ms’
P17, L427: ‘And when’ à ‘When’
P17, L428: ‘, The’ à ‘, the’
P17, L433: ‘It can’ à ‘As it can’
P17, L434: ‘figure that when’ à ‘figure, when’
P18, L446: ‘are carried’ à ‘were carried’
P18, L460: ‘can also be’ à ‘can be’
P18, L461: ‘In this study, the specific parameters of the test conditions’ à ‘The specific parameters of the test conditions used in this study,’
P18, L469: ‘fluids conditions’ à ‘flow conditions’
P18, L473: ‘are recorded’ à ‘were recorded’
P18, L474-475: ‘… respectively. And the average hot and cold end temperature and the temperature difference can’ à ‘… respectively, so the average hot and cold end temperature and the temperature difference could’
P19, L480: ‘the open circuit voltage and maximum output power’ à ‘the open circuit voltage (Fig. 20(b)) and maximum output power (Fig. 20(c))’
P20, L498: ‘At the same time, the condition parameters listed in Table 2 are applied’ à ‘The condition parameters listed in Table 2 were also applied’
P20, L500: ‘can be’ à ‘could be’
P20, L505: ‘and 150mm, respectively.’ à ‘and 150mm.’
P20, L507: ‘Finally, the average’ à ‘The average’
P20, L510: ‘is consistent’ à ‘are consistent’
P21, L525: ‘At this time’ à ‘At that time’
P22, L539: ‘the enhanced’ à ‘an enhanced’
P22, L550: ‘ahead. And it’ à ‘ahead. Furthermore, it’
P22, L540-544: Please, re-write this text with more simple and smaller sentences to make it clearer
Author Response
Thanks for your recognition of our manuscript, and also thank you very much for your valuable comments on our manuscript.
Please see the attachment about the response to your comments.
Kindest wishes to you, Thank you!
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this study a comprehensive multiphysics analysis of an energy generation system based on thermoelectrical generators uses hydrothermal energy on the ocean seabed is resented. The main purpose of such a technics is the long term charge the deap-sea research equipment. The study represents an improved distributed thermoelectrical model of a single thermoelectric generator, the influence of the pressure on the generator's output parameters, a comprehensive multiphysics model and experimental validation of an own designed energy generation system. The study is properly design as it is pointed out what is missing in existing studies. It is clear that it contributes to the existing knowledges in the field of deap-sea hydrothermal energy generation. In order to better understand the results I have several questions to the authors:
- Please discus at each step study in the results the geometrical size of the thermoelectric generators. We know that the generated power depends on the heat transfer area. Please add information how much energy is needed to be generated for continually operation of some deap-sea equipment. Do you expect that it could be the main power source or auxiliary unit;
- In Section 2.1, please explain how the efficiency of TEG was estimated;
- Please improve the conclusions by adding the most important numerical findings of you results.
Author Response
Thanks for your recognition of our manuscript, and also thank you very much for your valuable comments on our manuscript.
Please see the attachment about the response to your comments.
Kindest wishes to you, Thank you!
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper considers a deep-sea hydrothermal energy generation system.
The problem and background are well set out. The authors consider a number of different aspects using a range of simulation and experimental methods. This rage added to the description of the operation of the energy generator, but means that each part is only described and discussed briefly and this can lead to it being hard to follow the details of what was done.
I feel this is an interesting paper and is suitable for publication, but I would ask that the authors consider the following points first.
· In equations (22) and (23) why is the expression in equation (22) a cubic and equation (24) raised to the firth power? The data in figures 7 and 8 do not particularly show this behaviour.
· It would be beneficial to give more details of the different simulation approached. For example in the fluent model in Figure 13 and the associated discussion, it is not possible to evaluate features such as the extend of the domain, the boundary conditions, the physics models applied (e.g is it turbulent, compressible, etc. ), the mesh quality, etc.
· In figure 23, the measured power and voltage is approximately constant while the are clear variations in the modelled data. Could the authors elaborate on this?
· The paper is focussed on using this technology to power deep-water experimentation and monitoring. It would be interesting if the authors could also consider whither the approach would be applicable more generally for generating renewable energy for general use.
Author Response
Thanks for your recognition of our manuscript, and also thank you very much for your valuable comments on our manuscript.
Please see the attachment about the response to your comments.
Kindest wishes to you, Thank you!
Author Response File: Author Response.pdf
Reviewer 4 Report
The paper thematically fits into the area of interest of the journal. Undoubtedly, the strength of the manuscript is the link between numerical analysis and experiment. Errors of an editorial and factual nature were detected in the work, which should be eliminated before publication. I have included a list of my most important comments and concerns that should be addressed by the authors below.
1. The "Abstract" section should be short and include the thesis and research hypotheses. This section should also include the most important qualitative and quantitative research results obtained by the authors. Please improve it.
2 The "Introduction" section should include both qualitative and quantitative literature results. This will allow uninitiated readers to visualize the issue.
3) I recommend creating a "Nomenclature" section, which should include all symbols and abbreviations used in the manuscript. If possible, please provide SI units to the symbols defined.
4. In the summary of the "Introduction" section, highlight the novelty and originality of the work and indicate what literature fills the manuscript presented by the authors. Please correct this.
5. In Chapter 2, in lines 105 to 114, there is publicly available information and does not contribute anything new to the state of knowledge. Hence, please remove them.
6. Poor quality (sharpness) of figure 3. Please improve it.
7. Chapter 2 lacks technical information on the test object (TEG). Specify the type, manufacturer and basic operating parameters, i.e. operating temperatures, power, etc. (proposes to make such a summary in a table). Please complete this.
8. Chapter 2 lacks complete boundary conditions for which numerical calculations were made. Please supplement this.
9. Were the calculations shown in Figure 4 performed for a single TEG element? Please include such information in the manuscript.
10. The factual description of the simulation results shown in Figure 4 is insufficient. An analysis of the obtained results in relation to literature data should be included. Please complete it.
11. No information on the TEG measurement system and a diagram with measurement points and measured quantities. Provide data on the test apparatus (i.e., manufacturer, model or type of device, measuring range, measurement error, etc.).
12. How the TEG was loaded. Please comment and include relevant information in the manuscript.
13. No description of measurement methods, which will make it difficult for other researchers to reproduce the experiment and thus verify and validate the authors' findings. Please supplement this.
14. The font size in Figure 7 is too small and invisible. The type and size of the font in the figures should be the same and the text of the manuscript. Please correct this and the remark should be applied throughout the manuscript.
15. The factual description of the results shown in Figures 7 and 9 is insufficient. One sentence description is not enough. Please make an analysis of the results. Please complete it.
16. In Figure 11, include the characteristic dimensions of the device (i.e., height, diameter, spacing between Peltier modules, etc.). Please complete this.
17. In Figure 15, add the axes (x and y) and characteristic dimensions (scale). Please complete this.
18. Poor quality (sharpness) of Figure 16. Please correct this and revise the manuscript in this regard.
19. In the manuscript, the authors use two temperature scales (degrees Celsius and Kelvin scale). The notation should be uniform throughout the manuscript. Please take one scale and use it consistently throughout the manuscript.
20. In Figure 18, mark references to the research apparatus, the description of which should be included below the figure.
21. In the "Concluison" section, the most important qualitative and quantitative results of the authors' research should be included on the basis of which general conclusions should be drawn. Please improve it.
Author Response
Thanks for your recognition of our manuscript, and also thank you very much for your valuable comments on our manuscript.
Please see the attachment about the response to your comments.
Kindest wishes to you, Thank you!
Author Response File: Author Response.pdf
Round 2
Reviewer 4 Report
The authors addressed my comments and, in my opinion, made the necessary corrections to the manuscript. I recommend this manuscript for publication.
