Solar Salt above 600 °C: Impact of Experimental Design on Thermodynamic Stability Results
Round 1
Reviewer 1 Report
The paper "Solar Salt above 600oC: Impact of Experimental Design on thermodynamic stability results" is presenting the results concerning the influence of some parameters (components material, type and composition of purge gas, stiring speed, gas flow rate and so on) on the salt decomposition, and its stability at temperatures above 600oC.
It is seen that there is a lot of work behind, but the presentation of this work has some aspects that are disturbing.
1. The experimental test bench and procedure is literally described but the reader have to imagine how all the equipment’s are connected.
2. From the beginning, there is an annoying repeatedly auto-citing. 1/3 of the references are from the own group. I suppose that in the present paper should be presented the new things, and not to bring in front all the time the previous work and the previous results.
3. The presentation of the experimental design is missing (actually, as I said before, the work is about the influence, of some parameters, on the salt stability, at temperature above 600oC).
4. Most of the graphs can be summarized in stabilization time, and stabilization values, if there are any.
5. The results of the experiments although, they are individually detailed presented, it is difficult, at the end, to have an overview.
Because there are experimental results that are a pity to get lost, please reorganize the paper:
1 Add some minimal information, so the reader could understand without being redirect to some other papers. You may redirect the readers only for details or some specific things
2. Present in a concatenated manner the experimental design (factorial experiment), and experimental results.
3. Avoid annoying auto-citing
Author Response
Please check out Word file.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Ckeck for small gramar problems.
There are a few formating errors, such as font, please make sure all right.
Author Response
Thank you very much for your comments. We have reviewed the whole manuscript and eliminated the grammar mistakes according to your recommendation.
Reviewer 3 Report
The reviewed paper deals with thermal energy storage based on molten salts. An operating temperature of over 600 Centigrade is needed to produce electricity via a Rankine cycle with steam temperature up to 550 Cendigrade.
The understanding of salt parameters is essential here and the paper's authors demonstrate the behavior of melted salt with stable oxide ion concentrations at 620 Cendigrade.
Kindly take the following comments and inquiries into consideration:
1. The abstract provides useful information, the introduction section is clear to me, and the conclusion is informative too.
2. The figures could use some improvement. The font looks blurred and different in size (Fig 4 and 5 for example).
3. A bit unclear to me is a concentration mearing method. If it was well described in the previous papers, it is still respectful to the reader to add some info about it. Also, it will be nice to see the measured results with uncertainty if applicable.
In conclusion, I believe the revised manuscript can be published, but some minor revisions are necessary.
Yours sincerely,
The Reviewer.
Author Response
Please check out Word file.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Dear Authors,
further you may find some clarifications connected to your comments
Point 1.Thank you for your decision to add an explicative picture. Would have been nice if you would add a picture in which all the elements are at least presented in a legend. At the top of the experimental cell are a lot of elements which are not explained or have no connection with the text.
Point 2. Dear authors, self-citation is normal and welcome. I do appreciate your work and results. As I wrote previously “annoying repeatedly self-citation" is not about self-citation, but the way you do it. When writing a paper for objectivity and for emphasising the results, not the authors, it is written impersonally. More, I think you have in your culture a saying about self-promotion “eigenlob….”.
Point 3. I think that you misunderstood what I have said. Please make a difference between experimental setup and experimental design.
Point 4.The summarization of the graphs would have helped you with data interpretation, from the point of view of the user. More, for an experimental design and analysis you need some objective functions which, I think cannot be in a graph form.
Point 5. The concluding remarks, from conclusion chapter, emphasis what I have said, that the study is about the influence of some factors (materials, gases types, concetrations, pressures, velocity, and so on) on salt stability above 600oC. You presented partially in table 1 the experimental plan. I say partially because I do not see the influence of pressure, concentration and/or speed.
Point 2.2 Please read the point 3,4 and 5.
Point 3.2 Please read the point 2.
Author Response
Dear Reviewer,
Below you find our response to your comments.
Point 1. Thank you for your comment. We have improved the description of the experimental setup in Figure 1 accordingly.
Point 2. Thank you for your clarification. To tune the manuscript towards a more objective discussion, we change the wording (lines 71, 74, 88, 168, 172, 214, 220, 246, 310, 316, 443, 449, 495).
Point 3. Thank you for the clarification. We reviewed the manuscript and made sure, that "experimental setup" only is used, when discussing single components of the test rig. Further we included a specification in what context "experimental design" is used (see line 90 - 93).
Point 4. Thank you for your clarification. We modified table 1, so it will give and objective and usable summery of our results. In terms of the nitrate nitrite equilibrium, the equilibrium constant K1 is shown and can be used universally for every nitrate salt system. The oxide ion concentration is related to the respective nitrite concentration, which is related to the oxide ion equilibrium constant K2. We added an equation (Eq. 8) to clarify (see line 480). However, with the present data the exact stoichiometry in Eq. 8 is not accessible and future studies are needed to resolve this issue.
Point 5. Thank you for your comment. We have updated table 1 accordingly and made it clear which parameters were changed between the experiments. As mentioned in the discussion section 3.4. (line 418) change of equilibrium constant K1 is not very significant. The impact of the different experimental design (e.g. overpressure, NOx partial pressure, mixing velocity) is now accessible via the oxide formation rate given in table 1.
Round 3
Reviewer 1 Report
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