Experimental Investigation on Performance Enhancement of Parabolic Trough Concentrator with Helical Rotating Shaft Insert

Round 1

Reviewer 1 Report

Dear Authors,

thank you for your interesting work. The topic presented is really important and CSP technology should be further developed. Below you can find some comments regarding your work:

Experimental Investigation on Performance Enhancement of Parabolic Trough Concentrator with Helical Rotating Shaft Insert

1) Please avoid using abbreviations in an abstract ("PTC", "HTF"). Please introduce all abbreviations in the main part of the manuscript (for example in the section "Introduction").

2) Consider removing borders in the table on page 2

3) Consider adding a short comment at the end of line 59: "The examples of using twisted tapes have been shown in Ref. [17-24]" (or something like that to introduce the next paragraphs).

4) In my opinion, it is not the best explanation, why you discuss rotating helical shaft within a PTC receiver: "According to the existing literature, no other research uses this approach in PTC to our knowledge" (line 141). You can rather clearly point out the novelty and advantages of the proposed solution compared to existing systems. I suggest rewriting this sentence and including the paragraph regarding the contribution of your work to the actual state of the art. 

5) Please modify the structure of the manuscript. Chapter 2 should be "Materials and methods" and all information regarding the experimental rig, computational equations, and performance evaluation should be included as a subchapter (2.1, 2.2, and 2.3., respectively).

6) I think, that the word "photograph" is not a good option (line 144 and others). Please rewrite the sentences with this word to avoid using it. Furthermore, please consider moving Figure 1 and Figure 2 before point 2.1 (include these figures just after the paragraph with an included description of them /lines 144-146/). 

7) Please include units in the descriptions of quantities used in equations (if applicable). In line 282 it will be probably better to include values of efficiency as dimensionless numbers (0.327 instead of 32.7% and 0.80 instead of 80%)

8) I think it is not necessary to repeat the sentence "Experiments are performed over twenty-five sunny days (from  10:00 to 16:30) in June, July, and August) /line 306/. This information is included in lines 232-233.

9) In line 314 there is a lack of figure number: "The variation of Re with flow rate is presented in Fig. .". Also in lines 321, 328, 335, and 338 is the same situation. Furthermore, there is a problem with the figure included in line 320 (it is placed directly inside the paragraphs). Please fix these problems. 

10) Please carefully check and improve the numbers of figures in the manuscript. There are many mistakes with numbering them.

11) Please comment on the main conclusions resulting from data given in Table 6 Comparison between present work and various inserts inside PTC. 

12) Please include some numbers, when you present key findings in the Conclusions section.

13) Please discuss the practical aspects connecting with the introduction of the proposed solutions and the further works planned by the authors. What is the cost of the proposed system? Is it beneficial from an economical point of view?

Author Response

 "Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

Review on “Experimental Investigation on Performance Enhancement of Parabolic Trough Concentrator with Helical Rotating Shaft Insert”

by Allam et al.

Manuscrip​t ID Sustainability 1843783

 

 

A- General Comments

The paper in hand concerns outdoor experimental tests conducted to study the performance of a small-scale PTC equipped with a centrally placed rotating helical shaft. Three cases are studied; PTC without helical shaft insert, PTC with stationary helical shaft insert, and PTC with rotating helical shaft insert. The experiments are performed for different shaft rotational speeds (4, 11, and 21 RPM) and various flow rates (0.5, 1, 1.5, 2, and 2.5 LPM) of water as a heat transfer fluid (HTF). The fluid flow and heat transfer parameters (friction factor, Reynolds number, Nusselt number, and thermal enhancement factor) and performance parameters (thermal, overall, and exergetic efficiencies) are studied. Particularly, it was shown by the authors that the helical shaft insert had increased the required pumping power for the same flow rate. However, the PTC thermal performance has enhanced with the shaft rotational speed.

 

The topic of the paper is interesting, within the scope of the journal, and worthy of investigation. The originality of the work is acceptable and the study performed is adequate. However, the manuscript deserves a major revision. I suggest that authors take into account the comments and questions below before it can be accepted for publication in Sustainability.

 

 

B- Detailed Comments and questions

 

Title

The title is clear and consistent.

 

Abstract

1- More explicit (with numbers) results should be added to the end of the abstract.

2- Why the range of 4, 11, and 21 rpm is used for the shaft rotational speeds and 0.4, 1, 1.5, 2, and 2.5 LPM is used for the flow rate of water?

3- It is not clear whether the originality resides in the concept of inserts or the experimental setup and study performed to test the effect of inserts or both. Please clarify

 

Keywords

Keywords are ok.

 

1- Introduction

1- References relevant to Suatainability should be added, if possible.

2- There is a very good literature review presented. However, the originality of the work should be highlighted further at the end of the introduction.

 

2- Experimental Test Rig

1- This section is very well presented and complete. However, quality of figures 2 to 6 should be enhanced.

 

3- Computational Equations

1- I suggest to change the title to “Theoretical Background” or “Governing Equations”.

2- To the limit of my knowledge for applications involving heat transfer enhancement and pressure loss increase there are dimensionless factors like the thermal enhancement factor that takes into consideration the two effects simultaneously rather than each effect separately. What about your case? Why have you considered each parameter (thermal performance and Pressure Losses) separately?

 

 

4- Results and Discussion

1- More physical analysis are to be added to this section;

 

5- Conclusion

The main outputs of the manuscript in terms of applications should be highlighted.

 

6- References

References relevant to Sustainability should be added, if possible.

 

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors made a great effort on literature survey and case studies. However, the contributions of this paper need to be strengthened.  

1. The abstract can be imrpoved by highlighting contributions instead of neutrally stating the paper's content.  

2. More details of the experiment can be added.

3. In the case study and conclusion, the key findings are too ambiguous. Findings along with statistics are suggested. 

4. What are the future directions of this paper?

5. Please proofread the language to enhance the readability. 

Author Response

Comment #1: The abstract has been modified in the latest version.

Comment #2: More details of the experimental section has been re-arranged in the latest version.

Comment #3: Comment on Table 6 is modified to give extra explanation about the difference of the current study with different types of inserts ( starting with A comparison between the present work (static and rotating helical shaft) and different types of inserts in terms of thermal efficiency ratio, Nu number ratio, and friction ratio.....)

Moreover, a new section (4): "4. Economic Analysis" is added to estimate the total cost of three systems of PTC without a helical shaft, PTC with a stationary helical shaft, and PTC with a rotating helical shaft and make an evaluation to specify the beneficial system from an economic point of view.

These additions are covered also in the Conclusion section.

Comment #4: The last part of the Conclusion section  in the latest version (starting with: In the future, it is recommended to use nanofluids or hybrid nanofluids ....) has been added to cover the further work recommended by the authors.

Comment #5: The language, Figure, and equations numbers are revised and corrected.

 

Round 2

Reviewer 1 Report

Dear Authors,

I checked the paper and I am bit confused. Authors introduced many improvements, but the formatting of the manuscript is still terrible. For example: there is still a lack of proper numbering of figures. In my opinion the manuscript cannot be published in the current form. The authors have to carefully check the text: paragraph by paragraph and then send again the paper.

I attached version with a few comments.

Thank you in advance.

Comments for author File: Comments.pdf

Author Response

 "Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

Thank you for taking into consideration my comments and those of the other reviewer. The manuscript is now ready for publication.

Author Response

Thank you very much for your valuable comments.

Reviewer 3 Report

The reviewer has no more comments. 

Author Response

Thank you very much for your valuable comments.

Round 3

Reviewer 1 Report

Dear Authors,

thank you for your efforts put into improving the manuscript of your paper.