Assessment of the Thermo-Hydraulic Efficiency of an Indoor-Designed Jet Impingement Solar Thermal Collector Roughened with Single Discrete Arc-Shaped Ribs

Round 1

Reviewer 1 Report

The research is extension of Kumar et al., however the research gap is interesting, authors need to clarify the following:

1. The application of this research is on solar, however, there is no utilization of solar in the manuscript, instead a heater was installed to provide heat (which is ok), but the authors did not provide justification on their selection of heater power (1000 W/m^2), how this relates to the available solar radiation received. Also please explain if the heat was constant or varied, and explain why?
2. Many thermocouples were installed, authors need to explain did they average the temperature readings, also to justify the averaging since there are many thermocouples so why its averaged.
3. Please provide details of beta value in equation 6.
4. Authors used Darcy equation which is for fully developed flow, but they did not show if the flow was fully developed, please provide details to show the flow was fully developed.
5. In the validation of experimental against fundamental correlations in equations 2 & 3, Dittus-Bolter and Blasius equations were used which have limitations in its implementation, please explain why it was used. Again, justification that you have fully developed flow.
6. Authors used Dittus-Bolter and Blasius in their validation, but they used Darcy equation to determine friction factor for their results, why? We are aware that Dittus-Bolter and Blasius correlation are suitable for smooth surface, but how it compares when you use Darcy in your validation.
7. Critical analysis is needed on the results to justify why there is little change in Nusselt and friction factor with respect to Reynolds for smooth surface as compared to other cases (Sdr cases).
8. Pressure drop is the important factor that should be looked at, although results presented were based on friction factor which is related to pressure drop but authors need to justify why they did not use pressure drop which can be useful for the application of Jet Impingement Solar Thermal Collector and from this drop the power utilized to overcome the loss in pressure could be determined.
9. It appears from the range of Reynolds presented that the flow could be considered in the transient and turbulent range, please justify the tested range and why laminar flow was not included.
10. Please present your results in the conclusion in percentage, i.e. increase/decrease by …..% rather than presenting it by highest which do not show the increase/decrease.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

The article deals with a topic of current interest that concerns the journal scope.

The article is well structured and the experimental data are based on a seemingly adequate test bench.

Overall the article is potentially interesting.

However, the following observations should be addressed in order for the article to be recommended for publication.

Major comments

1. Table 1 lists together values and ranges of both dimensionless geometric variables and Reynolds number used during the tests. The table title should distinguish between geometric variables and physical variables.
2. An essential advantage of using dimensionless variables is their ability to generalise results, provided that the full list of dimensionless variables is specified. Table 1 lists 12 lengths and one angle as geometrical parameters, but only the values adopted for 8 dimensionless ratios Dd/Lv, gw/Hr, Hr/H,..., X/Dhy,... and one angle are given. For the geometry to be fully defined, another 4 dimensionless ratios are required.
3. Is it necessary to add other geometrical parameters listed in the nomenclature and the corresponding dimensionless ratios to the list? For example, W or areas Ap, Af, Ao.
4. Also, all temperatures involved in the experiment and listed in the nomenclature are boundary conditions or variables that give rise to dimensionless ratios.
5. The Mach number is another dimensionless physical variable that can have an influence in phenomena with compressible fluids and complex geometry, where local pressure-related interferences can occur. In the Introduction section, the authors cite references where the influence of Mach number is mentioned, but the article does not provide further information on this issue.
6. On the other hand, the lengths used as reference in Reynolds numbers, Nusselt and friction factor must be clearly specified.
7. Given the physical and methodological analogies, it seems advisable for the authors to consult the reference https://doi.org/10.1016/j.renene.2012.03.025.
8. It would be advisable that tables with experimental results are available as Supplementary Data in a repository.
9. Figures 5 and 6 are the same as the ones previously published in https://doi.org/10.1016/j.seta.2021.101523.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I have carefully reviewed the revised manuscript and responses to reviewer's comment and found that the authors have adequately and properly responded to the comments and made all required revisions to the manuscript based on the comments.

responded 

Author Response

Response to the Reviewers

Dear Sir,

We all authors are very grateful to the reviewers for their valuable comments/suggestions which helps us to improve the manuscript.

We have revised the manuscript according to the reviewer suggestions/comments.

Reviewer -1

I have carefully reviewed the revised manuscript and responses to reviewer's comment and found that the authors have adequately and properly responded to the comments and made all required revisions to the manuscript based on the comments.

Response: Thanks. The manuscript is thoroughly checked for spelling mistakes. The suggested changes are incorporated in the revised manuscript.

Reviewer 2 Report

Overall, the authors have responded satisfactorily to the observations previously made.
However, there are the following errors which should be corrected, without the need for further revision of the article.

Minor comments:

• The length D_hy is used as the reference length in the Reynolds and Nusselt numbers. In various parts of the article it appears either in upper or lower case. The notation should be unified or any errors should be corrected.
• References (37) and (38) are the same. The numerical list of references should be corrected.

Author Response

Response to the Reviewers

Dear Sir,

We all authors are very grateful to the reviewers for their valuable comments/suggestions which helps us to improve the manuscript.

We have revised the manuscript according to the reviewer suggestions/comments.

Reviewer-2

Comments and Suggestions for Authors

Overall, the authors have responded satisfactorily to the observations previously made.
However, there are the following errors which should be corrected, without the need for further revision of the article.

Minor comments:

The length D_hy is used as the reference length in the Reynolds and Nusselt numbers. In various parts of the article it appears either in upper or lower case. The notation should be unified or any errors should be corrected.

References (37) and (38) are the same. The numerical list of references should be corrected.

Response: The suggested changes are incorporated in the revised manuscript.