Performance Assessment and Heat Transfer Coefficient of Antifreeze Fluids in Low-Temperature Solar Collectors

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study conducts a comparative performance analysis of three different low-temperature solar collector systems: Flat Plate Solar Collectors (FPC), Heat Pipe Evacuated solar Collectors (HPETC) and Heat Pipe Flat Plate Collectors (HPFPC). The research content reflects certain innovation, but there are some issues need be further improved.

1. Please provide a more detailed explanation of the heat transfer coefficient calculation methods for various types of collectors, especially HPFPC, as this is a key parameter.
2. Explaining the performance differences of HPFPCs when using antifreeze and water may involve the interaction between fluid physical properties and collector design.
3. Expand the introduction section to discuss more about the application background of low-temperature solar collectors, especially the necessity of using antifreeze in cold climates.
4. Researching the use of specific environmental conditions for simulation, it is recommended to discuss how solar radiation and environmental temperature changes affect the performance of collectors.
5. Suggest discussing the use of mixed or mixed fluid systems to optimize performance under different operating conditions.
6. The paper will provide a more detailed explanation of the heat pipe operation in HPFPC, as this technology is relatively new and may not be familiar to some readers.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a comparative analysis of low-temperature solar collectors using different heat transfer fluids, focusing on efficiency and heat transfer coefficients. While the study is well-structured and provides valuable insights, some aspects require further clarification, particularly in the modeling assumptions and validation process.

1. Thermal Efficiency Trends:

   • The study finds that the efficiency of HPFPC decreases significantly with higher antifreeze concentrations. Could this be mitigated by modifying the heat exchanger design or using a different pipe material?

2. Choice of Heat Transfer Fluids:

   • Why were ethylene glycol and propylene glycol specifically chosen, and were any alternative antifreeze solutions considered?
   • Have you evaluated the environmental impact of these fluids, particularly regarding potential leakage or disposal?

3. Numerical Model Validation:

   • The validation results show a maximum error of 6.2%. Could this discrepancy be attributed to uncertainties in material properties or fluid dynamics assumptions?
   • Have sensitivity analyses been conducted to determine which parameters have the most significant effect on the model’s accuracy?

4. Practical Applications & Cost Analysis:

   • How do the cost and operational feasibility of HPFPC compare with traditional FPC and HPETC in real-world installations?
   • Would a combination of different antifreeze fluids offer better efficiency while maintaining freeze protection?

5. Heat Transfer Coefficient Reduction:

   • The study reports a 28–41% reduction in the heat transfer coefficient with antifreeze use. How does this compare with previous experimental findings?
   • Could this reduction be counteracted by increasing the flow rate or using an external heat recovery system?

Comments on the Quality of English Language

The quality of the English language in the manuscript is generally good, but there are some areas that could be improved for better clarity, readability, and grammatical accuracy. Some sentences are too long or complex, which may affect comprehension. Additionally, there are minor grammatical errors, awkward phrasing, and inconsistent use of technical terms. A thorough proofreading and linguistic refinement would enhance the fluency and overall readability of the paper.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript has investigated the thermal performance of these systems using different heat transfer fluids, specifically water, and mixtures of 30% and 50% ethylene glycol and propylene glycol. However, the manuscript requires MAJOR REVISION before it is considered for publication. Thus, the authors should revise the manuscript accordingly. The following hints may help the authors：

Q1: The writing and grammar should be extensively improved. The current version of the manuscript is hard to read because it is very poorly written. I encourage the authors to work with an English speaker in order to improve the readability of the text. In addition, the tense of a sentence should be improved. Many grammatical errors were found. For example:“The same author [27] presented later a theoretical and experimental work for the same conditions, obtaining good agreement and showed that the number of wickless heatpipes has a …”

Q2: In paper, please summarize the main contribution of each references paper in separate sentences，such as [4-6]. The reference style should be checked again according to the journal standard.

Q3: In the section 2.2, error analysis should be conducted.

Q4: In the equations and paper, the variables represented by letters should be italicized.

Q5: The conclusion and Abstract are not well organized and should be improved.

Q6: There are many abbreviations in the article, and it is very useful for the author to add a nomenclature. Abbreviations appearing for the first time in an article should be used in full, and the abstract is no exception.

Q7: The paper lacks innovation. The authors must highlight their own findings from literature review.

Q8: The Discussion and Results section is written too simply, and the authors are advised to rewrite the Discussion and Results section. This paper cannot provide meaningful conclusions to the author.

Comments on the Quality of English Language

Please see the Comments and Suggestions for Authors.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1. The results of model mesh generation should be added to the main text.​
2. The accuracy verification of the model should be carried out.​
3. It is recommended to state the conclusions separately.​
4. Discussions should be added to indicate the practical guiding significance of the research for engineering.​
5. The fonts in the pictures should be unified.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have made notable improvements to the manuscript. However, the introduction does not present current issues in detail. Therefore, I ask the authors to cite and describe recent work on the topic. Among these articles, I suggest mentioning the following:

• Three-dimensional numerical analysis of the impact of the orientation of partially inclined baffles on the combined mass and heat transfer by a turbulent convective airflow

https://doi.org/10.1007/s40095-022-00505-5 

• Analysis of the thermohydrodynamic behavior of a cooling system equipped with adjustable fins crossed by the turbulent flow of air in forced convection

https://doi.org/10.1007/s40095-021-00446-5 

 

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have carried out a thorough and careful revision and the revised manuscript improved a lot in terms of technical quality and language. Therefore, I would recommend it for publication in the Journal.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf