Dynamic Flow and Heat Transfer Characteristics of Uncracked Hydrocarbon Fuel under Super-Critical Pressure in the Cooling Channel of a Regeneratively Cooled Scramjet

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Enclosed you find a file with a list of remarks about the text, to correct misprints, errors, unclear passages. 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The quality of English is acceptable as a whole even though some sentences and words are not correct.

Author Response

Comments

Reviewer #1:

1. Abstract

line 11-12

As a result, dynamic process of flow and heat transfer in cooling channel is commonly occurred which may bring hazard and control difficulties for scramjet→. As a result, dynamic processes of flow and heat transfer which commonly occur in cooling channel may bring hazard and control difficulties for scramjet. (suggestion)

line 15

, which includes change of inlet →, including change of inlet

line 18

are about 12.5 s. → is about 12.5 s. (why a specific information like this in the abstract?).

Answer: Thank you for your valuable suggestion. Line 11-12, line 15, line 18 have been modified with suggestions of Reviewer 1. Reason of providing a specific information like 12.5s is that the authors have been told to provide important data in abstract in our revision of previous paper. After that, authors always mention important data in abstract. For the convenient of rewires and editor, the modified Abstract is attached below:

Abstract: Regeneratively cooled scramjet has already been successfully verified as propulsion device for hypersonic vehicle. As a result, dynamic process of flow and heat transfer in cooling channel is commonly occurred which commonly occur in cooling channel may bring hazard and control difficulties for scramjet. To study transient flow and heat transfer process in cooling channel, a dynamic numerical model is established. Dynamic characteristics of flow and heat transfer under different conditions are calculated and discussed, including change of inlet fuel mass flow, heat flux and pressure working conditions. Results show that stable time of cooling channel outlet fuel temperature is related to the change rate of inlet mass flow and heat flux. The stable time of outlet fuel temperature under heat flux decreasing working conditions are about 12.5 s. The initial response of working pressure fluctuation will lead to fuel temperature fluctuation, which has little effect on wall temperature.

 

2. Introduction

line 31

imposing substantial heat load for body of scramjet→ are imposing substantial heat load for body of scramjet

line 40

a liquid hydrocarbon fuel scramjet and → a liquid hydrocarbon scramjet fuel

line 48-50

Meanwhile scramjet….and working pressure→ the long sentence is quite confused, please check grammatical structure

line 62

Significance of the convective heat transfer coefficient→ Because of the significance of the convective heat transfer coefficient

line 83

carbon fuel experiences heavily change in pseudo-critical region, especially specific → carbon fuel experience heavily change in pseudo-critical region, especially for specific

Line 89

is establish to control→ is established to control

Answer: Thank you for your valuable suggestion. Line 31, line 40, line 62, line 83 and line 89 have been modified with suggestions of Reviewer 1. Line 48-50, the long sentence is rewritten. The detailed modifications are colored blue in the manuscript.

3. Numerical model and calculation scheme

Line 98

as depicted in Fig. 3.→ as depicted in Fig. 3 as geometry is concerned.

Line 111

adhere to the conservation law→ depend on the conservation law

line 114-115

adopts the 18 species 24 model→18 species 24?? Is 24 a misprint or what does it mean?

Line 120

the following equations (Eq.5, Eq.6) can be derived:→ do you refer to previous equations or do you mean eqs. 8 and 9?

line 138

of the radial fuel temperature distribution in the cooling channel → of the radial distribution of fuel temperature in the cooling channel

Line 150

For the convenient, the overall→ For the convenience, the overall

line 153

the average fuel and wall temperature are monitored → the average fuel and wall temperatures are monitored

line 172

22], which is shown in Fig. 4. → 22], as shown in Fig. 4

Line 173

Fig. 4. Iterative Solution Process for Temperature→ which temperature? In general, or for a specific case?

Line 176

Three different dynamic conditions→ The three different dynamic conditions

line 179

In the initial boundary conditions of the study, the stable conditions are considered. → The stable conditions are considered as initial boundary conditions of the study,.

line 201

when the number of grids reached → when the number of grid nodes reached

line 204

independent stare.→ independent state

line 205

the chosen grid size of 70,000 grids→ the chosen grid size of 70,000 nodes

line 226-227

Table 3 accompany the setup provides information → Table 3 accompanying the setup of Fig.6 provides information

Line 233

The elements of eq. (25) are not included in the nomenclature ? a?→ such equation has to be discussed, also for the following use

Answer: Thank you for your valuable suggestion. Line 98, line 111, line 138, line 150, line 153, line 172, line 176, line 179, line 201, line 204, line 205 and line 226-227 have been modified with suggestions of Reviewer 1. In line 114-115, 24 means 24 steps, which is step number of chemical reaction. In line 120, eq. 5 and eq. 6 are incorrect, which are correct to eq. 8 and eq. 9. In line 173, temperature is the Cross-sectional Average Fuel Temperature, which is corrected in manuscript. In line 233, elements of Eq. 25 have been added in nomenclature. The detailed modifications are colored blue in the manuscript.

4. Results and discussion

Line 266

stable fuel temperature gradually decreases (Fig. 8b).→ Il figure 8 Δr is referred to inlet mass flow but it is neither included in the nomenclature nor straightforward. It should be added.

Line 274

the steady velocity decreases; With two→ the steady velocity decreases; with two

line 277

with the constant of inlet temperature→ with a constant inlet temperature

Line 310

heat transfer coefficient show a trend of decrease→ heat transfer coefficient shows a trend of decrease,  

line 311

Such a trend is attribute to the decrease → Such a trend is attributed to the decrease 

line 314

in the 2~6 s. Such a trend is attribute to the increase → in the 2~6 s timespan. Such a trend is attributed to the increase

Line 315-316

was larger than the decrease of the partial derivative of the adjacent wall fuel temperature. → the comparison of a difference with a derivative (also beforeand after) should be better explained 

line 319

trend is attribute to the increase→ trend is attributed to the increase

line 323

1~4 s. The effect→1~4 s timespan. The effect

line 359

decreases and then increases→ decreases and then increases again 

line 361

Such a trend is attribute to the → Such a trend is attributed to the 

Line 365

Such a trend is attribute to the increase-→ Such a trend is attributed to the increase- 

Line 368

in the first 1~4 s. Such a trend is attribute to the increase → in the first 1~4 s timespan. Such a trend is attributed to the increase 

line 418

Such a trend is attribute to the increase → Such a trend is attributed to the increase

Answer: Thank you for your valuable suggestion. Line 274, line 277, line 310, line 311, line 314, line 319, line 323, line 359, line 361, line 365, line 368 and line 418 have been modified with suggestions of Reviewer 1. Because there are two types rate of change, rate of change of fuel mass flow and rate of change of heat flux. Explanation of rate of change is divided into two parts, the first part is Δr, second part is subscripts, in which m represents fuel mass flow and qf represents heat flux. Both of them are provided in nomenclature. Furthermore, ‘the partial derivative of the adjacent wall fuel temperature’ in line 315-316 is plotted in Fig. 11a and 11b, which is explained in manuscript.

5. Conclusions

line 439

at different Tfoi is almost →. at different T_foi is almost

line 442

with the change of working pressure than wall temperature → to the change of working pressure than to wall temperature

Answer: Thank you for your valuable suggestion. Line 439 and line 442 have been modified with suggestions of Reviewer 1.

6. Nomenclature

eff, exp, foi → in subscripts section.

Answer: Thank you for your valuable suggestion. eff, exp, foi are changed in subscripts section.

7. References

Minor inaccuracies:

Ref. 1,3,4,5,6,8,10,11,12,13,14,15,18,19,21,22,23,24. → In all these cases the list of authors is incomplete, “et. al.” is correct in recalling the paper but not in reporting the information about the same paper, The entire list of authors should be provided, it is not so difficult.

Answer: Thank you for your valuable suggestion. List of authors in Ref. 1, 3-6, 8, 10-15, 18-19, 21-24 have been modified with suggestions of Reviewer 1.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript Number: applsci-2870958-v1

Full Title: Dynamic Flow and Heat Transfer Characteristics of Uncracked Hydrocarbon Fuel under Super-Critical Pressure in Cooling Channel of Regeneratively-Cooled Scramjet

 

I – General Comments

The present manuscript numerically investigates dynamic characteristics of transient flow and heat transfer characteristics of hydrocarbon fuel in a cooling under different conditions. The analysis includes change of inlet fuel mass flow, heat flux and pressure working conditions. There are recommendations/questions addressed to the authors, before to accept their manuscript as Applied Science’s paper.

 

II - Specific Comments

(i) In “Abstract”: The main contribution of the present work must be better clarified and the present state of the art concerning the investigated topic must also be introduced and contextualized. It is unclear the intended publication in AS.

(ii) In “Introduction”: It is necessary attention for the following aspects: (a) it must state the motivation for doing a research and what it will contribute to the research field; and (b) it must present a description of the exact question or hypothesis that the paper will address including a brief summary of the adopted methodology to solve the problem. Thus, the authors must complete the “Introduction” into this context to clarify the importance of their methodology for purposes of engineering practical applications and also to justify the intended publication in AS. It is not recommended the use of Figures into the Section 1 too.

(iii) Most of References are outdated. Please use /add more up to date references. Moreover, the manuscript needs some citations.

(iv) When starting “Section 2”, it is necessary to link the problem representative figure with the mathematical formulation (the assumed hypothesis, governing equations and boundary conditions). It is important some comment about the assumed hypothesis and their consequences for the mathematical formulation too.

(v) Equations must be referenced into the manuscript.

(vi) It is recommend a Table summarizing the value of different constants appearing into the mathematical formulation. There is some confusion with the definition of some constants.

(vii) In Figure 7, numerical results seem disperse from experimental results for x-axis < 200 mm and for x-axis > 550 mm. It is recommended to include some physical discussion for that behavior.

(viii) Experimental result must be referenced in Figure 7. What are the uncertainties from the experimental results presented in Figure 7?

 

(ix) It is recommended some discussion concerning the Mach number sensitivity for the investigated problem.

(x) The analyses concerning the influence of inlet fuel mass flow, heat flux and working pressure need more some integration. It would be better if a baseline method is available and compared with the present model (if possible). The purpose is to demonstrate the new features, benefits, and advantages of the adopted method.

(xvi) In “Conclusions”: It is necessary to include comments with respect the numerical/experimental results behaviour as compared as previous works (specially, experimental data of reference). The readers need to be better convinced of the novelties from present work.

(xvii) In closing, it is important to complete “Conclusions” with perspectives for a future research. What are the drawbacks in this numerical method? And what are the ways to resolve them? More details should be provided. Finally, the main contribution of the present manuscript should be clarified aiming to justify its publication in AS.

 

III - Recommendation for the Applied Sciences´ Editor

In my opinion, the present manuscript needs attend all topics above presented. Upon consideration of all points above, I think the paper could be considered for publication in Applied Sciences.

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Comments

Reviewer #2:

1. In “Abstract”: The main contribution of the present work must be better clarified and the present state of the art concerning the investigated topic must also be introduced and contextualized. It is unclear the intended publication in AS.

Answer: Thank you for your valuable suggestion. The abstract has been modified according to comment of Reviewer 2. The detailed content is colored blue in the manuscript.

 

2. In “Introduction”: It is necessary attention for the following aspects: (a) it must state the motivation for doing a research and what it will contribute to the research field; and (b) it must present a description of the exact question or hypothesis that the paper will address including a brief summary of the adopted methodology to solve the problem. Thus, the authors must complete the “Introduction” into this context to clarify the importance of their methodology for purposes of engineering practical applications and also to justify the intended publication in AS. It is not recommended the use of Figures into the Section 1 too.

Answer: Thank you for your valuable suggestion. The introduction has been modified according to comment of Reviewer 2. Using figures in introduction is to help readers comprehend working process of regenerative cooling process and the specific property changes of hydrocarbon fuel. The detailed content is colored blue in the manuscript.

 

 

3. Most of References are outdated. Please use /add more up to date references. Moreover, the manuscript needs some citations.

Thank you for your valuable suggestion. The references have already been updated according to comment of Reviewer 2. Now more than 1/3 of the references are published in latest 5 years. The detailed content is colored blue in the manuscript.

 

4. When starting “Section 2”, it is necessary to link the problem representative figure with the mathematical formulation (the assumed hypothesis, governing equations and boundary conditions). It is important some comment about the assumed hypothesis and their consequences for the mathematical formulation too.

Answer: Thank you for your valuable suggestion. The sectional structure has been explained with Fig. 3. The governing equations are introduced with structure of Fig. 3. The detailed content is colored blue in the manuscript.

 

5. Equations must be referenced into the manuscript.

Answer: Thank you for your valuable suggestion. All the Equations have already been referenced in the manuscript. The detailed content is colored blue in the manuscript.

 

6. It is recommend a Table summarizing the value of different constants appearing into the mathematical formulation. There is some confusion with the definition of some constants.

Answer: Thank you for your valuable suggestion. Definitions have already been covered in the Appendix A: Nomenclature at the end this manuscript. The detailed content is colored blue in the manuscript.

 

7. In Figure 7, numerical results seem disperse from experimental results for x-axis < 200 mm and for x-axis > 550 mm. It is recommended to include some physical discussion for that behavior.

Answer: Thank you for your valuable suggestion. The result for x-axis < 200 mm and for x-axis > 550 mm has been explained in the manuscript. The detailed content is colored blue in the manuscript.

 

8. Experimental result must be referenced in Figure 7. What are the uncertainties from the experimental results presented in Figure 7?

Answer: Thank you for your valuable suggestion. The result has already been plotted in Fig. 8, which is written as T_w,exp. While the uncertainties are provided in Table 4. The detailed content is colored blue in the manuscript.

 

9. It is recommended some discussion concerning the Mach number sensitivity for the investigated problem.

Answer: Thank you for your valuable suggestion. It is very meaningful idea of considering Mach number in this manuscript. Influence of Mach number is through heat flux generated from combustion, which heavily replies on geometry of combustor and aerodynamic parameters. These are hardily cover in a single research paper. To avoid confusions and complexities aroused by geometry and aerodynamics, the heat flux in this manuscript is independent from Mach number. As a result, a wider range of results can be obtained in which contains the flight Much number range. In our future work, influence of Mach number on dynamic flow and heat transfer characteristics shall be taken into carefully study.

 

10. The analyses concerning the influence of inlet fuel mass flow, heat flux and working pressure need more some integration. It would be better if a baseline method is available and compared with the present model (if possible). The purpose is to demonstrate the new features, benefits, and advantages of the adopted method.

Answer: Thank you for your valuable suggestion. The benchmark cases have been provided at the beginning of 31, 3.2 and 3.3, which are colored blue in the manuscript.

 

11. In “Conclusions”: It is necessary to include comments with respect the numerical/experimental results behaviour as compared as previous works (specially, experimental data of reference). The readers need to be better convinced of the novelties from present work.

Answer: Thank you for your valuable suggestion. In the conclusion part, research in this manuscript has been summarized, the relationship between this work and our previous works has been explained. The modifications are colored blue in the manuscript.

 

12. In closing, it is important to complete “Conclusions” with perspectives for a future research. What are the drawbacks in this numerical method? And what are the ways to resolve them? More details should be provided. Finally, the main contribution of the present manuscript should be clarified aiming to justify its publication in AS.Could you specify which aspects of the proposed model distinguish it from existing work?

Answer: Thank you for your valuable suggestion. The time partial derivative terms are taken into consideration, which is different from our previous work. The thermo-physical property calculation model is derived from our previous work, which is proved to be effective. In the discussion part, heat transfer coefficient is studied and discussed, which is calculated with our calculation method proposed in Ref. 22. As a result, the flow and heat transfer dynamic model is different from our existed work.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents a study of transient flow and heat transfer process in a cooling channel of a Scramjet. The topic is interesting, nevertheless, there are some issues that need to be addressed by the authors:

- The following questions must be answered in the abstract section: What and how was it done? Why was the study done? What was found? What do these findings mean and what impact do they have? In this sense, it is not clear the propose of the study as well as the impact of the results.

- A real image of the system will be very useful for the reader.

- Figure 1 and 2 are not mention in the main text. All the figures must be mentioned in the main text.

- The knowledge gap that the manuscript tries to fulfill need to be better highlighted.

- At the end of the introduction section, add a sentence about the importance of carrying out this research.

- Justify that the geometry used is representative of the real device.

- Justify the use of the Peng-Robinson model.

- Figure 8. Adding ranges of change in figure legends can cause confusion.

- Figure 9. The axis label is too close to the image.

- The results are discussed in a very general form. A more quantitative way is preferred rather than qualitative.

- At the end of the conclusion section, add recommendations, future works and the usefulness of the results to the scientific community.

Author Response

Comments

Reviewer #3:

1. A real image of the system will be very useful for the reader.

Answer: Thank you for your valuable suggestion. A picture of real system has been added as Fig. 7 in the manuscript. The detailed modifications are colored blue in the manuscript.

 

2. Figure 1 and 2 are not mention in the main text. All the figures must be mentioned in the main text.

Answer: Thank you for your valuable suggestion. Fig. 1. And Fig. 2. have been cited in the manuscript. The detailed modifications are colored blue in the manuscript.

 

3. The knowledge gap that the manuscript tries to fulfill need to be better highlighted.

Answer: Thank you for your valuable suggestion. The importance of the knowledge gap in this manuscript has been proposed in abstract, conclusiont and highlights. The detailed modifications are colored blue in the manuscript.

 

4. At the end of the introduction section, add a sentence about the importance of carrying out this research.

Answer: Thank you for your valuable suggestion. The importance statement of this manuscript has been added at the end of introduction. The detailed modifications are colored blue in the manuscript.

 

5. Justify that the geometry used is representative of the real device.

Answer: Thank you for your valuable suggestion. A picture of real system has been added as Fig. 7 in the manuscript. The detailed modifications are colored blue in the manuscript.

 

6. Justify the use of the Peng-Robinson model.

Answer: Thank you for your valuable suggestion. The P-R EoS is proposed by Chung, which has been extensively applied in the research of heat exchange of hydro-carbon fuel. This method has been proved to be effective and accurate in calculations of physical properties with a lot of research and papers. The explanation for use of P-R EoS has been added in the manuscript. The detailed modifications are colored blue in the manuscript.

 

7. Figure 8. Adding ranges of change in figure legends can cause confusion.

Answer: Thank you for your valuable suggestion. The ranges in Fig. 8 has been adjusted. The detailed modifications are colored blue in the manuscript.

 

8. Figure 9. The axis label is too close to the image.

Answer: Thank you for your valuable suggestion. The axis label in Fig. 8 has been adjusted. The detailed modifications are colored blue in the manuscript.

 

9. The results are discussed in a very general form. A more quantitative way is preferred rather than qualitative.

Answer: Thank you for your valuable suggestion. In the discussion part, precisely data have been provided for result discussion. Since there are plenty of results and figures in this manuscript, the author sincerely hope that reviewer help us to find the specific unclear explanations for the result.

 

10. At the end of the conclusion section, add recommendations, future works and the usefulness of the results to the scientific community.

Answer: Thank you for your valuable suggestion. Future works has been added at the end of the conclusion. The detailed modifications are colored blue in the manuscript.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

the suggestions requested

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Comments

Reviewer #4:

1. Could you specify which aspects of the proposed model distinguish it from existing work?

Answer: Thank you for your valuable suggestion. The time partial derivative terms are taken into consideration, which is different from our previous work. The thermo-physical property calculation model is derived from our previous work, which is proved to be effective. In the discussion part, heat transfer coefficient is studied and discussed, which is calculated with our calculation method proposed in Ref. 22. As a result, the flow and heat transfer dynamic model is different from our existed work.

 

2. Include nomenclature with SI units.

Answer: The symbols in nomenclature are all written in SI units

 

3. Briefly outline the advantages of your methodology and include it in the manuscript.

Answer: Thank you for your valuable suggestion. The advantages of methodology in this paper has been outlined at the end of introduction. The detailed content is colored blue in the manuscript.

 

4. What are the benchmark cases in your study?

Answer: Thank you for your valuable suggestion. The benchmark cases have been provided at the beginning of 31, 3.2 and 3.3, which are colored blue in the manuscript.

 

5. What finding did the author obtain as a scientific novelty for the first time in this article?

Answer: Thank you for your valuable suggestion. The scientific novelty has been added in conclusions (1) and (2), which are colored blue in the manuscript.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript Number: applsci-2870958-v2

Full Title: Dynamic Flow and Heat Transfer Characteristics of Uncracked Hydrocarbon Fuel under Super-Critical Pressure in Cooling Channel of Regeneratively-Cooled Scramjet

 

The original text of the manuscript has been satisfactory revised. In my opinion, the manuscript can be published as Applied Science’s paper.

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Thank you for your valuable suggestion.  English language of this munuscript has been conducted. The detailed content is colored blue in the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

Most of the issues have been addressed by the authors. Nevertheless, there are some remaining issues that need to be addressed.

In the first part of the Introduction section and some parts of the manuscript, a legend 'Error! Reference source not found' appears. Did the authors check this before submitting the paper?

There are two Figures 7. What is the difference between them?

The authors included an image of the real device, but they did not provide justification for why the geometry used in the simulation is representative of the real device. It's important for the authors to ensure that their responses to reviewers' comments are carefully considered and not merely duplicated.

Author Response

Thank you for your valuable suggestion. The relation between real structure and model in this manuscript has been added. Because of the wrong set of software, some errors of format have occured. They are all been corrected. Authors are appologise for these errors. The detailed content is colored blue in the manuscript.