Numerical Analysis on the Heat Transfer Characteristics of Supercritical Water in Vertically Upward Internally Ribbed Tubes
Round 1
Reviewer 1 Report
The submitted manuscript presented a comprehensive numerical analysis of heat transfer characteristics in vertically upward internally ribbed tubes. Although the topic of research is not new but would be interesting in the relative scientific community for its findings and analysis through numerical simulations. The numerical model used in this research has been validated with the experimental data. The results were presented with sufficient discussions. The research has been well documented. 24% similarities were detected in Turnitin Plagiarism check, but those mostly from the common technical terms. The findings are summarized in the conclusion section, mostly as a qualitative summary. This section can be further improved by adding quantative findings. The authors are requested to add a section on the future scopes of research to create interest among the readers and assist the respective research community to explore future possibilities.Author Response
Answer: Many thanks for your careful review and positive affirmation on our study. According to your valuable suggestion and comments, we have revised the abstract and conclusions. Moreover, a new section on the future scopes of research have been added in the end of our revised paper. All revisions are highlighted with yellow color in the revised manuscript.
Reviewer 2 Report
The paper is well arranged in general and topic is interesting. My comments are
- There is no nomenclature and it should be arranged and parameters should be defined.
- I am curious about the assumptions of the governing equations, is there any assumptions in those equations? If yes please add them to the text.
- I think that a table should be given and all thermo-physical properties of fluid should be given. If they change with temperature, equations should be written.
- I did not see heat conduction equation for the solid means ribs and pipe. Can it be explained?
- I do not know that the plotted velocity profile belongs to which position in the tube. If the authors study fully develop flow, where is the end of entrance region.
- The first letter in Figure captions should be capital
- In Figure 4, what are those experimental results? They belong to how? Any refence? Are the all conditions such as size etc between numerical and experimental the same?
Author Response
Thanks for your careful review and valuable comments on our manuscript. According to your valuable suggestion and comments, we have revised all mistakes accordingly. Nomenclature table have been added as your suggested. Assumptions of the governing equations and the figure on thermophysical properties were added. All revisions are highlighted with yellow color in the revised manuscript.
- There is no nomenclature and it should be arranged and parameters should be defined.
Answer: Thanks for your good suggestion. A nomenclature table covered important parameters have been added in the end of our revised manuscript.
- I am curious about the assumptions of the governing equations, is there any assumptions in those equations? If yes please add them to the text.
Answer: Sorry, we did not make it clear. There is some assumptions of the governing equations. We have added them into (2.1 physical model).
Two assumptions have been made. First of all, thermophysical properties is assumed as the function of temperature but ignored the effect of pressure variation in this model. Secondly, the added heat flux is assumed to be uniformly distributed along the in the whole pipe circumference.
- I think that a table should be given and all thermo-physical properties of fluid should be given. If they change with temperature, equations should be written.
Answer: Thanks for your good comments. To describe the special variation of thermophysical properties of supercritical fluids, a new Figure has been added in our revised paper.
Obviously, as seen in Figure 4, a steep variation of thermophysical properties presents in the pseudocritical region. It is necessary to introduce complex state equation to describe such steep variation. The corresponding equations are very complex, especially in the near-critical region. In our model, we called the NIST(National Institute of Standards and Technology) Refprop database to solve these equations and got the thermophysical properties, such as specific-heat, density, thermal-conductivity, and viscosity.
- I did not see heat conduction equation for the solid means ribs and pipe. Can it be explained?
Answer: Thanks for your good comments. A general transport equation for energy is shown in Eq.(3) in our manuscript, which can be solved the temperature/enthalpy distribution in the solid and fluid region. When this equation applied in the solid region, the corresponding velocity becomes zero, thus Eq.(3) can be simplified to a conduction equation.
- I do not know that the plotted velocity profile belongs to which position in the tube. If the authors study fully develop flow, where is the end of entrance region.
Answer: That is a very good question. All plotted velocity profiles are located in the bulk enthalpy of 1950 kJ/kg. As seen in Figure 6, it is almost in the middle of our test section, which is far from the entrance region.
- The first letter in Figure captions should be capital.
Answer: Thanks for your good comments. We have checked all Figure captions carefully and revised some figure captions.
- In Figure 4, what are those experimental results? They belong to how? Any refence? Are the all conditions such as size etc between numerical and experimental the same?
Answer: Sorry, we did not make it clear. Here we used the experimental data from our laboratory, and these experimental result has been published in the Journal and thesis. The corresponding rib structure and operating parameters are identical with our simulation model. In our revised papers, the corresponding citations have been added in Fig. 4 as a reference.
Reviewer 3 Report
See attached file
Comments for author File: 
Comments.pdf
Author Response
We very much appreciate your careful reviewing of our manuscript and your valuable comments. We have carefully revised the manuscript according to your comments. All revisions are highlighted with yellow color in the revised manuscript.
- The abstract is very descriptive. Please, introduce some quantitative results of your work!
Answer: Thanks for your comments. In our revised manuscript, some quantitative results has been added in the abstract.
- There are a lot of papers [11-27] that are only cited in the introduction, but their results are not discussed. Please, avoid to cite some works without a proper discussion. These papers should be discussed or omitted from the paper.
Answer: Thanks for your valuable suggestion. We have checked these citations in our manuscript, and rewrote the text in this paragraph.
- Figure 4. What about the experimental data? The authors present a validation of the model with some experimental data, but there is no any reference of the experimental data. Are they from a previous work?, are the results published in any other paper? If there are experimental results obtained by the authors, they should describe the experimental facility and how the experimental data were obtained!.
Answer: Sorry, we did not make it clear. Here we used the experimental data from our laboratory, and these experimental result has been published in the Journal and thesis. The corresponding rib structure and operating parameters are identical with our simulation model. In our revised papers, the corresponding citations have been added in Fig. 4 as a reference.
- In most of the figure, the authors introduce the variable H in the horizontal axis. Is it equivalent to the length of the tube?, why not introduce the length?
Answer: That is a good question. For supercritical fluid, a steep variation of thermophysical properties presents, especially in the pseudocritical region. As seen in Figure 4, a remarkable peak of specific heat appeared in the pseudocritical point. Even though a given heat fluxes added on the heating wall, a non-linear temperature increases will be presented. Therefore, in generally, we used enthalpy (H) as a variable, rather than the length of the tube.
- Figure 12. Please, introduce the units in the variables presented in this figure.
Answer: Thanks for your good suggestion. We have corrected this figure, and the units of these variables have been added in Fig.12.
- Figure 12 (c). The authors present the variable η2, which is defined as the ratio between pressure drop and heat transfer. But other authors used the Performance Evaluation Criteria (PEC). See the following references:
- C´orcoles et al. 2020. Numerical and experimental study of the heat transfer process in a double pipe heat exchanger with inner corrugated tubes. International Journal of Thermal Sciences, 158, 106526.
- Wang et al., 2019. Optimal design of a double pipe heat exchanger based on the outward helically corrugated tube. International Journal of Heat and Mass Transfer, 135, 706-716.
Answer: Thanks for your recommended papers. A few scholars adopt several different Performance Evaluation Criteria (PEC) for estimating the performance of heat transfer enhancement.
Actually, our authors ever attempt to adapt different PECs (such as ,,) to evaluate the optimal rib structure. According to the evaluated result of h2 and h3 , we can get the same results, thus in our study, we kept only one PEC result.
Round 2
Reviewer 2 Report
I think that the paper can be published the journal.
