Sustainable Heat Transfer Management: Modeling of Entropy Generation Minimization and Nusselt Number Development in Internal Flows with Various Shapes of Cross-Sections Using Water and Al₂O₃/Water Nanofluid

Round 1

Reviewer 1 Report

I would like to send my review comments for the manuscript entitled " Experimental modeling of entropy generation minimization and Nusselt number development in internal flows with various shapes of cross sections using water and  nanofluid" with manuscript code of water-2112101. In this manuscript, authors have performed an experimental investigation on a variety of cross-sections. They studied the effects of Reynolds number and cross-section on the heat transfer and entropy generation. The nanofluid properties are correctly measured, which is a benefit for this paper. The data is correctly validated using analytical methods, and the results could be used in industries as well. The manuscript seems to cover a wide range of areas, and therefore, I believe that after minor revisions, it can be accepted for publication in the journal of Water.

1. There are rare typo errors in the article that should be corrected.

2. It is recommended to add some suggestions for future research in this area to improve the conclusion.

3. The "Introduction" section should be impressive and informative. Some relative papers are highly recommended to improve this section:

Zhong, Q., Chen, Y., Zhu, B., Liao, S., & Shi, K. (2022). A temperature field reconstruction method based on acoustic thermometry. Measurement, 200, 111642. doi: https://doi.org/10.1016/j.measurement.2022.111642

Cui, W., Li, X., Li, X., Si, T., Lu, L., Ma, T.,... Wang, Q. (2022). Thermal performance of modified melamine foam/graphene/paraffin wax composite phase change materials for solar-thermal energy conversion and storage. Journal of Cleaner Production, 367, 133031. doi: https://doi.org/10.1016/j.jclepro.2022.133031

Aicha G., Noureddine E., Djamel G., Ahmed H., Abdel Halim K.S., Muhammad I. K. (2022). Electrocoagulation process for removing dyes and chemical oxygen demand from wastewater: operational conditions and economic assessment - a review, Desalination and Water treatment, 271, 74-107. doi: https://doi.org/10.5004/dwt.2022.28792

Cui, W., Si, T., Li, X., Li, X., Lu, L., Ma, T.,... Wang, Q. (2022). Heat transfer analysis of phase change material composited with metal foam-fin hybrid structure in inclination container by numerical simulation and artificial neural network. Energy Reports, 8, 10203-10218. doi: https://doi.org/10.1016/j.egyr.2022.07.178

Guo, Z., Tian, X., Wu, Z., Yang, J., & Wang, Q. (2022). Heat transfer of granular flow around aligned tube bank in moving bed: Experimental study and theoretical prediction by thermal resistance model. Energy Conversion and Management, 257, 115435. doi: https://doi.org/10.1016/j.enconman.2022.115435 

Qu, M., Liang, T., Hou, J., Liu, Z., Yang, E.,... Liu, X. (2022). Laboratory study and field application of amphiphilic molybdenum disulfide nanosheets for enhanced oil recovery. Journal of Petroleum Science and Engineering, 208, 109695. doi: https://doi.org/10.1016/j.petrol.2021.109695

4. Figure 12 should be explained in more detail.

5. Comparisons with other research should be added to the "Results and discussion" section.

Author Response

Response to reviewer #1
Reviewer's suggestions: I would like to send my review comments for the manuscript entitled " Experimental modeling of entropy generation minimization and Nusselt number development in internal flows with various shapes of cross sections using water and  nanofluid" with manuscript code of water-2112101. In this manuscript, authors have performed an experimental investigation on a variety of cross-sections. They studied the effects of Reynolds number and cross-section on the heat transfer and entropy generation. The nanofluid properties are correctly measured, which is a benefit for this paper. The data is correctly validated using analytical methods, and the results could be used in industries as well. The manuscript seems to cover a wide range of areas, and therefore, I believe that after minor revisions, it can be accepted for publication in the journal of Water.

Comment 1: There are rare typo errors in the article that should be corrected.
Authors' response to comments 1: Thank you for your fruitful comment. The manuscript is checked thoroughly and all the typos are corrected. 

Comment 2: It is recommended to add some suggestions for future research in this area to improve the conclusion.
Authors' response to comments 2: Thank you for your comment. The suggestions are added to the conclusion of the manuscript: 
For further research in this area, other cross-sections such as coils, ducts, and triangular could be considered, and a comparison should be made between circular and other cross sections. Also, recently, the use of machine learning algorithms for predicting parameters is becoming common, so other research could be devoted to proposing predictive models.  

Comment 3: The "Introduction" section should be impressive and informative. Some relative papers are highly recommended to improve this section:
Zhong, Q., Chen, Y., Zhu, B., Liao, S., & Shi, K. (2022). A temperature field reconstruction method based on acoustic thermometry. Measurement, 200, 111642. doi: https://doi.org/10.1016/j.measurement.2022.111642

Cui, W., Li, X., Li, X., Si, T., Lu, L., Ma, T.,... Wang, Q. (2022). Thermal performance of modified melamine foam/graphene/paraffin wax composite phase change materials for solar-thermal energy conversion and storage. Journal of Cleaner Production, 367, 133031. doi: https://doi.org/10.1016/j.jclepro.2022.133031

Aicha G., Noureddine E., Djamel G., Ahmed H., Abdel Halim K.S., Muhammad I. K. (2022). Electrocoagulation process for removing dyes and chemical oxygen demand from wastewater: operational conditions and economic assessment - a review, Desalination and Water treatment, 271, 74-107. doi: https://doi.org/10.5004/dwt.2022.28792

Cui, W., Si, T., Li, X., Li, X., Lu, L., Ma, T.,... Wang, Q. (2022). Heat transfer analysis of phase change material composited with metal foam-fin hybrid structure in inclination container by numerical simulation and artificial neural network. Energy Reports, 8, 10203-10218. doi: https://doi.org/10.1016/j.egyr.2022.07.178

Guo, Z., Tian, X., Wu, Z., Yang, J., & Wang, Q. (2022). Heat transfer of granular flow around aligned tube bank in moving bed: Experimental study and theoretical prediction by thermal resistance model. Energy Conversion and Management, 257, 115435. doi: https://doi.org/10.1016/j.enconman.2022.115435 

Qu, M., Liang, T., Hou, J., Liu, Z., Yang, E.,... Liu, X. (2022). Laboratory study and field application of amphiphilic molybdenum disulfide nanosheets for enhanced oil recovery. Journal of Petroleum Science and Engineering, 208, 109695. doi: https://doi.org/10.1016/j.petrol.2021.109695
Authors' response to comments 3: Thank you for your comment. The introduction is revised, and the mentioned papers are used to make the introduction informative.

Comment 4: Figure 12 should be explained in more detail.
Authors' response to comments 4: Thank you for your comment. The following is added to the description of Figure 12: 
Based on Figure 12d and 12e, the maximum average Nusselt number, which is in circular tubes, have higher value in the concentration of 3% wt. This shows there is an optimum for the addition of nanoparticles to the base fluids. The physical justification of this phenomenon could be explained by the sedimentation of nanoparticles in higher concentrations. Since in higher concentrations more nanoparticles would cluster and lose their potential heat capabilities, the average Nusselt number would decrease after the optimum concentration.

Comment 5: Comparisons with other research should be added to the "Results and discussion" section.
Authors' response to comments 5: Thank you for your wise comment. The comparisons are added to the manuscript. 

Response to reviewer #2
Reviewer's suggestions: The subject of the MS is interesting and is publishable after some corrections:

Comment 1: For the high nanoparticle concentration (4%), is there any sedimentation? In the text it is mentioned that “However, partial deposition of ?? - ????2??3 nanoparticles, including a 2.5 percent volume component in water, were seen during the test (4-5 hours)”   but it is not explained about 4 %.
Authors' response to comments 1: Thank you for your kind comment. The 2.5% was a typo, and actually, the 4% wt nanofluid is partially deposited. The mistake is corrected per your kind comment. 

Comment 2: How did the authors conclude that the flow is fully developed? Please explain in the text, why the length of the tube is enough to achieve the fully developed flow.
Authors' response to comments 2: Thank you for your comment. Since the tube length is 2700 mm, the first part of the flow (1160 mm) is without the heat flux, and this is to ensure that the flow is hydrodynamically fully developed. Moreover, as can be seen from Figure 2, the flow from the X/D=20 is thermally fully developed as well. 

Comment 3: In the introduction section there some related papers which can be addressed:
https://doi.org/10.1016/j.icheatmasstransfer.2022.106098
10.1016/j.applthermaleng.2018.09.11 
Authors' response to comments 3: Thank you for your comment. The mentioned papers are added to the introduction as follows: 
Delouei et al. [17] studied the thermal effects of multi-walled carbon nanotubes (MWCNT) on a vibrating heat exchanger. They concluded that by using MWCNT under vibration the heat transfer coefficient would increase by 80.52%. In another study, Delouei et al. [18] studied the effects of nanoparticles on pressure drop and heat transfer coefficient of a turbulent flow. They reported that by utilizing ultrasonic vibration the negative effects of pressure drop was reduced, and the heat transfer coefficient was improved.

Response to reviewer #3
Reviewer's suggestions: This paper carries out an experimental study on the impact of cross section and presence of nano particles on the heat transfer and entropy generation in the pipe flow. It has clear application for in various thermal settings. Uncertainty quantification is performed, which adds to the value of the paper. The experimental results are calibrated by comparing them with famous Shah and London data. The paper is well-written and conclusions are clear. I only have few comments to improve the quality of the paper.
 
Comment 1: The impact of nanfluids on heat transfer is demonstrated in experiments, but not enough analysis is carried out to add insight on why such improvement is observed. For example, the impact of clustering of nanoparticles and surfactants are not discussed. Also, it is known that by time, the positive impact of nanoparticles re reduced as more fractals are formed, which adds to the clustering. More discussion is needed in this regard. 
Authors' response to comments 1: Thank you for your kind comment. The following is added to the manuscript per your wise comment: 
The addition of nanoparticles would ameliorate the thermal performance of the base fluid in in two main ways. First, since the nanoparticles are mainly metallic, they have high thermal conductivity. Therefore, adding these nanoparticles would help the thermal properties of the base fluid. Moreover, by adding nanoparticles, the wettability of the fluid would increase, so higher amounts of heat could be dissipated from the surface using the nanofluid. 
However, nanofluid stability is another factor that needs to be considered. Surfactant is used to increase the stability of nanofluid and avoid the nanoparticles from being clustered. This clustering could reduce the thermal performance of the fluid through two mechanisms. The first is that the nanofluid loses the increased thermal properties and the wettability decreases. Also, they cause thermal resistance that could decrease the Nusselt number and increase the entropy generation. 

Author Response File: Author Response.docx

Reviewer 2 Report

The subject of the MS is interesting and is publishable after some corrections:

For the high nanoparticle concentration (4%), is there any sedimentation? In the text it is mentioned that “However, partial deposition of ? − ??2?3 nanoparticles, including a 2.5 percent volume component in water, were seen during the test (4-5 hours)”   but it is not explained about 4 %.

How did the authors conclude that the flow is fully developed? Please explain in the text, why the length of the tube is enough to achieve the fully developed flow.

In the introduction section there some related papers which can be addressed:

https://doi.org/10.1016/j.icheatmasstransfer.2022.106098

10.1016/j.applthermaleng.2018.09.113

Author Response

Response to reviewer #1
Reviewer's suggestions: I would like to send my review comments for the manuscript entitled " Experimental modeling of entropy generation minimization and Nusselt number development in internal flows with various shapes of cross sections using water and  nanofluid" with manuscript code of water-2112101. In this manuscript, authors have performed an experimental investigation on a variety of cross-sections. They studied the effects of Reynolds number and cross-section on the heat transfer and entropy generation. The nanofluid properties are correctly measured, which is a benefit for this paper. The data is correctly validated using analytical methods, and the results could be used in industries as well. The manuscript seems to cover a wide range of areas, and therefore, I believe that after minor revisions, it can be accepted for publication in the journal of Water.

Comment 1: There are rare typo errors in the article that should be corrected.
Authors' response to comments 1: Thank you for your fruitful comment. The manuscript is checked thoroughly and all the typos are corrected. 

Comment 2: It is recommended to add some suggestions for future research in this area to improve the conclusion.
Authors' response to comments 2: Thank you for your comment. The suggestions are added to the conclusion of the manuscript: 
For further research in this area, other cross-sections such as coils, ducts, and triangular could be considered, and a comparison should be made between circular and other cross sections. Also, recently, the use of machine learning algorithms for predicting parameters is becoming common, so other research could be devoted to proposing predictive models.  

Comment 3: The "Introduction" section should be impressive and informative. Some relative papers are highly recommended to improve this section:
Zhong, Q., Chen, Y., Zhu, B., Liao, S., & Shi, K. (2022). A temperature field reconstruction method based on acoustic thermometry. Measurement, 200, 111642. doi: https://doi.org/10.1016/j.measurement.2022.111642

Cui, W., Li, X., Li, X., Si, T., Lu, L., Ma, T.,... Wang, Q. (2022). Thermal performance of modified melamine foam/graphene/paraffin wax composite phase change materials for solar-thermal energy conversion and storage. Journal of Cleaner Production, 367, 133031. doi: https://doi.org/10.1016/j.jclepro.2022.133031

Aicha G., Noureddine E., Djamel G., Ahmed H., Abdel Halim K.S., Muhammad I. K. (2022). Electrocoagulation process for removing dyes and chemical oxygen demand from wastewater: operational conditions and economic assessment - a review, Desalination and Water treatment, 271, 74-107. doi: https://doi.org/10.5004/dwt.2022.28792

Cui, W., Si, T., Li, X., Li, X., Lu, L., Ma, T.,... Wang, Q. (2022). Heat transfer analysis of phase change material composited with metal foam-fin hybrid structure in inclination container by numerical simulation and artificial neural network. Energy Reports, 8, 10203-10218. doi: https://doi.org/10.1016/j.egyr.2022.07.178

Guo, Z., Tian, X., Wu, Z., Yang, J., & Wang, Q. (2022). Heat transfer of granular flow around aligned tube bank in moving bed: Experimental study and theoretical prediction by thermal resistance model. Energy Conversion and Management, 257, 115435. doi: https://doi.org/10.1016/j.enconman.2022.115435 

Qu, M., Liang, T., Hou, J., Liu, Z., Yang, E.,... Liu, X. (2022). Laboratory study and field application of amphiphilic molybdenum disulfide nanosheets for enhanced oil recovery. Journal of Petroleum Science and Engineering, 208, 109695. doi: https://doi.org/10.1016/j.petrol.2021.109695
Authors' response to comments 3: Thank you for your comment. The introduction is revised, and the mentioned papers are used to make the introduction informative.

Comment 4: Figure 12 should be explained in more detail.
Authors' response to comments 4: Thank you for your comment. The following is added to the description of Figure 12: 
Based on Figure 12d and 12e, the maximum average Nusselt number, which is in circular tubes, have higher value in the concentration of 3% wt. This shows there is an optimum for the addition of nanoparticles to the base fluids. The physical justification of this phenomenon could be explained by the sedimentation of nanoparticles in higher concentrations. Since in higher concentrations more nanoparticles would cluster and lose their potential heat capabilities, the average Nusselt number would decrease after the optimum concentration.

Comment 5: Comparisons with other research should be added to the "Results and discussion" section.
Authors' response to comments 5: Thank you for your wise comment. The comparisons are added to the manuscript. 

Response to reviewer #2
Reviewer's suggestions: The subject of the MS is interesting and is publishable after some corrections:

Comment 1: For the high nanoparticle concentration (4%), is there any sedimentation? In the text it is mentioned that “However, partial deposition of ?? - ????2??3 nanoparticles, including a 2.5 percent volume component in water, were seen during the test (4-5 hours)”   but it is not explained about 4 %.
Authors' response to comments 1: Thank you for your kind comment. The 2.5% was a typo, and actually, the 4% wt nanofluid is partially deposited. The mistake is corrected per your kind comment. 

Comment 2: How did the authors conclude that the flow is fully developed? Please explain in the text, why the length of the tube is enough to achieve the fully developed flow.
Authors' response to comments 2: Thank you for your comment. Since the tube length is 2700 mm, the first part of the flow (1160 mm) is without the heat flux, and this is to ensure that the flow is hydrodynamically fully developed. Moreover, as can be seen from Figure 2, the flow from the X/D=20 is thermally fully developed as well. 

Comment 3: In the introduction section there some related papers which can be addressed:
https://doi.org/10.1016/j.icheatmasstransfer.2022.106098
10.1016/j.applthermaleng.2018.09.11 
Authors' response to comments 3: Thank you for your comment. The mentioned papers are added to the introduction as follows: 
Delouei et al. [17] studied the thermal effects of multi-walled carbon nanotubes (MWCNT) on a vibrating heat exchanger. They concluded that by using MWCNT under vibration the heat transfer coefficient would increase by 80.52%. In another study, Delouei et al. [18] studied the effects of nanoparticles on pressure drop and heat transfer coefficient of a turbulent flow. They reported that by utilizing ultrasonic vibration the negative effects of pressure drop was reduced, and the heat transfer coefficient was improved.

Response to reviewer #3
Reviewer's suggestions: This paper carries out an experimental study on the impact of cross section and presence of nano particles on the heat transfer and entropy generation in the pipe flow. It has clear application for in various thermal settings. Uncertainty quantification is performed, which adds to the value of the paper. The experimental results are calibrated by comparing them with famous Shah and London data. The paper is well-written and conclusions are clear. I only have few comments to improve the quality of the paper.
 
Comment 1: The impact of nanfluids on heat transfer is demonstrated in experiments, but not enough analysis is carried out to add insight on why such improvement is observed. For example, the impact of clustering of nanoparticles and surfactants are not discussed. Also, it is known that by time, the positive impact of nanoparticles re reduced as more fractals are formed, which adds to the clustering. More discussion is needed in this regard. 
Authors' response to comments 1: Thank you for your kind comment. The following is added to the manuscript per your wise comment: 
The addition of nanoparticles would ameliorate the thermal performance of the base fluid in in two main ways. First, since the nanoparticles are mainly metallic, they have high thermal conductivity. Therefore, adding these nanoparticles would help the thermal properties of the base fluid. Moreover, by adding nanoparticles, the wettability of the fluid would increase, so higher amounts of heat could be dissipated from the surface using the nanofluid. 
However, nanofluid stability is another factor that needs to be considered. Surfactant is used to increase the stability of nanofluid and avoid the nanoparticles from being clustered. This clustering could reduce the thermal performance of the fluid through two mechanisms. The first is that the nanofluid loses the increased thermal properties and the wettability decreases. Also, they cause thermal resistance that could decrease the Nusselt number and increase the entropy generation. 

Author Response File: Author Response.docx

Reviewer 3 Report

This paper carries out an experimental study on the impact of cross section and presence of nano particles on the heat transfer and entropy generation in the pipe flow. It has clear application for in various thermal settings. Uncertainty quantification is performed, which adds to the value of the paper. The experimental results are calibrated by comparing them with famous Shah and London data. The paper is well-written and conclusions are clear. 

I only have few comments to improve the quality of the paper. The impact of nanfluids on heat transfer is demonstrated in experiments, but not enough analysis is carried out to add insight on why such improvement is observed. For example, the impact of clustering of nanoparticles and surfactants are not discussed. Also, it is known that by time, the positive impact of nanoparticles re reduced as more fractals are formed, which adds to the clustering. More discussion is needed in this regard. 

Author Response

Response to reviewer #1
Reviewer's suggestions: I would like to send my review comments for the manuscript entitled " Experimental modeling of entropy generation minimization and Nusselt number development in internal flows with various shapes of cross sections using water and  nanofluid" with manuscript code of water-2112101. In this manuscript, authors have performed an experimental investigation on a variety of cross-sections. They studied the effects of Reynolds number and cross-section on the heat transfer and entropy generation. The nanofluid properties are correctly measured, which is a benefit for this paper. The data is correctly validated using analytical methods, and the results could be used in industries as well. The manuscript seems to cover a wide range of areas, and therefore, I believe that after minor revisions, it can be accepted for publication in the journal of Water.

Comment 1: There are rare typo errors in the article that should be corrected.
Authors' response to comments 1: Thank you for your fruitful comment. The manuscript is checked thoroughly and all the typos are corrected. 

Comment 2: It is recommended to add some suggestions for future research in this area to improve the conclusion.
Authors' response to comments 2: Thank you for your comment. The suggestions are added to the conclusion of the manuscript: 
For further research in this area, other cross-sections such as coils, ducts, and triangular could be considered, and a comparison should be made between circular and other cross sections. Also, recently, the use of machine learning algorithms for predicting parameters is becoming common, so other research could be devoted to proposing predictive models.  

Comment 3: The "Introduction" section should be impressive and informative. Some relative papers are highly recommended to improve this section:
Zhong, Q., Chen, Y., Zhu, B., Liao, S., & Shi, K. (2022). A temperature field reconstruction method based on acoustic thermometry. Measurement, 200, 111642. doi: https://doi.org/10.1016/j.measurement.2022.111642

Cui, W., Li, X., Li, X., Si, T., Lu, L., Ma, T.,... Wang, Q. (2022). Thermal performance of modified melamine foam/graphene/paraffin wax composite phase change materials for solar-thermal energy conversion and storage. Journal of Cleaner Production, 367, 133031. doi: https://doi.org/10.1016/j.jclepro.2022.133031

Aicha G., Noureddine E., Djamel G., Ahmed H., Abdel Halim K.S., Muhammad I. K. (2022). Electrocoagulation process for removing dyes and chemical oxygen demand from wastewater: operational conditions and economic assessment - a review, Desalination and Water treatment, 271, 74-107. doi: https://doi.org/10.5004/dwt.2022.28792

Cui, W., Si, T., Li, X., Li, X., Lu, L., Ma, T.,... Wang, Q. (2022). Heat transfer analysis of phase change material composited with metal foam-fin hybrid structure in inclination container by numerical simulation and artificial neural network. Energy Reports, 8, 10203-10218. doi: https://doi.org/10.1016/j.egyr.2022.07.178

Guo, Z., Tian, X., Wu, Z., Yang, J., & Wang, Q. (2022). Heat transfer of granular flow around aligned tube bank in moving bed: Experimental study and theoretical prediction by thermal resistance model. Energy Conversion and Management, 257, 115435. doi: https://doi.org/10.1016/j.enconman.2022.115435 

Qu, M., Liang, T., Hou, J., Liu, Z., Yang, E.,... Liu, X. (2022). Laboratory study and field application of amphiphilic molybdenum disulfide nanosheets for enhanced oil recovery. Journal of Petroleum Science and Engineering, 208, 109695. doi: https://doi.org/10.1016/j.petrol.2021.109695
Authors' response to comments 3: Thank you for your comment. The introduction is revised, and the mentioned papers are used to make the introduction informative.

Comment 4: Figure 12 should be explained in more detail.
Authors' response to comments 4: Thank you for your comment. The following is added to the description of Figure 12: 
Based on Figure 12d and 12e, the maximum average Nusselt number, which is in circular tubes, have higher value in the concentration of 3% wt. This shows there is an optimum for the addition of nanoparticles to the base fluids. The physical justification of this phenomenon could be explained by the sedimentation of nanoparticles in higher concentrations. Since in higher concentrations more nanoparticles would cluster and lose their potential heat capabilities, the average Nusselt number would decrease after the optimum concentration.

Comment 5: Comparisons with other research should be added to the "Results and discussion" section.
Authors' response to comments 5: Thank you for your wise comment. The comparisons are added to the manuscript. 

Response to reviewer #2
Reviewer's suggestions: The subject of the MS is interesting and is publishable after some corrections:

Comment 1: For the high nanoparticle concentration (4%), is there any sedimentation? In the text it is mentioned that “However, partial deposition of ?? - ????2??3 nanoparticles, including a 2.5 percent volume component in water, were seen during the test (4-5 hours)”   but it is not explained about 4 %.
Authors' response to comments 1: Thank you for your kind comment. The 2.5% was a typo, and actually, the 4% wt nanofluid is partially deposited. The mistake is corrected per your kind comment. 

Comment 2: How did the authors conclude that the flow is fully developed? Please explain in the text, why the length of the tube is enough to achieve the fully developed flow.
Authors' response to comments 2: Thank you for your comment. Since the tube length is 2700 mm, the first part of the flow (1160 mm) is without the heat flux, and this is to ensure that the flow is hydrodynamically fully developed. Moreover, as can be seen from Figure 2, the flow from the X/D=20 is thermally fully developed as well. 

Comment 3: In the introduction section there some related papers which can be addressed:
https://doi.org/10.1016/j.icheatmasstransfer.2022.106098
10.1016/j.applthermaleng.2018.09.11 
Authors' response to comments 3: Thank you for your comment. The mentioned papers are added to the introduction as follows: 
Delouei et al. [17] studied the thermal effects of multi-walled carbon nanotubes (MWCNT) on a vibrating heat exchanger. They concluded that by using MWCNT under vibration the heat transfer coefficient would increase by 80.52%. In another study, Delouei et al. [18] studied the effects of nanoparticles on pressure drop and heat transfer coefficient of a turbulent flow. They reported that by utilizing ultrasonic vibration the negative effects of pressure drop was reduced, and the heat transfer coefficient was improved.

Response to reviewer #3
Reviewer's suggestions: This paper carries out an experimental study on the impact of cross section and presence of nano particles on the heat transfer and entropy generation in the pipe flow. It has clear application for in various thermal settings. Uncertainty quantification is performed, which adds to the value of the paper. The experimental results are calibrated by comparing them with famous Shah and London data. The paper is well-written and conclusions are clear. I only have few comments to improve the quality of the paper.
 
Comment 1: The impact of nanfluids on heat transfer is demonstrated in experiments, but not enough analysis is carried out to add insight on why such improvement is observed. For example, the impact of clustering of nanoparticles and surfactants are not discussed. Also, it is known that by time, the positive impact of nanoparticles re reduced as more fractals are formed, which adds to the clustering. More discussion is needed in this regard. 
Authors' response to comments 1: Thank you for your kind comment. The following is added to the manuscript per your wise comment: 
The addition of nanoparticles would ameliorate the thermal performance of the base fluid in in two main ways. First, since the nanoparticles are mainly metallic, they have high thermal conductivity. Therefore, adding these nanoparticles would help the thermal properties of the base fluid. Moreover, by adding nanoparticles, the wettability of the fluid would increase, so higher amounts of heat could be dissipated from the surface using the nanofluid. 
However, nanofluid stability is another factor that needs to be considered. Surfactant is used to increase the stability of nanofluid and avoid the nanoparticles from being clustered. This clustering could reduce the thermal performance of the fluid through two mechanisms. The first is that the nanofluid loses the increased thermal properties and the wettability decreases. Also, they cause thermal resistance that could decrease the Nusselt number and increase the entropy generation. 

Author Response File: Author Response.docx