Round 1

Reviewer 1 Report

Please see attachment.

Comments for author File: Comments.pdf

Author Response

Authors’ Response to the Review Comments

 

Journal: Sustainability2023

Manuscript ID: sustainability-2127542

Title of Paper: Improving the heat transfer of phase change composites for thermal energy storage by adding copper: preparation and thermal properties.

Authors: Abdelwaheb TRIGUI, Makki ABDELMOULEH.

 

Date Sent: 22 December 2022

 

We appreciate the time and efforts by the editor and referees in reviewing this manuscript. We would like to thank the reviewers for the careful and thorough reading of this manuscript and for the insightful comments and constructive suggestions, which helped in improving the manuscript. We have addressed all issues indicated in the review report point by point, and we hope our revision would improve the quality of the paper to meet the level of their satisfaction.

Any revisions made to the manuscript are :

• marked up using the “Track Changes” function
• highlighted with a cyan background.

 

Response to Comments from Reviewer #1:

Reviewer #1:

In this manuscript, the author presented the synthetization of a phase change composites (PCC) consisting of organic phase change material (PCM) and Cu nanoparticle additives and thoroughly characterized the performances of heat transfer and shape stability of samples with various Cu compositions. The manuscript is well written and the results seem interesting and fit the standard of the journal publication. The reviewer would like to pass the following comments to the authors and once they have been addressed, the manuscript can be considered acceptance.

1. The reviewer would like to encourage the authors to be clearer about the range of temperature they meant for the solar energy storage application (e.g., solar thermophotovoltaic, etc) mentioned in the manuscript. Depending on which applications are the targets, the temperature may be higher than the temperature below which the current PCC is thermally stable.

As suggested, further discussions have been added on the conclusion.

 

2. The reviewer suggests the authors to further emphasize of advantage of choosing Cu as the additive over other candidates having even higher thermal conductivities (e.g., graphite, graphene, CNT, hBN, silver, etc). It is intuitive that the composite thermal conductivity can be much enhanced by adding high-thermal-conductivity materials, but the authors chose Cu and the reasons could be explained more.

There are various types of nanoparticles being used as enhancers for PCMs including carbon-based nanoparticles such as multi-walled carbon nanotubes (MWCNTs), carbon nanofibers (CNFs), carbon nanowires (CNWs), graphene nanoplatelets (GNPs), graphite and metal and metallic oxide nanoparticles like Copper (Cu), Silver (Ag), Gold (Au), Aluminum Oxide (Al2O3) and Copper Oxide (CuO). For this study, Copper was chosen tube due to its exceptionally high thermal conductivity, low cost, and availability.

Metal and metal-oxide nanoparticles have been widely investigated for fabricating thermally conductive PCCs owing to their robust mechanical properties, high thermal conductivity and excellent chemical stability. Wu et al. [1] investigated the enhancement in heat transfer efficiency due to the infiltration of Al, Cu, and C/Cu nanoparticles (25 nm) into PW. The Cu-based PCCs possessed superior heat transfer performance compared with those of other PCCs. Moreover, the presence of Cu nanoparticles significantly increased the charging/discharging rates of the PCCs, where the charging/discharging times of the Cu-based PCCs (1 wt%) were reduced by 30.3% and 28.2%, respectively.

In contrast to metal-based and carbon-based additives, ceramic- based materials such as BN, AlN, SiO2, and clay mineral-based materials not only exhibit considerable thermal conductivities but are also electrically insulating, which enables the fabrication of high-performance form-stable PCCs for the thermal management of electronic devices [2].

[1] S. Wu , D. Zhu , X. Zhang , J. Huang , Preparation and melting/freezing characteristics of Cu/paraffin nanofluid as phase-change material (PCM), Energy Fuels 24 (2010) 1894–1898

[2] J. Yang , L.S. Tang , L. Bai , R.Y. Bao , Z.Y. Liu , B.H. Xie , M.B. Yang , W. Yang , High- -performance composite phase change materials for energy conversion based on macroscopically three-dimensional structural materials, Mater. Horiz. 6 (2019) 250–273.

 

3. When performing the thermography of the sample, the emissivity of the sample is needed. The reviewer wonders if the emissivity of the samples were measured or assumed, and what were the emissivity values? This info should be properly included in the manuscript.

As suggested, more detail have been added in the revised manuscript.

 

4. In Figure 3, even though the authors have described the images in detail, the reviewer still found difficulty of differentiating paraffin, LDPE, and Cu nanoparticles. Is it possible to label each material in one of the SEM images so that they can be better understood?

More detail on the morphological part and the role of Cu in the morphological stability of the final material has been presented in the revised manuscript.

 

5. It is interesting in Figure 5 that the max mass loss temperature can be delayed until higher temperature by adding more Cu into the composites. Based on the trend, may we say it would be beneficial to go beyond 15% in terms of Cu weight such that the composites may be applied to higher temperature applications?

Based on previous work and bibliographic studies, the use of metallic microparticles more than 15% in composite materials can lead to the formation of agglomerates which have a negative effect on the homogeneity of the materials and subsequently on their final properties.

 

6. In the leakage tests, the authors applied 16 heating cycles. The reviewer is curious about how many cycles should one expects in practical applications. In other words, the leak rate of the samples, for example PCC6 with a value of 5.5%, would this value stay unchanged even more heating cycles are applied? In addition, in Figure 8, it seems that the cycles were applied over a long period of time, the reviewer also wonders how each cycle was applied, was it still 10 C/min as stated earlier in the manuscript? If not, did the heating occur gradually or rapidly?

Shape stabilized PCM (SSPCM) is one of the methods currently being used for encapsulating PCMs to solve the problems of leakage and volatilization. Qin et al. [3] found significant leakage of Paraffin-HDPE SSPCMs when the mass fraction of HDPE reduced to lower than 10wt.%. Summarized from the literature, the lowest mass fraction of HDPE needed in paraffin-HDPE composites could be suggested as 23wt.% [3], 24wt.% [4] and 25wt.% [5] without any paraffin seepage when melted. During the test, all samples were exposed directly to the environment to weigh without any encapsulation. Firstly, the samples were weighed and marked the mass as M0. Then, they were placed on the filter papers and put in a vacuum oven with a temperature of 50 °C. After an hour, the samples were taken out and weighed as M1. Such steps were repeated by n times and the mass of samples was recorded as Mn. For each component, three samples were prepared and measured, and an average value was taken to calculate the leakage rate of the SSPCM samples. The leak rate can be calculated as follows from equation (1).

[3] P.H. Qin, R. Yang, Y.P. Zhang, K.P. Lin. Thermal properties of shape stabilized phase change materials. Journal of Tsinghua University (Natural Science Edition) 43 (6) (2003) 833-835.

[4] K. Kaygusuz, A. Sarı. High density polyethylene/paraffin composites as form-stable phase change material for thermal energy storage. Energy Sources 29 (3) (2007) 261-270.

[5] H. Ye, X.S. Ge. Preparation of polyethylene-paraffin compound as a form-stable solid-liquid phase change material. Solar Energy Materials and Solar Cells 64 (1) (2000) 37-44.

 

7. Minor suggestions:
8. Figure 2 could use a higher resolution.

The proposed change in the quality of figures was carried out on the revised manuscript

1. Font size from line 201 to line 215 seems smaller than the rest of the manuscript.

The proposed change in font size was carried out on the revised manuscript

1. In line 297, there is no should be removed. There should then be there. d. In Figure 5, the legends for PCC5 and PCC6 look too similar, it would be helpful to make them more different (such as using dashed line, etc).

It’s ok,

 

1. In line 310, after at elevated temperature, the redundant period should be deleted.

It’s ok,

 

1. The subscripts in CP, Tpm, and Tps should be properly written, the reviewer suggests the author thoroughly check the manuscript for these issues.

Ok, we have checked the manuscript for these issues

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript by Trigui et al. examines copper-additive phase change composites (PCCs) as a potential solution to the limitations of traditional phase change materials (PCMs) for energy conservation. The authors prepared six PCCs with varying concentrations of SEBS, LDPE, and copper and conducted various tests to assess their characteristics. The results indicate that PCCs have high latent heat storage capacity, low supercooling, high thermal conductivities, and fast response times, addressing common problems with PCMs. The content of the manuscript is relevant to the journal Sustainability and the findings may be of interest to its readers. However, before it can be considered for publication, the authors should address the following comments:

1. The introduction of PCCs (lines 78-119) should be restructured to provide a clearer overview of the drawbacks of PCMs, the definition of PCCs, and the advantages of PCCs according to the literature.

 

2. In the TGA analysis conducted under Nitrogen flow, the results show that the addition of Cu increases the decomposition onset temperature and the maximum weight loss temperature, indicating an improvement in the thermal stability of the composite. However, it is important to consider whether the oxidation of copper particles in the air could affect the conclusion about the thermal stability of PCCs. The authors should address this in the manuscript.

Author Response

Authors’ Response to the Review Comments

 

Journal: Sustainability2023

Manuscript ID: sustainability-2127542

Title of Paper: Improving the heat transfer of phase change composites for thermal energy storage by adding copper: preparation and thermal properties.

Authors: Abdelwaheb TRIGUI, Makki ABDELMOULEH.

 

Date Sent: 22 December 2022

 

We appreciate the time and efforts by the editor and referees in reviewing this manuscript. We would like to thank the reviewers for the careful and thorough reading of this manuscript and for the insightful comments and constructive suggestions, which helped in improving the manuscript. We have addressed all issues indicated in the review report point by point, and we hope our revision would improve the quality of the paper to meet the level of their satisfaction.

Any revisions made to the manuscript are :

• marked up using the “Track Changes” function
• highlighted with a cyan background.

 

Response to Comments from Reviewer #2:

 

Reviewer #2:

The manuscript by Trigui et al. examines copper-additive phase change composites (PCCs) as a potential solution to the limitations of traditional phase change materials (PCMs) for energy conservation. The authors prepared six PCCs with varying concentrations of SEBS, LDPE, and copper and conducted various tests to assess their characteristics. The results indicate that PCCs have high latent heat storage capacity, low supercooling, high thermal conductivities, and fast response times, addressing common problems with PCMs. The content of the manuscript is relevant to the journal Sustainability and the findings may be of interest to its readers. However, before it can be considered for publication, the authors should address the following

 

1. The introduction of PCCs (lines 78-119) should be restructured to provide a clearer overview of the drawbacks of PCMs, the definition of PCCs, and the advantages of PCCs according to the literature.

Ok, we have performed the suggested changes to the introduction

 

2. In the TGA analysis conducted under Nitrogen flow, the results show that the addition of Cu increases the decomposition onset temperature and the maximum weight loss temperature, indicating an improvement in the thermal stability of the composite. However, it is important to consider whether the oxidation of copper particles in the air could affect the conclusion about the thermal stability of PCCs. The authors should address this in the manuscript.

The oxidation of the Cu microparticles can take place at a temperature above 500°C (in TGA analysis under oxygen flow ) where the organic material (PCM, SEBS and LDPE) is completely degraded.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

In this manuscript, copper particles were added into the phase change composites to form phase change composites (PCC), which improved the thermal conductivity of hexadecane. The author has characterized the micro morphology, chemical structure, thermal degradation stability and energy storage performance of composite materials, which is of great significance for sustainable energy conservation strategy. Although the author has done a lot of work, the following modifications are required before it is considered for publication.

1、   The manuscript is marked with Figure 2 The serial number of preparation steps of PCCs is wrong. The author is requested to make a modification.

2、   In 3.3. Thermal Stability Analysis of PCCs, the author mentioned that from the DTG curves (Fig. 5 (b)), it can be seen that the addition of Cu increased the decomposition on temperature and the maximum weight loss temperature The marking in Fig. 5 (b) is incorrect, and it is recommended to modify.

3、   In 3.4. The shape stability of PCCs, the author analyzed the relationship between leakage rate and time. What is the author's method for characterizing and calculating the overall leakage rates? The author should give a brief description of this.

4、   In Section 3.6, the author proposes that adding Cu to PCM improves the response time of TES to requirements. However, the author's explanation of the reason is incomprehensible and suggests modification and improvement.

5、   In this manuscript, the phase change composites with 5%, 10% and 15% Cu particles were tested, but the overall effect of the content on the material properties was not clearly stated in the analysis and conclusion. It is suggested that this should be supplemented in the conclusion.

6、   The manuscript lacks the annotation of formula (1), and it is suggested to supplement.

Author Response

Authors’ Response to the Review Comments

 

Journal: Sustainability2023

Manuscript ID: sustainability-2127542

Title of Paper: Improving the heat transfer of phase change composites for thermal energy storage by adding copper: preparation and thermal properties.

Authors: Abdelwaheb TRIGUI, Makki ABDELMOULEH.

 

Date Sent: 22 December 2022

 

We appreciate the time and efforts by the editor and referees in reviewing this manuscript. We would like to thank the reviewers for the careful and thorough reading of this manuscript and for the insightful comments and constructive suggestions, which helped in improving the manuscript. We have addressed all issues indicated in the review report point by point, and we hope our revision would improve the quality of the paper to meet the level of their satisfaction.

Any revisions made to the manuscript are :

• marked up using the “Track Changes” function
• highlighted with a cyan background.

 

Response to Comments from Reviewer #3:

 

 

Reviewer #3:

In this manuscript, copper particles were added into the phase change composites to form phase change composites (PCC), which improved the thermal conductivity of hexadecane. The author has characterized the micro morphology, chemical structure, thermal degradation stability and energy storage performance of composite materials, which is of great significance for sustainable energy conservation strategy. Although the author has done a lot of work, the following modifications are required before it is considered for publication.

 

1、 The manuscript is marked with Figure 2 The serial number of preparation steps of PCCs is wrong. The author is requested to make a modification.

The proposed change in marked of figure 2 was carried out on the revised manuscript.

 

2、 In 3.3. Thermal Stability Analysis of PCCs, the author mentioned that from the DTG curves (Fig. 5 (b)), it can be seen that the addition of Cu increased the decomposition on temperature and the maximum weight loss temperature The marking in Fig. 5 (b) is incorrect, and it is recommended to modify.

Perfect, The TGA part has been revised taking into account the remarks mentioned.

 

3、 In 3.4. The shape stability of PCCs, the author analyzed the relationship between leakage rate and time. What is the author's method for characterizing and calculating the overall leakage rates? The author should give a brief description of this.

As suggested, further discussions have been added on the revised manuscript.

 

4、 In Section 3.6, the author proposes that adding Cu to PCM improves the response time of TES to requirements. However, the author's explanation of the reason is incomprehensible and suggests modification and improvement.

Ok, suggested explanations have been integrated into the text.

 

5、 In this manuscript, the phase change composites with 5%, 10% and 15% Cu particles were tested, but the overall effect of the content on the material properties was not clearly stated in the analysis and conclusion. It is suggested that this should be supplemented in the conclusion.

As suggested, the analysis of the results is carried out in the conclusion.

 

6、 The manuscript lacks the annotation of formula (1), and it is suggested to supplement.

Ok, the annotation of formula (1) is added in the text.

 

Author Response File: Author Response.pdf