Highly Improved Dielectric and Thermal Performance of Polyalphaolefin Oil-Based Fluids Using MgO Nanoparticles

Round 1

Reviewer 1 Report

Dear authors, see the pdf enclosed.

Comments for author File: Comments.pdf

Dear authors, see Point 5 of the pdf enclosed.

Author Response

Dear Reviewer,

Thank you very much for the review of our manuscript. We sincerely appreciate all the valuable comments and suggestions that reviewers gave us. Relying on those insightful comments and suggestions helps us to improve our article in the current version. We carefully considered all comments, made the appropriate changes, and included them in the manuscript. In addition, we also add explanations suggested by reviewers. We hope that after the revised manuscript you find our manuscript suitable for publication and look forward to hearing from you in due course. Authors always welcome constructive comments if any. All modifications in the manuscript have been highlighted in red.

Point 1: Lines 94-95, page 3: it would be better to specify each one of the components listed (e.g., what exactly was used as a thickener, antioxidant, anti-corrosion, and anti-foam additives, etc. – are they from those listed in lines 78-79 of page 2? If so, it would be better to detail them now).

Response:

Thank you for the suggestion. We would like to clarify as follows: The thickener used is PIB, the antioxidant is Butylated hydroxytoluene (BHT), the corrosion inhibitor is a mixture of Barium sulfonate and Benzotriazole, and the anti-foaming agent is HiTEC 2030 (Afton chemical, USA). These details have been added in the revised draft from line 93 to 97 on page 3.

Point 2: Figure 2: Red underlining should be removed from “rmp”.

Response:

Thank you for the suggestion. We have removed the red underline in Figure 2.

Point 3: Lines 123-124, page 4: “... the dielectric properties of PAO oil first increase and then decrease” — is there a proper theoretical explanation of this effect? If so, for the convenience of readers it would be better to include it

Response:

Thank you for the question. The breakdown voltage of PAO/MgO-20/Sp and PAO/MgO-20 nano-liquids increases as the nano-particle content increases from 0 to 0.0025%. This effect is attributed to the rapid increase in electron shallow trap density [1]. The maximum breakdown voltage indicates that the maximum density of electrically active traps is formed in PAO oil when the MgO nano-particle concentration is 0.0025%. When the MgO nano-particle concentration exceeds 0.0025%, surface effects occur, leading to an increase in the tendency of the nano-particles to aggregate as they reach saturation concentration. As a result, the density of electrically active traps decreases, and the breakdown voltage decreases [2]. We have included these explanations in the revised manuscript.

References:

[1] Y. Du et al., “Effect of electron shallow trap on breakdown performance of transformer oil-based nanofluids,” in Journal of Applied Physics, 2011. doi: 10.1063/1.3660783.

[2] Y. Lv, L. Wang, X. Li, Y. Du, J. Zhou, and C. Li, “Experimental investigation of breakdown strength of mineral oil-based nanofluids,” in 2011 IEEE International Conference on Dielectric Liquids, 2011, pp. 1–3. doi: 10.1109/ICDL.2011.6015446.

Point 4: The authors wrote that MgO nanoparticles were used also with other base-fluids (like water, ethylene glycol, kerosene, engine and insulating oils, etc.), apart from PAO. Thus, in my opinion, for the convenience of readers the authors should discuss better and compare (or provide the corresponding references) the benefits of usage of PAO with respect to other base-fluids. Does MgO with PAO provide better thermal and dielectrical properties than MgO with other base-fluids?

Response:

Thank you for your valuable contribution. The comparison of the thermal and electrical insulation properties of nano MgO liquid with other base liquids will be addressed in our next review article, which is expected to be submitted soon. Based on your suggestions, we have included the citations in the revision manuscript.

References:

1. Żyła, G. Viscosity and Thermal Conductivity of MgO–EG Nanofluids: Experimental Results and Theoretical Models Pre-dictions. J Therm Anal Calorim 2017, 129, doi:10.1007/s10973-017-6130-x.
2. Asifa, Talha Anwar, Poom Kumam, Shah Muhammad, New Fractional Model to Analyze Impacts of Newtonian Heating, Shape Factor and Ramped Flow Function on MgO–SiO2–Kerosene Oil Hybrid Nanofluid. Case Studies in Thermal Engineering 2022, 38, 102361, doi:10.1016/J.CSITE.2022.102361.

Point 5: Finally, the manuscript must undergo more careful checking/proofreading in English (e.g., “oil” instead of “Oil” in line 60 on page 2, etc.)

Response:

Thank you for the suggestion. We have asked a native speaker to read and proofread our manuscript in the revised manuscript.

Point 6: The authors consider nanofluids (being MgO nanoparticles immersed into the oil) which can generally be also viewed as colloidal systems or systems of solutes immersed into the solvents with different dielectric constants (different from those of solutes). Albeit the authors’ work is almost purely experimental, but inclusion the recent works [1–3] (specialized mostly on building the analytical approximations for the electrostatic interactions) in the list of references of the manuscript could be useful for the sake of the presentation broadening and for readers in giving them a good prospect of the-state-of-the-art electrostatic issues of manuscript’s topics. Also, I find it useful to include the very recent topical review [4] (it is mostly devoted to molten salts, but in general contains a quite wide overview of various issues on nanofluids with non-organic and organic nanoparticles).

References

[1] I.N. Derbenev, A.V. Filippov, A.J. Stace, E. Besley, Electrostatic interactions between charged dielectric particles in an electrolyte solution: constant potential boundary conditions, Soft Matter, 14, 5480–5487, (2018).

[2] S.V. Siryk, A. Bendandi, A. Diaspro, W. Rocchia, Charged dielectric spheres interacting in electrolytic solution: a linearized PoissonBoltzmann equation model, Journal of Chemical Physics, 155, 114114, (2021).

[3] L. Wu, B. Gao, Y. Tian, R. Munoz-Carpena, K. J. Zigler, DLVO interactions of carbon nanotubes with isotropic planar surfaces. Langmuir, 29, 3976-3988, (2013).

[4] X. Chen, M. Zhang, Y. Wu, C. Ma, Advances in high-temperature molten salt-based carbon nanofluid research, Energies, 16 (5), 2178, (2023).

Response:

Thank you for your suggestion. We have carefully read the articles you mentioned. These articles have provided us with new ideas for our research. We will cite them in our future studies.

Reviewer 2 Report

This study examined the effect of adding magnesium oxide nanoparticles to polyalphaolefin (PAO) oil, resulting in nanofluids with improved heat transfer and dielectric properties. PAO/MgO nanofluid-based dielectric fluid could be utilized as a protective coating for electronic equipment in various industries. Although the results in the draft are somewhat interesting,  some physical discussion looks missing. For example, the authors did not clearly explain the graph's nonlinearity (local maximum or local minimum). There exists an optimum concentration that produces the highest breakdown voltage. Why? Also, the thermal conductivity starts to increase suddenly after 40 degrees (Figure 6). Why? I suggest reconsidering this article after adding further detailed discussion about the results. 

English is moderate. It's readable. 

Author Response

Dear Reviewer,

Thank you very much for the review of our manuscript. We sincerely appreciate all the valuable comments and suggestions that reviewers gave us. Relying on those insightful comments and suggestions helps us to improve our article in the current version. We carefully considered all comments, made the appropriate changes, and included them in the manuscript. In addition, we also add explanations suggested by reviewers. We hope that after the revised manuscript you find our manuscript suitable for publication and look forward to hearing from you in due course. Authors always welcome constructive comments if any. All modifications in the manuscript have been highlighted in red.

This study examined the effect of adding magnesium oxide nanoparticles to polyalphaolefin (PAO) oil, resulting in nanofluids with improved heat transfer and dielectric properties. PAO/MgO nanofluid-based dielectric fluid could be utilized as a protective coating for electronic equipment in various industries. Although the results in the draft are somewhat interesting, some physical discussion looks missing.

Point1: For example, the authors did not clearly explain the graph's nonlinearity (local maximum or local minimum). There exists an optimum concentration that produces the highest breakdown voltage. Why?

Response:

Thank you for the question. The breakdown voltage of PAO/MgO-20/Sp and PAO/MgO-20 nano-liquids increases as the nano-particle content increases from 0 to 0.0025%. This effect is attributed to the rapid increase in electron shallow trap density [1]. The maximum breakdown voltage indicates that the maximum density of electrically active traps is formed in PAO oil when the MgO nano-particle concentration is 0.0025%. When the MgO nano-particle concentration exceeds 0.0025%, surface effects occur, leading to an increase in the tendency of the nano-particles to aggregate as they reach saturation concentration. As a result, the density of electrically active traps decreases, and the breakdown voltage decreases [2]. We have included these explanations in the revised manuscript.

References:

[1] Y. Du et al., “Effect of electron shallow trap on breakdown performance of transformer oil-based nanofluids,” in Journal of Applied Physics, 2011. doi: 10.1063/1.3660783.

[2] Y. Lv, L. Wang, X. Li, Y. Du, J. Zhou, and C. Li, “Experimental investigation of breakdown strength of mineral oil-based nanofluids,” in 2011 IEEE International Conference on Dielectric Liquids, 2011, pp. 1–3. doi: 10.1109/ICDL.2011.6015446.

Point 2: Also, the thermal conductivity starts to increase suddenly after 40 degrees (Figure 6). Why? I suggest reconsidering this article after adding further detailed discussion about the results.

Response:

The results show that as the ambient temperature increases, the thermal conductivity of PAO oil and PAO/MgO-20/Sp nano-liquid increases. At every temperature point between 30 and 50 ºC, the thermal conductivity of PAO/MgO-20/Sp nano-liquid is higher than that of PAO oil. Compared to PAO oil, the thermal conductivity of the nano-liquid increases by 1.58 times at 30 ºC and 1.38 times at 50 ºC. The thermal conductivity of nano MgO-20 is 48.8 W/m.K [6], significantly higher than the experimental value of 0.327 W/m.K for PAO oil. Therefore, increasing the concentration of nano MgO-20 in PAO oil increases the thermal conductivity of the nano-liquid. Additionally, the surface effects of nano MgO particles with an average size of 20 nm also contribute to the increase in thermal conductivity of PAO/MgO-20/Sp nano-liquid. As the temperature increases, the collision density of nano MgO particles in PAO oil increases, enhancing Brownian motion between the particles and reducing particle aggregation caused by decreased surface energy [3]-[5].

         The results also show that the thermal conductivity of PAO oil and nano PAO/MgO-20/Sp fluid increases rapidly when the temperature reaches 40 ºC. This can be explained by the nature of the hydrocarbon molecules in the PAO oil studied, which have a relatively high dynamic viscosity of 30.8 cSt at 40 ºC due to their relatively large average molecular weight. At temperatures between 30÷40, the hydrocarbon molecules in the PAO oil begin to move restrictedly, but the free volume does not increase much. When the temperature reaches 40-50 ºC, the hydrocarbon molecular chains begin to move faster, the distance between the molecules increases, the interaction forces between the molecules decrease, and the viscosity decreases, or in other words, it increases the flexibility of the atoms [5]. Therefore, the thermal conductivity starts to increase rapidly at this temperature.

         References:

[3] Li Yu-Hua, Qu Wei, and Feng Jian-Chao, “Temperature Dependence of Thermal Conductivity of Nanofluids,” Chinese Physics Letters, vol. 25, no. 9, p. 3319, 2008, doi: 10.1088/0256-307X/25/9/060.

[4]     S. Kumar et al., “Enhanced Heat Transfer Using Oil-Based Nanofluid Flow through Conduits: A Review,” Energies (Basel), vol. 15, no. 22, 2022, doi: 10.3390/en15228422.

[5]     S. Simpson, A. Schelfhout, C. Golden, and S. Vafaei, “Nanofluid Thermal Conductivity and Effective Parameters,” Applied Sciences, vol. 9, no. 1, 2019, doi: 10.3390/app9010087.

[6]     W. Yu and H. Xie, “A Review on Nanofluids: Preparation, Stability Mechanisms,  and Applications,” J Nanomater, vol. 2012, p. 435873, 2012, doi: 10.1155/2012/435873.

Reviewer 3 Report

Dear Author,

My review report is attached.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for the review of our manuscript. We sincerely appreciate all the valuable comments and suggestions that reviewers gave us. Relying on those insightful comments and suggestions helps us to improve our article in the current version. We carefully considered all comments, made the appropriate changes, and included them in the manuscript. In addition, we also add explanations suggested by reviewers. We hope that after the revised manuscript you find our manuscript suitable for publication and look forward to hearing from you in due course. Authors always welcome constructive comments if any. All modifications in the manuscript have been highlighted in red.

Point 1: The paper title should be written in capital and small letters. i.e. Highly Improved Dielectric and Thermal Performance of Polyalphaolefin Oil-Based Fluids Using MgO Nanoparticles.

Response:

Thank you for your suggestion. We completely agree with your suggestion and have corrected the title of the article to "Highly Improved Dielectric and Thermal Performance of Polyalphaolefin Oil-Based Fluids Using MgO Nanoparticles."

Point 2: This paper was submitted to Special Issue: Advances in Oxide Thin Films and Nanostructures https://www.mdpi.com/journal/coatings/special_issues/937TKEE1MF

The authors should show why this manuscript: Highly Improved Dielectric and Thermal Performance of Polyalphaolefin Oil-Based Fluids Using MgO Nanoparticles is relevant to the scope of Special Issue: Advances in Oxide Thin Films and Nanostructures in Coatings Journal.

Response:

         Thank you very much for the question. In this Special Issue “Advances in Oxide Thin Films and Nanostructures”, we aim to compile innovative and cutting-edge technological applications and the production and characterization of oxide materials. One of the topics of this special issue is Oxides for electronic and quantum applications. Our study investigated the effects of adding magnesium oxide nanoparticles to polyalphaolefin (PAO) oil, creating a nano-fluid with improved dielectric and thermal properties. The PAO/MgO nano-fluid can be used as a protective coating for electronic devices in various industries. Therefore, I believe that the content of our study is suitable for the requirements of the special issue: “Advances in Oxide Thin Films and Nanostructures”.

Point 3: It is better to add some equations to the manuscript. For example, how to calculate the nanofluid concentration either by mass or by volume.

Response:

The concentrations of the nano-liquid in the article are calculated as weight percentages. They are easily performed using an analytical balance with an error of up to 0.0001. In addition, we prepared a sample mass of 1 kg for each nano-liquid tested. Therefore, We think including the calculation formula in the article is not really necessary.

Point 4:  For Table 1. Specifications of MgO nanoparticles It is better to add the reference sources (where do the authors get these values?)

Response:

Thank you for the question. The technical specifications of the MgO nanoparticles were obtained from the quality certificate provided by the supplier manufacturer.

Point 5: In 2.2. Preparation of PAO/MgO nanofluids The nanofluid is prepared by dispersing MgO nanopowder at the concentrations: 0, 0.001, 0.002, 0.0025, 0.003, 0.005 by weight percent in polyalphaolefin oil (PAO). To obtain nanofluid, the mixtures are stirred for 20 minutes, then ultra-sonicated using a probe ultrasonicator (VCX 500, Reviewer Comments on Manuscript Number: coatings-2366288 2 Sonics, USA) with a power of 500 W at a frequency of 20 kHz for 90 minutes. To remove air bubbles and moisture content, nanofluids are dried at 80oC, with a pressure of 100 mbar for 4 hours.

The authors carried out an experimental study. Therefore, it is better to add uncertainty analysis.

Response:

Thank you for your insightful feedback. The breakdown voltage values are very sensitive to changes in the measurement conditions. In fact, we conducted six consecutive measurements for each test sample to account for the variation in the breakdown voltage values. The machine gave a different set of six breakdown voltage values for each measurement. The average value and the standard deviation of the breakdown voltage are presented in the manuscript.

However, for other electrical and thermal properties (bulk resistivity, dielectric constant, thermal conductivity), the measurement uncertainties are very small, and the values of multiple measurements are very close to each other. Therefore, for these results, we only used the average value of the measurements.

Poin 6: For these references,

16. J. Hornak et al., “Magnesium Oxide Nanoparticles: Dielectric Properties, Surface Functionalization and Improvement of Epoxy-Based Composites Insulating Properties,” Nanomaterials, vol. 8, no. 6, 2018, doi: 10.3390/nano8060381.
17. S. Hu et al., “Surface-modification effect of MgO nanoparticles on the electrical properties of polypropylene nanocomposite,” High Voltage, vol. 5, no. 3, pp. 249–255, 2020, doi: https://doi.org/10.1049/hve.2019.0159.
18. M. M. Emara et al., “Dielectric and Thermal Performance of Natural Ester Oil Based Nanofluid with Magnesium Oxide Nano-particles,” in 2022 IEEE 21st International Conference on Dielectric Liquids (ICDL), 2022, pp. 1–6. doi: 10.1109/ICDL49583.2022.9830951.
19. Y. Du et al., “Effect of electron shallow trap on breakdown performance of transformer oilbased nanofluids,” in Journal of Applied Physics, 2011. doi: 10.1063/1.3660783.
20. S. Kumar et al., “Enhanced Heat Transfer Using Oil-Based Nanofluid Flow through Conduits: A Review,” Energies (Basel), vol. 15, no. 22, 2022, doi: 10.3390/en15228422.

Please write all the authors names. Do not use et al.

Response:

Thank you for your suggestion. We have fully included the names of the authors of the listed references.

Point 7: When reviewing the references, a strong impression can be created that the manuscript should be submitted to another journal: To give journal readers a sense of continuity, the reviewer encourages the author to identify present journal publications of similar research in your papers. REFERENCES section has NONE PUBLISHED PAPERS in Coatings. The relevance to Coatings should be enhanced with the considerations of scope and readership of the Journal by adding some published papers in Coatings to REFERENCES section.

Response:

We chose Coatings journal to publish our paper because we knew it was one of the reputable specialized journals that scientists all over the world choose to publish their research results. In addition, we found some publications on nano fluids in the Coatings journal (such as graphene nano fluid, hybrid nano fluid, metal nano fluid, metal oxide nano fluid, etc.), but there were not many publications on metal oxide nano fluid. In our paper, we used one citation (reference 8) published in the Coatings journal because it was relevant to the content we were studying.

Round 2

Reviewer 2 Report

Since the authors have fully addressed the my comments, I recommend the publication of this article without further revision.

This article is readable. So, I don't think that the English editiing is necessary.