In an article published in the open access journal Scientific Reports, the researchers prepared carbon-based nanofluids (CbNF) using a two-step method and determined their thermal conductivity (λ) and diffusivity (α). These CbNFs were said to significantly improve the characteristics of basic working fluids.
Study: Thermal conductivity and thermal diffusivity of sheet-based nanofluids. Image credit: Angel Soler Gollonet / Shutterstock.com
A highly stable fullerene (C60) NF in the liquid phase was analyzed using the current hot wire technique to measure λ at a temperature ranging from 254 to 323 kelvins.
Nanofluids in heat transfer and cooling technology
In recent years, CbNFs have played an important role in the preparation of nanofluids (NFs) due to their excellent thermal properties related to conventional liquids. NFs are nanometer-sized particles formed with conventional fluids (oil, water, glycerol, etc.). The molecular bond that CbNFs share with BLs affects thermal and electrical conductivity and light absorption / emission characteristics. Due to their excellent thermal properties, these materials are used for industrial purposes such as thermal storage and heat pipes.
Previous research by researchers has shown an improvement in the λ of NFs as a function of the BFs used. The disadvantage of these NFs is that the value of λ is unstable and changes depending on various preparation parameters such as basic fluids (BF), NF concentration and surfactants. According to the researchers, to achieve a stable value of λ, surfactants are used in BFs to prevent cluster formation. One of the reasons for the apparent inconsistencies in numerous published articles on these measures is the stability of NFs.
As a result, NF-based graphene nanomaterials and carbon nanotubes have been the focus compared to C60-based NFs. The current work focuses on a thorough analysis of the thermal properties of BFs.
Preparation of CbNFs
In the present study, the researchers used a two-step method to prepare NF. The BLs used were 1,2,3,4 tetrahydronaphthalene (C10H12) and 1,2 dichlorobences (C6H4Cl2). Later, dry C60 was added to the BLs with continuous stirring and then ultrasound was performed for successive 30 minute intervals to remove any agglomeration.
The mixture was then allowed to stand overnight to ensure that the nanoparticles did not precipitate. It is important to note that no fullerene contamination was observed for the duration of the experiments. Values λ and α were measured using the transient multicurrent hot wire experimental apparatus with a temperature range of 254-323 kelvin at atmospheric pressure. Electrical measurements were analyzed using the Keithley 2400 source meter and analysis data were correlated using proposed theoretical models.
Stable CbNFs showed high conductivity
CbNF was synthesized in an extremely steady state without using any surfactant and two BFs, thus achieving high conductivity. The conductivity value obtained in this study is very much in line with the only reported value 27 years ago. In the case of C6H4Cl2, no published data are available, so no comparison can be made. λ decreased with increasing C60 concentration in NFs. To clarify the abnormal improvement of NFs, the experimental results were compared with those predicted by several theoretical models of thermal conductivity. However, in this model, λ is overestimated at high concentrations of C60 in nanoparticles because the model does not take λ into account.
In general, Brownian C60 movement was not observed in any of the NFs studied. There was no discernible relationship between α and temperature for C10H12. When the temperature rose from 254 to 323 kelvins, there was a smaller drop in C6H4Cl2.
Conclusions
In summary, the researchers in the present study investigated both λ and α of CbNF with two basic liquids – C10H12 and C6H4Cl2 – using a transient multi-current hot cable at atmospheric pressure and temperatures ranging from 254 to 323 kelvins. Improving the λ value using a small amount of nanoadditive is considered abnormal and controversial. He also noted that the acquired values of 1,2,3,4-tetrahydronaphthalene are extremely close to those found in articles published more than 25 years ago, indicating the accuracy of the proposed hot wire measurements.
The authors strongly believe that with the addition of C60 to NFs, conductivity is reduced. There is also a close agreement between the results achieved and those expected by applying various theoretical models of thermal conductivity. Further theoretical research is required to accurately state the regulatory mechanism or mechanisms and to explain the variation of thermal conductivity and diffusivity in this research work.
Reference
Reding, B., Khayet, M. (2022). Thermal conductivity and thermal diffusivity of fullerene-based nanofluids. Science Rep 12, 9603 https://doi.org/10.1038/s41598-022-14204-y
Disclaimer: The views expressed herein are those of the author, which are privately expressed and do not necessarily represent the views of AZoM.com Limited T / A AZoNetwork, the owner and operator of this website. This disclaimer is part of the Terms and Conditions of Use of this website.