Investigation of tetracosane thermal transport in presence of graphene and carbon nanotube fillers––A molecular dynamics study

doi:10.1016/j.est.2020.101321

Journal of Energy Storage

Volume 29, June 2020, 101321

https://doi.org/10.1016/j.est.2020.101321 Get rights and content

Highlights

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Thermal properties of pure and mixed paraffin were examined by molecular dynamics.
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Heat capacity, PDOS, density, RDF, MSD and thermal conductivity were measures.
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Graphene and CNT increases the thermal conductivity of the tetracosane.
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Graphene and CNT decrease the molecular movement and its thermal capacity.
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CNT is better than graphene to increase the thermal conductivity of tetracosane.

Abstract

This paper examines the thermal properties of pure tetracosane paraffin, tetracosane-graphene, and tetracosane-carbon nanotube mixed phase change materials (PCM). The most important properties studied were thermal capacity in constant volume (C_v), mean square displacement of atoms (MSD), radial distribution function (RDF), density, phonon density of states (PDOS) and thermal conductivity (k) under different temperatures. The results show that graphene and carbon nanotube increase the thermal conductivity of the tetracosane at different temperatures, but decrease the molecular movement and its thermal capacity (except after about 360 K), and it can be said that this slightly decreases the paraffin melting temperature. It was demonstrated that carbon nanotube is more efficient than graphene to increase the thermal conductivity of the proposed PCM.

Introduction

Thermal energy storage is achieved by various techniques: sensible heat storage, latent heat storage, thermochemical heat storage, or a combination of these methods [1]. Phase change materials (PCMs) are used to store latent heat [2] and these materials have attracted much attention in recent years [3,4]. When the material moves from solid to liquid or vice versa, the latent heat is absorbed or released. Substances that are required as phase-change materials for storing thermal energy must have high latent heat and high thermal conductivity [5]. Paraffin is composed of alkaline chains (C_nH_2n+2), which has high latent heat, wide temperature range for phase change and stable chemical properties [6,7]. It is also easy to obtain and is much cheaper than other phase-change substances such as metals and molten salts. Phase change materials, especially paraffin, have some defects, most notably low thermal conductivity [8,9]. Adding nanomaterials to pure PCM can result in better thermal storage properties in PCM. The effect of nano-additives on PCMs includes increasing the thermal conductivity, changing the fuzzy change characteristics (temperature range and phase change heat), and increasing the thermal stability of PCMs [10,11].

The investigations include empirical studies and numerical simulations. In experimental cases, various studies focused on the production of paraffinic PCM composites under the addition of thermal superconductors [12]. The effects of nanofillers on the thermal properties of paraffin were investigated by Wu et al. [13]. They showed that carbon nanoparticles have a significant effect in increasing the thermal conductivity of paraffin. The composite of paraffin-graphene experienced the maximum growth in thermal conductivity up to 52.4% with a weight fraction of 3% of graphene. In another study, graphene nanoplatelets were used to increase the thermal conductivity of n-eicosane [14]. In the highest amount of this nano-additive (10% by weight), the thermal conductivity increased by 400% at 10 °C. Warzoha and Fleischer [15] claim that the number of graphene layers significantly affects the thermal conductivity of paraffin. They claimed that the thermal conductivity of the paraffin can be adjusted by adding graphene nanosheets. Wu et al. [16] examined the effect of adding different amounts of graphene sheets on the thermo-physical properties of PCMs. The results of their investigations showed that thermal enthalpy of PCMs gradually decreases with the increasing amount of graphene sheets, although the heat transfer efficiency and thermal stability improved and increased, respectively.

Some molecular dynamics studies have been performed to study the enhancing thermal conductivity of PCMs by adding nano additives. Dr. Babaei et al. [17] designed and simulated octadecane (C₁₈H₃₈) with carbon nanotubes and graphene. They fixed the nano-additives and forced them to be motionless, to study just the paraffin's molecules behaviors using NERD potential. They illustrated that adding carbon nanotubes and graphene increases the thermal conductivity and also, reduces the thermal resistance of PCM. Mixtures of nonadecane (C₁₉H₄₀), nonadecane-graphene and nonadecane-graphene oxide were simulated by Huang et al. [18]. They used Universal forcefield to carry out all the simulations. The nanoparticles' size was 2.5 × 2.5 nm. Regarding their simulation, the thermal conductivity of pure paraffin was 0.373 W/mK. However, the thermal conductivity of a 10% composite by weight of strong paraffin-graphene sheets obtained about 0.488 W/mK, while the thermal conductivity of solid paraffin-graphene oxide in the same weight percent was 0.506 W/mK. Researchers concluded that graphene oxide increases the thermal conductivity much more than graphene.

In this work, we used molecular dynamics simulations to investigate the thermal properties of tetracosane paraffin (C₂₄H₅₀), which is used as a phase change material [19,20]. This PCM commonly is used in Li-ion batteries and other electronic devices for thermal management or can be used for other TES (thermal energy storage) applications [21]. The addition of graphene and carbon nanotube to tetracosane has not yet been investigated. Namely, in the literature and molecular dynamics modeling, a limited size of nano-additives was allocated. However, in this study, by using periodic boundary conditions and adjusting nanoparticles' boundaries to the simulation box surfaces, an unlimited (infinite) size of them is being assumed. Besides, in this paper, PCFF forcefield for paraffin is newly used for a wide range of thermal properties of paraffin. We calculate the mean square displacements (MSD), heat capacity, radial distribution function (RDF), density, phonon density of states (PDOS), and thermal conductivity. Our main approach was to study the effect of adding graphene and carbon nanotubes on the thermal conductivity of this material (n-tetracosane). The used force fields in molecular dynamics simulations, modeling structures, simulation trends and computational methods are explained in Section 2. The results and discussions are presented in Section 3. Finally, the conclusions are presented in Section 4.

Section snippets

Materials and methods

In this study, the molecular dynamics simulation method was utilized [22], which is unable to model the electrons. Therefore, the thermal transport in this study is just for phonon transports.

PCFF¹ force field was used for interaction of alkanoic material (paraffin tetracosane) [23], [24], [25], [26]. The Tersoff potential (1989) was used to describe the carbon-carbon interaction in graphene and carbon nanotube structures [27]. For Van der Waals's interaction

Results and discussions

In this section, thermal and structural properties, including C_v, MSD, RDF, PDOS, and thermal conductivity of pure tetracosane, tetracosane-graphene, and tetracosane-CNT composites are represented. As the first achievement, after NPT equilibration (at 330 K), the density of tetracosane was measured as 0.7317 g/cm³, which is compatible with experimental value (0.7736 g/cm³ at 335 K) reported in previous studies [19]. Also, the thermal conductivity of pure tetracosane at 330 K in x and

Conclusion

Different solutions have been proposed to solve the problem of low thermal conductivity of paraffin as a phase change material. One of these ways is the addition of nano-superconductive materials such as graphene and carbon nanotube (CNT), which has been focused on in this study. The paraffin used is tetracosane (C₂₄H₅₀), commonly used for thermal management of batteries and electronic devices. Computing the density of simulated structures at different temperatures shows that by adding

Author statement

Hossein Tafrishi developed the theory and performed the computations and wrote the manuscript with support from Sadegh Sadeghzadeh.

Sadegh Sadeghzadeh verified the analytical methods and supervised the findings of this work.

Rouhollah Ahmadi helped supervised the project

Fatemeh Molaei provided the computational system

Farrokh Yousefi contributed to the final version of the manuscript

Hamidreza Hassanloo helped in writing and analysis

All authors discussed the results and contributed to the final

Declaration of Competing Interest

None.

Funding

No funding was received for this work.

Intellectual property

We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property.

Category 1: conception and design of study

Conception: Hossein Tafrishi, Sadegh Sadeghzadeh, Rouhollah Ahmadi

Design of study: Hossein Tafrishi, Sadegh Sadeghzadeh, Rouhollah Ahmadi

Acquisition of data: Hossein Tafrishi1, Fatemeh Molaei, Hamidreza Hassanloo

Analysis and/or interpretation of data: Hossein Tafrishi, Sadegh Sadeghzadeh, Farrokh Yousefi

Category 2: drafting the manuscript

Preparing the manuscript: Hossein Tafrishi, Hamidreza Hassanloo

Revising the manuscript critically for important intellectual content: Sadegh Sadeghzadeh,

Rouhollah Ahmadi, Fatemeh Molaei, Farrokh

Acknowledgements

This work has been supported by the High-Performance Computing Research Center (HPCRC) - Akmirkabir university of Technology under Contract No ISI-DCE-DOD-Cloud-700101–3533.

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Investigation of tetracosane thermal transport in presence of graphene and carbon nanotube fillers––A molecular dynamics study

Highlights

Abstract

Introduction

Section snippets

Materials and methods

Results and discussions

Conclusion

Author statement

Declaration of Competing Interest

Funding

Intellectual property

Category 1: conception and design of study

Category 2: drafting the manuscript

Acknowledgements

Renew. Sustain. Energy Rev.

Prog Mater. Sci.

Renew. Sustain. Energy Rev.

Renewable Sustainable Energy Rev.

Appl. Energy

Energy Convers. Manage.

Renew. Sustain. Energy Rev.

Renew. Sustain. Energy Rev.

Int. J. Heat Mass Transf.

Int. J. Heat Mass Transf.

Appl. Energy

Sol. Energy

Energy Convers. Manage.

Comput. Theor. Polym. Sci.

J. Comput. Phys.

Appl. Therm. Eng.

Energy Technol.

Int. J. Heat Mass Transf.