Evaluation of thermal conductivity of organic phase-change materials from equilibrium and non-equilibrium computer simulations: Paraffin as a test case

Nazarychev, Victor M.; Glova, Artyom D.; Volgin, Igor V.; Larin, Sergey V.; Lyulin, Sergey V.; Gurtovenko, Andrey A.

doi:10.1016/j.ijheatmasstransfer.2020.120639

Cited by 34 publications

(31 citation statements)

References 45 publications

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“…As we proceed to show, crystallization as well as many thermophysical, structural, and dynamic properties of n-eicosane depend critically on the rate with which cooling is performed in computer simulations. This implies that the cooling rate is one of the most important parameters of computer modeling of paraffins, along with force fields [15][16][17][18] and various algorithms for calculating the thermal conductivity [17,18]. Our computational findings could therefore serve as a basis for an accurate description of the crystallization behavior of organic PCMs such as paraffins.…”

Section: Introductionmentioning

confidence: 88%

“…Recently, we showed that this force field provided a reasonable description of the thermophysical, structural, and dynamic properties of n-eicosane [15]. Furthermore, this force field was found to outperform 9 other atomistic force fields as far as the thermal conductivity is concerned [17]. A paraffin sample consisted of 1000 n-eicosane chains, so that the total number of atoms in a system amounted to 62000.…”

Section: Methodsmentioning

confidence: 99%

“…For our purposes, we chose to consider n-eicosane (C 20 H 42 ); this short n-alkane was shown to have a great potential for the use in domestic heat storage devices [1]. Recently, the properties of n-eicosane were a subject of extensive computational studies with the use of 10 different atomistic models [15][16][17][18]. Furthermore, experimental data are also available for this n-alkane, which is very important in terms of validating simulation results.…”

Section: Introductionmentioning

confidence: 99%

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Cooling-rate computer simulations for the description of crystallization of organic phase-change materials

Nazarychev

Glova

Larin

et al. 2022

Preprint

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A molecular-level insight into the phase transformations is of great demand for the molecular systems for which the phase transition is a key process from the point of view of practical applications, organic phase-change materials being one of the most prominent examples. Such a detailed insight can be gained through cooling-rate computer simulations, i.e. simulations in which cooling is applied to a system at a constant rate. However, the ability of the simulations to give an accurate description of the phase transition process is an open question, since the cooling rates accessible in atomic-scale computer simulations are many orders of magnitude larger than those in experiments. In this paper we present the first computational study that systematically explores as to how the cooling rate affects the crystallization of organic phase-change materials such as paraffins. To this end, we performed a series of atomistic molecular dynamics simulations in which the cooling rate was varied over four orders of magnitude. Our computational results clearly show that a certain threshold in the values of cooling rates exists. When cooling is performed with the rates smaller than the threshold, computer simulations are able to qualitatively reproduce the crystallization process in paraffins. This includes an abrupt change in the temperature dependence of the density, enthalpy, and thermal conductivity upon crystallization. The crystallization enthalpy for these cooling rates was found to agree quantitatively with experiment. However, beyond this threshold, when cooling is too fast, the paraffin’s properties in simulations start to deviate considerably from experimental data: the faster the cooling, the larger part of the system is trapped in the super-cooled liquid state. As a result, one can observe a systematic decrease in the fraction of crystalline domains in a paraffin sample with cooling rate, leading eventually to a complete lack of crystallization at low temperatures. Both the crystallization temperature and the crystallinity decrease with cooling rate in line with experimental data. All the above strongly supports the conclusion that a proper choice of a cooling rate is of tremendous importance in computer simulations of organic phase-change materials such as paraffins. Cooling with the rates that are too high can lead to a completely inaccurate description of the crystallization process, as well as the thermophysical and structural properties.

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Section: Introductionmentioning

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cooling-rate computer simulations for the description of crystallization of organic phase-change materials

Nazarychev

Glova

Larin

et al. 2022

Preprint

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“…All MD simulations in the present study have been carried out using the all-atom General Amber Force Field (GAFF) [25] which was previously shown to give accurate results [24] for TC of paraffin. Polyethylene chains were drawn with Amber-Tools20 (ambermd.org), and together with the force-field parameters made ready for simulation in the GROMACS MD software package [26,27] using AnteChamber PYthon Parser interfacE (ACPYPE) [28,29] .…”

Section: Simulation Details and Analysis Methodsmentioning

confidence: 99%

Effects of Branching and Polydispersity on Thermal Conductivity of Paraffin Waxes

Boomstra¹,

Asseldonk²,

Geurts³

et al. 2022

SSRN Journal

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“…As an important thermal property parameter for the practical application of PCM, thermal conductivity was calculated here using the nonequilibrium molecular dynamics. − According to Fourierʼs law, the thermal conductivity can be expressed as where A is the cross-sectional area of the model, Q is the heat through the cross-sectional area, x 1 and x 2 are the distances between the heat sink and heat sources, and T is the temperature. The calculation of thermal conductivity was not involved in previous research of optically controlled phase change materials.…”

Section: Simulation Detailsmentioning

confidence: 99%

Molecular Dynamics Study of Optically Controlled Phase Change Materials

Wang

Shi

et al. 2022

J. Phys. Chem. C

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The optically controlled phase change technology makes the phase change material produce an obvious energy barrier between a solid and a liquid, which can effectively prevent spontaneous heat loss. Based on the molecular dynamics method, the microscopic model of the optically controlled composite system (capric acid/4-(phenyldiazenyl)phenyl decanoate) was established and the simulation of the AZO trans−cis isomerization process was based on the modification of the dihedral angle parameters of AZO in the condensed phase. A theoretical method for predicting the temperature of optically controlled phase transition was proposed, and the reason for the temperature difference caused by isomerization was analyzed. At a given molar concentration (30 mol %), the cis and trans phase transition temperature, which shows a temperature difference of 4.49 K, results from the destruction of molecular symmetry and the differences in the aggregation and nucleation ability of the dopant before and after photoisomerization. Experiments verify the reliability of the method. In addition, the analysis of the thermal conductivity of the composite systems was conducted based on the nonequilibrium molecular dynamics method. No matter whether the azophenyl group is a cis structure or a trans structure, doping slightly weakens the thermal conductivity of the raw material due to the destruction of the ordered lattice structure. Aggregation and nucleation of trans-azophenyl groups lead to a higher degree of order of the fatty acid chain than that of the corresponding cis system, resulting in higher thermal conductivity, which can be explained quantitatively by the order parameter. This study provides theoretical support for the thermophysical properties and formation reasons of optically controlled phase change materials containing the azophenyl group and provides ideas for the improvement, development, and application of such materials in the future.

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Evaluation of thermal conductivity of organic phase-change materials from equilibrium and non-equilibrium computer simulations: Paraffin as a test case

Cited by 34 publications

References 45 publications

Cooling-rate computer simulations for the description of crystallization of organic phase-change materials

Cooling-rate computer simulations for the description of crystallization of organic phase-change materials

Effects of Branching and Polydispersity on Thermal Conductivity of Paraffin Waxes

Molecular Dynamics Study of Optically Controlled Phase Change Materials

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