Interpretation of apparent thermal conductivity in finite systems from equilibrium molecular dynamics simulations

Dong, Hai-Kuan; Xiong, Shiyun; Fan, Zheyong; Qian, Ping; Su, Yanjing; Ala-Nissilä, Tapio

doi:10.1103/physrevb.103.035417

Cited by 13 publications

(15 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Despite of the zero value in the infinite-time limit, the RTC in these finite systems exhibits a clear maximum value κ EMD max at a particular correlation time τ max . In our previous work [13], this maximum value has been interpreted as the apparent thermal conductivity in the finite systems. Similar to Ref.…”

Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

“…While it has been believed that the EMD method can only be used to compute the thermal conductivity in the diffusive limit, we have recently shown [13] that it can also be used to compute the apparent thermal conductivity (also called the effective thermal conductivity) of finite systems. For a finite system with nonperiodic boundary conditions applied to the transport direction, the running thermal conductivity (RTC) based on the Green-Kubo relation will eventually converges to zero in the limit of infinite-time, but it has been argued [13] that the maximum value of the RTC can be interpreted as the apparent thermal conductivity of the finite system. However, it was found that the apparent thermal conductivity as computed from the EMD method for a system with domain length 2L is equal to that as computed from the NEMD method for a system with domain length L. This difference between the domain length is puzzling and in this work we show that it is related to the choice of simulation setups in the NEMD method: if the NEMD is performed with periodic boundary conditions, instead of fixed boundary conditions, in the transport direction, the thermal conductivity values from EMD and NEMD will agree for the same domain length.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Exactly equivalent thermal conductivity in finite systems from equilibrium and nonequilibrium molecular dynamics simulations

Dong

Fan²,

Qian³

et al. 2022

Physica E: Low-dimensional Systems and Nanostructures

Self Cite

View full text Add to dashboard Cite

Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Exactly equivalent thermal conductivity in finite systems from equilibrium and nonequilibrium molecular dynamics simulations

Dong

Fan²,

Qian³

et al. 2022

Physica E: Low-dimensional Systems and Nanostructures

Self Cite

View full text Add to dashboard Cite

“…In Sec. II, the boundary conditions in AEMD and NEMD follow the settings of most previous papers [12,21,32,34]. In AEMD, periodic boundary conditions are applied in all directions, while in NEMD, fixed boundary conditions are applied in the direction of heat conduction.…”

Section: Definition Of the Sizementioning

confidence: 99%

“…Molecular dynamics (MD) is a widely used atomistic simulation method for the investigation of nanoscale thermal transport [1][2][3][4][5][6][7][8][9][10]. Several MD methods have been developed to simulate thermal transport process in the past few decades, including equilibrium molecular dynamics (EMD) [11][12][13][14], and nonequilibrium molecular dynamics (NEMD) [1][2][3]. EMD is based on the fluctuation-dissipation theorem and the bulk thermal conductivity can be extracted from the heat current autocorrelation function [13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Size effect and transient phonon transport mechanism in approach-to-equilibrium molecular dynamics simulations

Sheng

Fan

et al. 2022

Phys. Rev. B

Self Cite

View full text Add to dashboard Cite

Approach-to-equilibrium molecular dynamics (AEMD) is a widely used molecular dynamics (MD) method to extract thermal transport properties in different material systems. Despite the success in many applications, the thermal transport mechanism in AEMD is not well understood. Although AEMD can simulate larger domain than other MD variants, it still suffers from simulation domain size effect. In addition, the size effect is quite different from that of the nonequilibrium molecular dynamics (NEMD) simulations. In this paper, we reveal the phonon transport mechanism in AEMD by comparing the size-dependent thermal conductivity values of AEMD and phonon Boltzmann transport equation. We show that the simulation size of AEMD should be defined as half of the size in the conventional AEMD simulations with periodic boundary conditions. Also, the size effect in AEMD originates from ballistic phonon transport. Different from NEMD, some phonons with long mean-free paths do not contribute to the thermal conductivity, resulting in a smaller thermal conductivity than NEMD with the same size. Based on the phonon transport mechanism in AEMD, we suggest an extrapolation method for AEMD to obtain bulk thermal conductivity.

show abstract

A Facile Strategy to Densify Aligned CNT Films with Significantly Enhanced Thermal Conductivity and Mechanical Strength

Liang

et al. 2022

Adv Materials Technologies

View full text Add to dashboard Cite

conductivity as a single assessment indicator for thermal management materials, often with simultaneous requirements for mechanical and other properties. Thus, carbon nanotubes (CNTs) possess outstanding thermal conductivity, satisfactory mechanical strength, and good chemical stability, which share huge potential in thermal management especially after the CNT fibers with higher tensile strength than any other fibers and ultralong length were reported. [2] In practical scenarios, mechanical traction of aligned CNT arrays followed by combining them into macroscopic aligned film is the main way for applying the superior performance of CNTs so that they can perform expected heat conduction. However, macroscopic CNT bodies normally exhibit dramatically reduced thermal conductivity and mechanical strength due to the low stacking density and unsatisfactory alignment of individual CNTs. [3] The degradation of thermal performance is mainly due to the weak van der Waals forces between the neighboring CNTs which originates from the preparation process of CNT films. [4] Meanwhile, the weak interfacial bonding also affects the effective transfer of loads among CNTs, resulting in comparatively poor mechanical strength. Researchers have achieved some progress on CNT densification, with the main ideas to introduce covalent bonds among CNTs via chemical cross-linking or to enhance the van der Waals forces by shortening the distance between the neighboring CNTs via external forces. [2b,5] Chemical cross-linking is the most effective method for densifying CNT films, but this method suffers from difficult operation, strict reaction conditions and high cost in large-scale treatment. In some cases, the introduction of polymer cross-linkers can also seriously affect the thermal conductivity of CNT films. In contrast, densification via liquid capillary forces or mechanical external forces is simple, mild, and more suitable for commercial and large-area treatment, that is, liquid infiltration and subsequent densification, [5a,b] and mechanical densification, [5c,d] in which the enhancement of performance relies on denser stacking and enhanced inter-tube interaction of CNTs rather than polymer adhesive. Previous studies normally apply a single means of densification, or involve time-consuming and Aligned carbon nanotube (CNT) films with outstanding thermal and mechanical properties are promising for thermal management in electronics and mechanical enhancement in composites. One main challenge toward aligned CNT films is the loose stacking and unsatisfactory orientation of individual CNTs within the macroscopic assemblies, resulting in unsatisfactory performance. In this study, a facile strategy to densify commercial aligned CNT films with nearly doubled stacking density increasing from 0.63 to 1.17 g•cm −3 , where the densification process involves infiltration of ethanol, CNT protonation along with mechanical stretching, is proposed. The densification strategy makes CNTs compactly aligned at the macro level, and enables CNTs to ...

show abstract

Interpretation of apparent thermal conductivity in finite systems from equilibrium molecular dynamics simulations

Cited by 13 publications

References 34 publications

Exactly equivalent thermal conductivity in finite systems from equilibrium and nonequilibrium molecular dynamics simulations

Exactly equivalent thermal conductivity in finite systems from equilibrium and nonequilibrium molecular dynamics simulations

Size effect and transient phonon transport mechanism in approach-to-equilibrium molecular dynamics simulations

A Facile Strategy to Densify Aligned CNT Films with Significantly Enhanced Thermal Conductivity and Mechanical Strength

Contact Info

Product

Resources

About