scholarly journals Heat current anticorrelation effects leading to thermal conductivity reduction in nanoporous Si

2020 ◽  
Vol 102 (20) ◽  
Author(s):  
Laura de Sousa Oliveira ◽  
S. Aria Hosseini ◽  
Alex Greaney ◽  
Neophytos Neophytou
Keyword(s):  
Thermal Conductivity ◽  
Heat Current ◽  
Nanoporous Si

Calculation of Thermal Conductivity in Nanofluids From Atomic-Scale Simulations

2005 ◽  
Author(s):  
Xuan Wu ◽  
Ranganathan Kumar ◽  
Parveen Sachdeva
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Pure Water ◽  
Research Work ◽  
Atomic Scale ◽  
Heat Current ◽  
Transfer Enhancement ◽  
Atomic Interactions ◽  
Time Autocorrelation Function

Nanofluids that consist of nanometer sized particles and fibers dispersed in base liquids have shown the potential to enhance the heat transfer performance. Although three features of nanofluids including anomalously high thermal conductivities at very low nanoparticle concentrations, strongly temperature dependent thermal conductivity and significant increases in critical heat flux have been studied widely, and layering of liquid molecules at the particle-liquid interface, ballistic nature of heat transport in nanoparticles, and nanoparticle clustering are considered as the possible causations responsible for such kind of heat transfer enhancement, few research work from atomic-scale has been done to verify or explain those fascinating features of nanofluids. In this paper, a molecular dynamic model, which incorporates the atomic interactions for silica by BKS potential with a SPC/E model for water, has been established. To ensure the authenticity of our model, the position of each atom in the nanoparticle is derived by the crystallographic method. The interfacial interactions between the nanoparticle and water are simplified as the sum of interaction between many ions. Due to the electrostatic interaction, the ions on the nanoparticle’s surface can attract a certain number of water molecules, therefore, the effect of interaction between the nanoparticle and water on heat transfer enhancement in nanofluids is studied. By using Green-Kubo equations which set a bridge between thermal conductivity and time autocorrelation function of the heat current, a model which may derive thermal conductivity of dilute nanofluids that consist of silica nanoparticles and pure water is built. Several simulation results have been provided which can reveal the possible mechanism of heat enhancement in nanofluids.

Thermal Conductivity of Individual Single-Wall Carbon Nanotubes

2006 ◽  
Vol 129 (6) ◽  
pp. 705-716 ◽  
Author(s):  
Jennifer R. Lukes ◽  
Hongliang Zhong
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Dynamics Simulation ◽  
Single Wall Carbon Nanotubes ◽  
Heat Current ◽  
Single Wall Carbon ◽  
Simulation Methodology

Despite the significant amount of research on carbon nanotubes, the thermal conductivity of individual single-wall carbon nanotubes has not been well established. To date only a few groups have reported experimental data for these molecules. Existing molecular dynamics simulation results range from several hundred to 6600 W∕m K and existing theoretical predictions range from several dozens to 9500 W∕m K. To clarify the several-order-of-magnitude discrepancy in the literature, this paper utilizes molecular dynamics simulation to systematically examine the thermal conductivity of several individual (10, 10) single-wall carbon nanotubes as a function of length, temperature, boundary conditions and molecular dynamics simulation methodology. Nanotube lengths ranging from 5 nm to 40 nm are investigated. The results indicate that thermal conductivity increases with nanotube length, varying from about 10 W∕m to 375 W∕m K depending on the various simulation conditions. Phonon decay times on the order of hundreds of fs are computed. These times increase linearly with length, indicating ballistic transport in the nanotubes. A simple estimate of speed of sound, which does not require involved calculation of dispersion relations, is presented based on the heat current autocorrelation decay. Agreement with the majority of theoretical/computational literature thermal conductivity data is achieved for the nanotube lengths treated here. Discrepancies in thermal conductivity magnitude with experimental data are primarily attributed to length effects, although simulation methodology, stress, and intermolecular potential may also play a role. Quantum correction of the calculated results reveals thermal conductivity temperature dependence in qualitative agreement with experimental data.

A Theoretical Approach to the Thermal Conductivity of Boron Carbides

1987 ◽  
Vol 97 ◽  
Author(s):  
V. M. Kenkre ◽  
X. Fan
Keyword(s):  
Thermal Conductivity ◽  
Model Calculation ◽  
Strong Interaction ◽  
Theoretical Approach ◽  
Vibrational Properties ◽  
Heat Current ◽  
Normal Behaviour ◽  
Partial Agreement ◽  
Fundamental Challenge ◽  
Increasing Temperature

ABSTRACTThe thermal conductivity of boron carbides at high temperatures presents a fundamental challenge to theory. One of the striking features is that, while in B4C it displays “normal” behaviour in that it decreases with increasing temperature, in B9C it is nearly temperature-independent. We address this feature through a model calculation which assumes the heat current to be due to carrier phonons whose frequency is modulated by lower-frequency phonons which “dress” the carrier phonons through strong interaction. Preliminary calculations show satisfactory but partial agreement with experiment for reasonable parameters and delineate areas for further investigation of the vibrational properties of boron carbides.

Molecular Dynamics Simulation of the Thermal Conductivity of Ar-Al Nanofluid Using Simplified Model

2009 ◽  
Author(s):  
Jie Liu ◽  
Wen-Qiang Lu
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Brownian Dynamics ◽  
Base Fluid ◽  
Numerical Results ◽  
Solid Particles ◽  
Dynamics Simulation ◽  
Simplified Model ◽  
Heat Current

Nanofluid is a colloidal solution of nano-sized solid particles in liquids. Ar-Al nanofluid is a promising heat transport fluid in the fields of low-temperature engineering. A simplified model based on the equilibrium molecular dynamics (EMD) simulation is constructed to calculate the thermal conductivity of argon suspension containing aluminum nanoparticles. The numerical method is verified by comparing the numerical results with the existing numerical results and the experimental data of the base fluid. The influence of various nanoparticle loadings is obtained and the results show that the thermal conductivity with 1% nanoparticle loading enhances up to 31% compared with the base fluid. The heat current autocorrelation functions converge well for the basefluid and nanofluid. Furthermore, interesting distinct oscillations are obtained especially at higher nanoparticle loading. The significant role of the interaction between the fluid atoms and the solid nanoparticle rather than Brownian dynamics motion of the nanoparticle in yielding the high thermal conductivity of nanofluid is numerically revealed.

scholarly journals Theoretical Evaluation of the Thermal Conductivity in Framework (Clathrate) Semiconductors

2000 ◽  
Vol 626 ◽  
Author(s):  
Jianjun Dong ◽  
Otto F. Sankey ◽  
Charles W. Myles ◽  
Ganesh K. Ramachandran ◽  
Paul F. McMillan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Correlation Function ◽  
Linear Response Theory ◽  
Heat Current ◽  
Theoretical Evaluation ◽  
Statistical Fluctuations ◽  
Current Correlation ◽  
Super Cell ◽  
Long Time ◽  
Auto Correlation Function

ABSTRACTWe have calculated the room temperature thermal conductivity in semiconductor germanium clathrates using statistical linear-response theory and an equilibrium molecular dynamics (MD) approach. A key step in our study is to compute a realistic heat-current J (t) and a corresponding auto-correlation function < J (t) J (0) >. To ensure convergence of our results and to minimize statistical fluctuations in our calculations, we have constructed large super-cell models (2944 atoms) and have performed several independent long time simulations (>1,500 ps in each simulation). Our results show an unexpected “oscillator” character in the heat-current correlation function of the guest-free Ge clathrate frameworks. This is absent in the denser diamond phase and other with simple structural frameworks. We seek to interpret these results using lattice dynamics information. A study of the effects of the so-called “rattling” guest atoms in the open-framework clathrate materials is in progress.

Lattice thermal conductivity of nanoporous Si: Molecular dynamics study

2007 ◽  
Vol 91 (22) ◽  
pp. 223110 ◽  
Author(s):  
J.-H. Lee ◽  
J. C. Grossman ◽  
J. Reed ◽  
G. Galli
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Lattice Thermal Conductivity ◽  
Nanoporous Si

Phonon Thermal Conductivity of the Cubic and Monoclinic Phases of Zirconia by Molecular Dynamics Simulation

2020 ◽  
Vol 843 ◽  
pp. 110-115
Author(s):  
Leila Momenzadeh ◽  
Irina V. Belova ◽  
Graeme E. Murch
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Lattice Thermal Conductivity ◽  
Dynamics Simulation ◽  
Heat Current ◽  
Phonon Thermal Conductivity ◽  
Low Thermal Conductivity ◽  
Two Phases

Zirconia has a number of remarkable properties, including a very low thermal conductivity. In this research, the phonon thermal conductivity of two phases (cubic and monoclinic) of zirconia (ZrO2) are calculated. For this purpose, an equilibrium molecular dynamics simulation employing the Green-Kubo formalism is used. The results are presented in detail over a wide temperature range, from 100 K to 2400 K and 100 K to 1400 K for the above-mentioned structures, respectively, with a 100K temperature step. The temperature dependence of the equilibrium atomic volume demonstrated a reasonable agreement with the experimental data. Moreover, the lattice thermal conductivity was calculated by analysing the heat current autocorrelation function. The results showed that zirconia has a low thermal conductivity that is dependent on the temperature. It was also shown that the lattice thermal conductivity of the two phases of zirconia can be decomposed into three contributions due to the acoustic shortrange and long-range phonon and optical phonon modes. Finally, the results from this research are compared with the available experimental data.

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