scholarly journals Equilibrium Molecular Dynamics Study of Lattice Thermal Conductivity/Conductance of Au-SAM-Au Junctions

2009 ◽  
Vol 132 (3) ◽  
Author(s):  
Tengfei Luo ◽  
John R. Lloyd
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Thermal Energy ◽  
Energy Transport ◽  
Thermal Conductance ◽  
Finite Size ◽  
Thickness Effect ◽  
Finite Size Effect ◽  
Substrate Thickness ◽  
Thermal Energy Transport

In this paper, equilibrium molecular dynamics simulations were performed on Au-SAM (self-assembly monolayer)-Au junctions. The SAM consisted of alkanedithiol (–S–(CH2)n–S–) molecules. The out-of-plane (z-direction) thermal conductance and in-plane (x- and y-direction) thermal conductivities were calculated. The simulation finite size effect, gold substrate thickness effect, temperature effect, normal pressure effect, molecule chain length effect, and molecule coverage effect on thermal conductivity/conductance were studied. Vibration power spectra of gold atoms in the substrate and sulfur atoms in the SAM were calculated, and vibration coupling of these two parts was analyzed. The calculated thermal conductance values of Au-SAM-Au junctions are in the range of experimental data on metal-nonmetal junctions. The temperature dependence of thermal conductance has a similar trend to experimental observations. It is concluded that the Au-SAM interface resistance dominates thermal energy transport across the junction, while the substrate is the dominant media in which in-plane thermal energy transport happens.

scholarly journals Molecular dynamics simulation of thermal energy transport in polydimethylsiloxane

2011 ◽  
Vol 109 (7) ◽  
pp. 074321 ◽  
Author(s):  
Tengfei Luo ◽  
Keivan Esfarjani ◽  
Junichiro Shiomi ◽  
Asegun Henry ◽  
Gang Chen
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Thermal Energy ◽  
Energy Transport ◽  
Dynamics Simulation ◽  
Thermal Energy Transport

Physical Mechanisms of Thermal Transport in Nanofluids

2011 ◽  
Author(s):  
John Shelton ◽  
Frank Pyrtle
Keyword(s):  
Thermal Conductivity ◽  
Thermal Energy ◽  
Energy Exchange ◽  
System Analysis ◽  
Energy Transport ◽  
Physical Mechanism ◽  
Conductivity Enhancement ◽  
Physical Mechanisms ◽  
Dynamics Simulations ◽  
Thermal Energy Transport

Using molecular dynamics simulations, an analysis of the thermal conductivity enhancement of a copper/argon nanofluid is performed. First, verification of an increase of as much as ∼30% in the thermal conductivity of the theoretical nanofluid over the corresponding base fluid, due to increasing nanoparticle concentration, is presented. Thermal energy transport is then decomposed into potential, kinetic, and virial components, based on the Green-Kubo autocorrelation function used to calculate thermal conductivity from the microscopic properties of the system. Analysis of these components showed that as the concentration of the nanoparticle increases, the energy transported through the system, due to collisions within the fluid, decreases by as much as 80%. Additionally, the nanofluid system increasingly displays characteristics of an amorphous-like material with increasing concentration. The decrease in energy exchange, due to collisions, suggests another physical mechanism is present for thermal energy transport. Therefore, it is proposed that thermal diffusion is the physical mechanism that more significantly affects thermal energy transport within a nanofluid than had been previously suggested.

Thin Film Phonon Heat Conduction by the Dispersion Lattice Boltzmann Method

2007 ◽  
Author(s):  
Rodrigo A. Escobar ◽  
Cristina H. Amon ◽  
Amador M. Guzma´n
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Lattice Boltzmann Method ◽  
Thermal Energy ◽  
Lattice Boltzmann ◽  
Energy Transport ◽  
Time Dependent ◽  
Boltzmann Method ◽  
Thermal Energy Transport

Numerical simulations of time-dependent thermal energy transport in semiconductor thin films are performed using the Lattice Boltzmann Method applied to phonon transport. The discrete Lattice Boltzmann Method is derived from the continuous Boltzmann transport equation assuming nonlinear, frequency-dependent phonon dispersion for acoustic and optical phonons. Results indicate that the heat conduction in silicon thin films displays a transition from diffusive to ballistic energy transport as the characteristic length of the system becomes comparable to the phonon mean free path, and that the thermal energy transport process is characterized by the propagation of multiple, superimposed phonon waves. The methodology is used to characterize the time-dependent temperature profiles inside films of decreasing thickness. Thickness-dependent thermal conductivity values are computed based on steady-state temperature distributions obtained from the numerical models. It is found that reducing feature size into the subcontinuum regime decreases the thermal conductivity when compared to bulk values, at a higher rate than what was displayed by the Debye-based gray Lattice Boltzmann Method.

Ab Initio Molecular Dynamics Study of Nanoscale Thermal Energy Transport

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Tengfei Luo ◽  
John R. Lloyd
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Thermal Energy ◽  
Density Functional ◽  
Energy Transport ◽  
Power Spectra ◽  
Ab Initio Molecular Dynamics ◽  
Nanoscale Structures ◽  
Different Temperatures ◽  
Thermal Energy Transport

Ab initio molecular dynamics, which employs density functional theory, is used to study thermal energy transport phenomena in nanoscale structures. Thermal equilibration in multiple thin layer structures with thicknesses less than 1 nm per layer is simulated. Different types of layer combinations are investigated. Periodic boundary conditions in all directions are used in all cases. Two neighboring layers are first set to different temperatures using Nosé–Hoover thermostats, and then the process of energy equilibration is simulated with a “free run” (without any thermostat controlling the temperatures). The temperature evolutions in the two neighboring layers are computed. The atomic vibration power spectra are calculated and used to explain the phenomena observed in the simulation.

Study of Thermal Energy Transport Between Hydrogen Gas Molecules and a Single-Wall Carbon Nanotube Using Molecular Dynamics Simulations

2005 ◽  
Author(s):  
Jose´ E. Solomon ◽  
Jay Kapat ◽  
Ranganathan Kumar ◽  
Deepak Srivastava
Keyword(s):  
Molecular Dynamics ◽  
Energy Transfer ◽  
Carbon Nanotube ◽  
Thermal Energy ◽  
Energy Transport ◽  
Md Simulations ◽  
Hydrogen Gas ◽  
Gas Density ◽  
Gas Molecules ◽  
Thermal Energy Transport

The focus of the current research is the investigation and characterization of the energy transport between a (10,10) single-wall carbon nanotube (SWCNT) and surrounding molecular hydrogen gas using molecular dynamics (MD) simulations. The MD simulations use Tersoff-Brenner hydrocarbon potential for C-C, C-H, and H-H bonding interactions and the conventional Lennard-Jones potential for soft-sphere gas-CNT collision dynamics of H-H and H-C non-bonding van der Waals interactions. A simulation cell with periodic boundary conditions is created for 1200 carbon atoms in an armchair nanotube configuration and three distinct gas densities corresponding to 252, 500, and 1000 H2 molecules in the same volume. The MD simulation runs are performed with time steps of 0.1 fs and the total simulation times of 40 ps. The simulations are initialized by setting the gas species and CNT at two different temperatures. Initial gas temperatures range from 2000K to 4000K, whereas the carbon nanotube is held at 300K. After the equilibrium temperatures of the CNT and the gas molecules are achieved, the external constraints to maintain the temperature are removed and the thermal energy transport between the two is studied. The kinetic energy exchange between the nanotube and the surrounding gas is monitored to study thermal energy transport over the duration of the simulation. A parameter is proposed, the coefficient of thermal energy transfer (CTET), to characterize the thermal transport properties of the modeled systems based on parameters governing the transport process, thus mimicking the conventional heat transfer coefficient. Values for CTET vary directly with gas density and range from 50 MW/m2K to 250MW/m2K, showing that gas density has a significant impact with higher density corresponding to higher collision rates and higher rates of energy transfer. In contrast, the gas temperature has a lower impact on CTET, with colder gas providing in certain cases a slightly lower value for the coefficient. In order to validate the MD simulations, the time-series data of molecular vibrations of the CNT is converted to a vibrational frequency spectrum through FFT. The characteristic frequencies obtained on the spectra of isolated SWCNT and H2 simulations are compared against the known natural frequencies of the CNT phonon modes and vibrational modes of H2 molecules. The comparison is quite favorable.

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