Molecular Dynamics Simulation of Heat Conduction in Si Thin Films Induced by Ultrafast Laser Heating

2012 ◽  
Author(s):  
Yu Zou ◽  
Xiulan Huai ◽  
Fang Xin ◽  
Zhixiong Guo
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Heat Conduction ◽  
Temperature Distribution ◽  
Laser Heating ◽  
Ultrafast Laser ◽  
Average Stress ◽  
Dynamics Simulation ◽  
Net Heat Flux ◽  
Si Films

Molecular dynamics simulations are carried out to study the thermal and mechanical phenomena of ultra-high heat flux conduction induced by ultrafast laser heating in thin Si films. Nanoscale Si films with various depths in heat flux direction are treated as a semi-infinite model for the study of ultrafast heat conduction. A distribution of internal heat source is applied to simulate the absorption of the laser energy in films and the induced temperature distribution. Stress distribution and the evolution of the displacement are calculated. Thermal waves are observed from the development of temperature distribution in the heat flux direction, though the average temperature of the simulated Si films increases monotonically. The average stress shows periodic oscillations. The time development of strain has the same trend as the average stress, and the net heat flux shows the same trend as the stress at different depths of the Si films in the direction of heat flux. This reveals a close relationship between stress and net heat flux in the Si films in the process of ultrafast laser heating.

Molecular Dynamics Simulation of the Evaporation and Transfer of the Lubricant on a Hard Disk in Heat-Assisted Magnetic Recording

2018 ◽  
Author(s):  
M. Ashraful Haq ◽  
Shao Wang ◽  
Zhencheng Ren ◽  
Yalin Dong
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Laser Heating ◽  
Periodic Boundary ◽  
Periodic Boundary Conditions ◽  
Disk Surface ◽  
Dynamics Simulation ◽  
Coarse Grained ◽  
Fresh Material ◽  
Novel Concept

Coarse-grained models were developed to study the evaporation and transfer of the perfluoropolyether lubricant from the disk surface under laser heating. Both moving and stationary disks were simulated with a heat flux applied to a central region under a pad. A novel concept of a reconditioning region was proposed to convert the periodic boundary conditions to more realistic conditions with the fresh material fed at the inlet. The results indicate significant influence of the disk velocity, heat flux and gap distance on the evaporation and transfer of the lubricant. With increasing heat flux, more lubricant molecules tend to reach the slider surface.

Heat Conduction Rectification in Nanostructure With Step Change in Cross-Section

2010 ◽  
Author(s):  
Xingang Liang ◽  
Bao Yue
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Thermal Resistance ◽  
Cross Section ◽  
Temperature Difference ◽  
Flow Direction ◽  
Step Change ◽  
Dynamics Simulation ◽  
Rectification Effect ◽  
Thick Part

Heat conduction rectifier is attracting more attention due to its potential application to process thermal currents independently and convert them into electronic signals. This work reports an investigation by molecular dynamics simulation on the heat conduction rectification effect in the nanostructure whose cross-section have step change along the heat flux. It is found that thermal resistance is different with reversed heat flux direction, which is called the heat conduction rectification. The heat conduction rectification depends on the temperature difference. By reducing temperature difference across the nanostructure, the rectification could be reversed. When the temperature difference is small enough, the thermal resistance is larger when the heat flux flows from the thick part to the thin part when the length of the structure is about 10 nm. The larger variation in the cross-section leads the larger difference in the thermal resistance with opposite heat flux. The mechanism of the rectification is discussed. If we take phonons as liquid particles and consider the case of a liquid flowing through a channel with step expansion in cross-section, the flow resistance is less with liquid flowing from the narrow part to the wide part than that in the case with contrary flow direction. In fact, the scattering of phonons at the step face reduces the mean free path of phonon when heat flux conducts from the narrow end to the wide end.

Molecular Dynamics Simulation for Homogenous Nucleation of Water and Liquid Nitrogen in Explosive Boiling

2009 ◽  
Author(s):  
Yu Zou ◽  
Xiulan Huai
Keyword(s):  
Molecular Dynamics ◽  
Energy Conversion ◽  
Liquid Nitrogen ◽  
Laser Heating ◽  
Equilibrium Temperature ◽  
Dynamics Simulation ◽  
Working Fluid ◽  
Heating Zone ◽  
Explosive Boiling ◽  
Heat Quantity

Molecular dynamics simulations are carried out to study the energy conversion in the homogeneous nucleation processes of the explosive boiling caused by laser heating. Liquid nitrogen and water are investigated as the working fluid. Velocity scaling method is applied to realize the laser heating process. Three influencing factors, the heat quantity into the system, the area of the laser heating zone and the initial equilibrium temperature of the liquid are analyzed. It is found that the conversion ratio of energy between heat quantity and potential energy is from 66% to 78% in the process of laser heating. The influence of the heat quantity into the system on the energy conversion of liquid nitrogen is the same in trend as that of water. The influence of the initial equilibrium temperature and the area of the laser heating zone on the liquid nitrogen is less than that of water. The difference of energy conversion between water and liquid nitrogen is pretty dramatic, which is because of the hydrogen bond formed by the Coulombic interaction among water molecules.

Nano Heat Pipe: Nonequilibrium Molecular Dynamics Simulation

2016 ◽  
Author(s):  
Mohammad Moulod ◽  
Gisuk Hwang
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Heat Pipe ◽  
Thermal Management ◽  
Operating Conditions ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
Management Systems ◽  
Working Fluid ◽  
Maximum Heat

A heat pipe has been known as a thermal superconductor utilizing a liquid-vapor phase change, and it has drawn significant attentions for advanced thermal management systems. However, a challenge is the size limitation, i.e., the heat pipe cannot be smaller than the evaporator/condenser wick structures, typically an order of micron, and a new operating mechanism is required to meet the needs for the nanoscale thermal management systems. In this study, we design the nanoscale heat pipe employing the gas-filled nanostructure, while transferring heat via ballistic fluid-particle motions with a possible returning working fluid via surface diffusions along the nanostructure. The enhanced heat flux for the nano heat pipe is demonstrated using the nonequilibrium molecular dynamics simulations (NEMDS) for the argon gas confined by the 20 nm-long Pt nanogap with a post wall with the temperature difference between the hot and cold surfaces of 20 K. The predicted results show that the maximum heat flux through the gas-filled nanostructure (heat pipe) nearly doubles that of the nanogap without the post wall at 100 < T < 140 K. The optimal operating conditions/material selections are discussed. The results for the nanogap agree with those obtained from the kinetic theory, and provide insights into the design of advanced thermal management systems.

Thermal Rectification in Silicon Nanowires With Mass Gradients

2008 ◽  
Author(s):  
Shuai-Chuang Wang ◽  
Xin-Gang Liang ◽  
Xiang-Hua Xu
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Molecular Dynamics Simulation ◽  
Silicon Nanowires ◽  
Dynamics Simulation ◽  
Effect Of Temperature ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Thermal Rectification ◽  
Axial Mass

Thermal rectification as a new phenomenon is attracting great attention. Thermal rectification in silicon nanowires with axial mass gradient is investigated by molecular dynamics simulation. The results of the simulations show that the thermal conductivities are different for the heat flux with opposite directions. The rectification efficiency becomes larger when the mass gradient increases. The effect of temperature gradient on the thermal rectification is also considered. The phonon density of states is calculated to explain the phenomenon. It is found that the interface is responsible to the thermal rectification.

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