A Molecular Dynamics Study on Effects of Nanostructural Clearances at an Interface on Thermal Resistance

2008 ◽  
Author(s):  
Masahiko Shibahara ◽  
Kosuke Inoue ◽  
Kiyomori Kobayashi
Keyword(s):  
Molecular Dynamics ◽  
Temperature Gradient ◽  
Thermal Resistance ◽  
Solid Wall ◽  
Middle Layer ◽  
Dynamics Simulation ◽  
Nanometer Scale ◽  
Liquid Density ◽  
Solid Interface ◽  
Solid Walls

The classical molecular dynamics simulation was conducted in order to clarify the effects of structural clearances in nanometer scale on thermal resistance at a liquid-solid interface. A liquid molecular region confined between the solid walls, of which the interparticle potential was Lennard-Jones type, was employed as a calculation system. The solid walls consisted of three atomic layers where the temperature of the middle layer was controlled by the Langevin method. Heat flux in the system was calculated numerically by integrating the forces that acted on the temperature controlled atoms by the Langevin method. The temperature jump between the solid wall and the liquid molecular region was calculated numerically. The thermal resistance at a liquid-solid interface was calculated numerically with changing the surface structural clearances in nanometer scale. Temperature gradient and liquid density were also changed as calculation parameters. With changing the surface structural clearances from 0nm to 2.5nm the thermal resistance at the interface once decreased and became the minimum value when the structural clearances were between 0.6 to 1.0 nm. The thermal resistance between the solid and the liquid increased when the structural clearances were more than 1.0nm. With the increase of the liquid density the thermal resistance between the solid and the liquid substantially decreased regardless of the temperature gradient and the surface structures in nanometer scale.

A Molecular Dynamics Study on the Effects of Nanostructural Clearances on Thermal Resistance at a Liquid-Solid Interface

2009 ◽  
Author(s):  
Masahiko Shibahara ◽  
Kiyoshi Takeuchi
Keyword(s):  
Molecular Dynamics ◽  
Thermal Resistance ◽  
Surface Area ◽  
Solid Wall ◽  
Potential Parameter ◽  
Liquid Region ◽  
Solid Interface ◽  
Dynamics Simulations ◽  
Geometric Surface ◽  
Geometric Surface Area

The effects of the surface structures and the surface structural clearances at the nanometer scale on the thermal resistance at a liquid water-solid interface, as well as the dynamic behaviors of liquid molecules, were investigated directly by the classical molecular dynamics simulations. The thermal resistance between the solid wall and the liquid region was calculated by the temperature discontinuity at a liquid-solid interface and the energy flux that was added or subtracted by the Langevin method per unit area so as to maintain a constant solid wall temperature. When the potential parameter between liquid molecules and nanostructure atoms is equal to that between liquid molecules and solid wall atoms, the geometric surface area change depending on the nanostructures as well as their clearances and the dynamic behaviour change of the fluid molecules at the interface depending on the nanostructural clearances cause the thermal resistance reduction depending on the nanostructures at the liquid-solid interface. When the potential parameter between liquid molecules and nanostructure atoms is different from that between liquid molecules and solid wall atoms, the thermal resistance at the interface is dependent on the potential parameter between liquid molecules and nanostructure atoms rather than the geometric surface area in a molecular scale depending on the nanostructures as well as their clearances.

A Molecular Dynamics Study on the Effects of Nanostructural Clearances on Thermal Resistance at a Liquid-Solid Interface

2010 ◽  
Author(s):  
Masahiko Shibahara ◽  
Kiyoshi Takeuchi
Keyword(s):  
Molecular Dynamics ◽  
Thermal Resistance ◽  
Surface Area ◽  
Solid Wall ◽  
The Self ◽  
Potential Parameter ◽  
Self Diffusion ◽  
Solid Interface ◽  
Geometric Surface ◽  
Geometric Surface Area

The effects of the surface structures and the surface structural clearances at the nanometer scale on the thermal resistance at a liquid water-solid interface, as well as the self-diffusion behaviors of liquid molecules, were investigated directly by the non-equilibrium classical molecular dynamics simulations. When the potential parameter between liquid molecules and nanostructure atoms is equal to that between liquid molecules and solid wall atoms, the geometric surface area change depending on the nanostructures as well as their clearances and the self-diffusion coefficient change of the liquid molecules at the interface depending on the nanostructural clearances cause the thermal resistance change depending on the nanostructures at the liquid-solid interface. When the potential parameter between liquid molecules and nanostructure atoms is different from that between liquid molecules and solid wall atoms, the interfacial thermal resistance is dependent on the potential parameter between liquid molecules and nanostructure atoms itself rather than the geometric surface area in a molecular scale.

A Molecular Dynamics Study on Effects of Nanostructural Clearances on Thermal Resistance at an Interface Between Liquid and Solid

2008 ◽  
Author(s):  
Masahiko Shibahara ◽  
Kiyoshi Takeuchi
Keyword(s):  
Molecular Dynamics ◽  
Thermal Resistance ◽  
Surface Area ◽  
Resistance Index ◽  
Dynamics Simulation ◽  
Fluid Density ◽  
Resistance Change ◽  
Molecular Scale ◽  
Dynamics Simulations ◽  
Solid Walls

The classical molecular dynamics simulation was conducted in order to clarify the effects of the surface structural clearances in nanometer scale on thermal resistance at a liquid-solid interface as well as static and dynamic behaviours of fluid molecules in the vicinity of the surface. A liquid molecular region confined between the solid walls, of which the interparticle potential was Lennard-Jones type, was employed as a calculation system. The thermal resistance between the liquid molecular region and the solid walls with nanostructures was calculated by the heat flux and the temperature jump obtained in the molecular dynamics simulations. With changing the surface structural clearances from 0 to 2.81 nm the thermal resistance between the liquid molecular region and the solid walls with nanostructures once decreased and became the minimum value when the structural clearances were about 0.7 nm. Surface area in molecular scale and fluid density at the interface were dependent on the surface structural clearances and the thermal resistance index calculated by the relative surface area in molecular scale and the relative fluid density at the interface could predict thermal resistance change depending on the nanostructural clearances. Surface nanostructural clearances affected the fluid molecular motions along the heat transfer direction only when the molecular velocity was averaged over a specific characteristic time. Surface nanostructural clearances affected the diffusion behaviours of fluid molecules in the vicinity of the surface too.

Multiscale flow characteristics of droplet spreading with microgravity conditions

2019 ◽  
Vol 97 (8) ◽  
pp. 869-874
Author(s):  
Xue-Qing Chen ◽  
Lei Tong
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Solid Wall ◽  
Gold Surface ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Contact Radius ◽  
Droplet Spreading ◽  
Fast Spreading ◽  
Slow Spreading

In this paper, mesoscopic lattice–Boltzmann method (LBM) and microscopic molecular dynamics simulation method were used to simulate droplet dynamic wetting under microgravity. In terms of LBM, the wetting process of a droplet on a solid wall surface was simulated by introducing the fluid–fluid and solid–fluid interactions. In terms of molecular dynamics simulation, the spreading process of water on gold surface was simulated. Calculation results showed that two kinds of calculation methods were based on the microscopic molecular theory or mesoscopic kinetics theory, and such models could effectively overcome the contact line paradox issue, which results from the macro-continuum assumption and non-slip boundary condition assumption. The spreading exhibits two-stage behavior: fast spreading and slow spreading stages. For the two simulation methods, the ratio of fast spreading stage duration to slow spreading duration, spreading capacity (equilibrium contact radius/initial radius), and the spreading exponent of the rapid stage were very close. However, the predictive spreading index of the slow spreading stage was different, owing to the different spreading mechanisms between meso- and nanoscales.

Molecular Dynamics Simulation of Homogeneous and Heterogeneous Thermal Bubble Nucleation

2011 ◽  
Author(s):  
Min Chen ◽  
Yunfei Chen ◽  
Juekuan Yang ◽  
Yandong Gao ◽  
Deyu Li
Keyword(s):  
Molecular Dynamics ◽  
Heterogeneous Systems ◽  
Liquid Argon ◽  
Bubble Nucleation ◽  
Dynamics Simulation ◽  
Nucleation Temperature ◽  
The Common ◽  
Solid Walls ◽  
Common Understanding ◽  
Superheat Limit

Thermal bubble nucleation was studied using molecular dynamics for both homogeneous and heterogeneous systems using isothermal-isobaric (NPT) and isothermal-isostress (NPzzT) ensembles. Simulation results indicate that homogeneous thermal bubble nucleation is induced from cavities occurring spontaneously in the liquid when the temperature exceeds the superheat limit. In contrast to published results using NVE and NVT ensembles, no stable nanoscale bubble exists in NPT ensembles, but instead, the whole system changes into vapor phase. For a heterogeneous system composed of a nanochannel with an initial distance of 3.49 nm between the two solid plates, it is found that if the liquid-solid interaction is equal to or stronger than that between liquid argon atoms, the bubble nucleation temperature of the confined liquid argon can be higher than the corresponding homogeneous nucleation temperature, because of the more ordered arrangement of atoms within two solid walls nanometers apart. This observation is in contradiction to the common understanding that homogeneous bubble nucleation temperature sets an upper limit for thermal phase change under a given pressure. Compared to the system where the liquid-solid interaction is the same as that between liquid argon atoms, the system with reduced liquid-solid interaction possesses a significantly reduced bubble nucleation temperature, while the system with enhanced liquid-solid interaction only has a marginally increased bubble nucleation temperature.

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