Study of gaseous velocity slip in nano-channel using molecular dynamics simulation

2014 ◽  
Vol 24 (6) ◽  
pp. 1338-1347 ◽  
Author(s):  
Fubing Bao ◽  
Zhihong Mao ◽  
Limin Qiu
Keyword(s):  
Molecular Dynamics ◽  
Gas Flow ◽  
Interaction Strength ◽  
Flow Characteristics ◽  
Velocity Slip ◽  
Dynamics Simulation ◽  
Wall Region ◽  
Content Type ◽  
Slip Phenomenon ◽  
Near Wall

Purpose – The purpose of this paper is to investigate the gas flow characteristics in near wall region and the velocity slip phenomenon on the wall in nano-channels based on the molecular dynamics simulation. Design/methodology/approach – An external gravity force was employed to drive the flow. The density and velocity profiles across the channel, and the velocity slip on the wall were studied, considering different gas temperatures and gas-solid interaction strengths. Findings – The simulation results demonstrate that a single layer of gas molecules is adsorbed on wall surface. The density of adsorption layer increases with the decrease of gas temperature and with increase of interaction strength. The near wall region extents several molecular diameters away from the wall. The density profile is flatter at higher temperature and the velocity profile has the traditional parabolic shape. The velocity slip on the wall increases with the increase of temperature and with decrease of interaction strength linearly. The average velocity decreases with the increase of gas-solid interaction strength. Originality/value – This research presents gas flow characteristics in near wall region and the velocity slip phenomenon on the wall in nano-channels. Some interesting results in nano-scale channels are obtained.

scholarly journals Molecular Dynamics Simulation of Nanoscale Channel Flows with Rough Wall Using the Virtual-Wall Model

2018 ◽  
Vol 2018 ◽  
pp. 1-7
Author(s):  
Xiaohui Lin ◽  
Fu-bing Bao ◽  
Xiaoyan Gao ◽  
Jiemin Chen
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Gas Flow ◽  
Roughness Element ◽  
Fluid Velocity ◽  
Flow Characteristics ◽  
Rough Wall ◽  
Dynamics Simulation ◽  
Low Density ◽  
Wall Model

Molecular dynamics simulation is adopted in the present study to investigate the nanoscale gas flow characteristics in rough channels. The virtual-wall model for the rough wall is proposed and validated. The computational efficiency can be improved greatly by using this model, especially for the low-density gas flow in nanoscale channels. The effect of roughness element geometry on flow behaviors is then studied in detail. The fluid velocity decreases with the increase of roughness element height, while it increases with the increases of element width and spacing.

Vapor Embryo Nucleation in Near-Wall Region Under Pool Boiling Conditions

2010 ◽  
Author(s):  
Bofeng Bai ◽  
Sijie Li
Keyword(s):  
Solid Wall ◽  
Pool Boiling ◽  
Interaction Strength ◽  
Simulation System ◽  
Dynamics Simulation ◽  
Bulk Liquid ◽  
Wall Region ◽  
Liquid Region ◽  
Simulation Results ◽  
Near Wall

To construct a model of the microscopic near-wall region in a macroscopic pool boiling system, the present work introduced the effect of the solid wall at the bottom of the simulation system and the infinite liquid region outside it as extra potential. Molecular dynamics simulation results showed that thermodynamics properties of near-wall region was influenced by the interaction strength and deviated from the bulk liquid region. Vapor embryo nucleated at a position several nanometers away from the solid surface. With the increase of Hamaker constant, the vapor embryo occurred at a position farther away from the solid wall.

THE "FOLDING" BEHAVIORS OF HOMOPOLYMERS WITH ONE END FIXED

2004 ◽  
Vol 18 (15) ◽  
pp. 2123-2139 ◽  
Author(s):  
BIN XUE ◽  
JUN WANG ◽  
WEI WANG
Keyword(s):  
Molecular Dynamics ◽  
Chain Length ◽  
Conformational Changes ◽  
Canonical Ensemble ◽  
Interaction Strength ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Radius Of Gyration ◽  
Native Conformation ◽  
Collapse Temperature

We study the "folding" behaviors of homopolymers with one end fixed. By using canonical ensemble molecular dynamics simulation method, we observe the conformational changes during folding processes. Long chains collapse to the helical nuclei, then regroup to helix from the free-end to form the compact conformations through the middle stages of helix-like coil and helix-like cone, while short chains do not apparently have the above mentioned middle stages. Through simulated annealing, the native conformation of homopolymer chain in our model is found to be helix. We show the relations between specific heat C v (T) and radius of gyration R g (T) as functions of temperature, chain length and the interaction strength, respectively. We find that these two quantities match well and can be combined to interpret the "folding" process of the homopolymer. It is found that the collapse temperature Tθ and the native-like folding temperature T f do not change with the chain length in our model, however the interaction strength affects the values of Tθ and T f .

scholarly journals Event-Driven Molecular Dynamics Simulation of Hard-Sphere Gas Flows in Microchannels

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Volkan Ramazan Akkaya ◽  
Ilyas Kandemir
Keyword(s):  
Molecular Dynamics ◽  
Hard Sphere ◽  
Stokes Equations ◽  
Hard Spheres ◽  
Flow Characteristics ◽  
Dynamics Simulation ◽  
Navier Stokes ◽  
Gas Flows ◽  
Linearized Boltzmann Equation ◽  
Event Driven

Classical solution of Navier-Stokes equations with nonslip boundary condition leads to inaccurate predictions of flow characteristics of rarefied gases confined in micro/nanochannels. Therefore, molecular interaction based simulations are often used to properly express velocity and temperature slips at high Knudsen numbers (Kn) seen at dilute gases or narrow channels. In this study, an event-driven molecular dynamics (EDMD) simulation is proposed to estimate properties of hard-sphere gas flows. Considering molecules as hard-spheres, trajectories of the molecules, collision partners, corresponding interaction times, and postcollision velocities are computed deterministically using discrete interaction potentials. On the other hand, boundary interactions are handled stochastically. Added to that, in order to create a pressure gradient along the channel, an implicit treatment for flow boundaries is adapted for EDMD simulations. Shear-Driven (Couette) and Pressure-Driven flows for various channel configurations are simulated to demonstrate the validity of suggested treatment. Results agree well with DSMC method and solution of linearized Boltzmann equation. At low Kn, EDMD produces similar velocity profiles with Navier-Stokes (N-S) equations and slip boundary conditions, but as Kn increases, N-S slip models overestimate slip velocities.

scholarly journals Hybrid atomistic-continuum multiscale method for fluid flow with density variation in microchannels

2018 ◽  
Vol 28 (1) ◽  
pp. 3-30 ◽  
Author(s):  
Van Huyen Vu ◽  
Benoît Trouette ◽  
Quy Dong TO ◽  
Eric Chénier
Keyword(s):  
Hybrid Method ◽  
Large Scale ◽  
Gas Flow ◽  
Velocity Slip ◽  
Cost Effective ◽  
Density Variation ◽  
Multiscale Method ◽  
Navier Stokes ◽  
Content Type ◽  
Energy Equations

Purpose This paper aims to extend the hybrid atomistic-continuum multiscale method developed by Vu et al. (2016) to study the gas flow problems in long microchannels involving density variations. Design/methodology/approach The simulation domain is decomposed into three regions: the bulk where the continuous Navier–Stokes and energy equations are solved, the neighbourhood of the wall simulated by molecular dynamics and the overlap region which connects the macroscopic variables (density, velocity and temperature) between the two former regions. For the simulation of long micro/nanochannels, a strategy with multiple molecular blocks all along the fluid/solid interface is adopted to capture accurately the macroscopic velocity and temperature variations. Findings The validity of the hybrid method is shown by comparisons with a simplified analytical model in the molecular region. Applications to compressible and condensation problems are also presented, and the results are discussed. Originality/value The hybrid method proposed in this paper allows cost-effective computer simulations of large-scale problems with an accurate modelling of the transfers at small scales (velocity slip, temperature jump, thin condensation films, etc.).

EFFECTS OF HYDROPHOBIC SURFACE NANOBUBBLES ON THE FLOW IN NANOCHANNELS

2011 ◽  
Vol 25 (10) ◽  
pp. 773-780 ◽  
Author(s):  
HUI XIE ◽  
CHAO LIU
Keyword(s):  
Molecular Dynamics ◽  
Fluid Flow ◽  
Molecular Dynamics Simulation ◽  
Velocity Slip ◽  
Hydrophobic Surface ◽  
Dynamics Simulation ◽  
Attractive Force

It has been demonstrated that there are nanobubbles on hydrophobic surface. Molecular dynamics simulation was adopted to investigate the impacts of the hydrophobic surface nanobubbles on fluid flow in nanochannel. A method for calculating the velocity of nanobubbles is presented. The results show that the bubbles on two plates enhance the velocity slip and disturb the flow. The behavior is attributed to the attractive force between nanobubbles.

Molecular Dynamics Simulation on the Effect of Micro-Motions of Nanoparticles in Heat Transfer Enhancement of Nanofluids

2016 ◽  
Author(s):  
Chengzhi Hu ◽  
Minli Bai ◽  
Jizu Lv ◽  
Yuyan Wang
Keyword(s):  
Heat Transfer ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Shear Flow ◽  
Flow Field ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Dynamics Simulation ◽  
Wall Region ◽  
Transfer Enhancement

The flow and heat transfer characteristics of nanofluids in the near-wall region were studied by non-equilibrium molecular dynamics simulation. The nanofluid model consisted of one spherical copper nanoparticle and argon atoms as base liquid. The effective thermal conductivity (ETC) of nanofluids and base fluid in shear flow fields were obtained. The ETC was increased with the increasing of shear velocity for both base fluid and nanofluids. The heat transfer enhancement of nanofluids in the shear flow field (v≠0) is better than that in the zero-shear flow field (v=0). By analyzing the flow characteristics we proved that the micro-motions of nanoparticles were another mechanism responsible for the heat transfer enhancement of nanofluids in the flow field. Based on the model built in the paper, we found that the thermal properties accounted for 52%–65% heat transfer enhancement and the contribution of micro-motions is 35%–48%.

scholarly journals On the Microscopic Flow Characteristics of Nanofluids by Molecular Dynamics Simulation on Couette Flow

2012 ◽  
Vol 5 (1) ◽  
pp. 21-27 ◽  
Author(s):  
Wenzheng Cui ◽  
Minli Bai ◽  
Jizu Lv ◽  
Xiaojie Li
Keyword(s):  
Heat Transfer ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Heat Transfer Enhancement ◽  
Couette Flow ◽  
Flow Characteristics ◽  
Dynamics Simulation ◽  
Shear Direction ◽  
Transfer Enhancement ◽  
Microscopic Flow

Adding a small amount of nanoparticles to conventional fluids (nanofluids) has been proved to be an effective way for improving capability of heat transferring in base fluids. The change in micro structure of base fluids and micro motion of nanoparticles may be key factors for heat transfer enhancement of nanofluids. Therefore, it is essential to examine these mechanisms on microscopic level. The present work performed a Molecular Dynamics simulation on Couette flow of nanofluids and investigated the microscopic flow characteristics through visual observation and statistic analysis. It was found that the even-distributed liquid argon atoms near solid surfaces of nanoparticles could be seemed as a reform to base liquid and had contributed to heat transfer enhancement. In the process of Couette flow, nanoparticles moved quickly in the shear direction accompanying with motions of rotation and vibration in the other two directions. When the shearing velocity was increased, the motions of nanoparticles were strengthened significantly. The motions of nanoparticles could disturb the continuity of fluid and strengthen partial flowing around nanoparticles, and further enhanced heat transferring in nanofluids.

Sign in / Sign up

Export Citation Format

Share Document