Confined fluid density of a pentaerythritol tetraheptanoate lubricant investigated using molecular dynamics simulation

2015 ◽  
Vol 385 ◽  
pp. 212-218 ◽  
Author(s):  
Ling Pan ◽  
Chenghui Gao
Author(s):  
Y-Z Hu ◽  
H Wang ◽  
Y Guo ◽  
L-Q Zheng

Molecular dynamics simulation has been performed in the present study for a Lennard-Jones (LJ) fluid in Poiseuille flow to examine the Theological behaviour of ultra-thin lubricating films. The results show that as two solid walls continuously approach each other, the effective viscosity of the confined fluid increases and goes towards divergence; the critical pressure of the phase transition declines as the film thickness reduces; when the separation exceeds ten molecular layers, however, the pressure curve slopes gently and tends to an asymptotic value-the bulk transition pressure of the lubricant; and an in-plane ordering structure will develop in the film, which originates from the wall-fluid interface and grows towards the middle of the film as the system pressure increases. It is concluded that the rheological performance of the lubricant may become film thickness dependent and a solid-liquid transition may be induced when the film is molecularly thin.


Author(s):  
Masoud Darbandi ◽  
Hossein Reza Abbasi ◽  
Rasoul Khaledi-Alidusti ◽  
Moslem Sabouri ◽  
Gerry E. Schneider

We use three-dimensional molecular dynamics simulation to investigate the driven flow between two parallel plates separated by argon atoms. Our simulations show that fluids in such channels can be continuously driven. Difference in surface wettability can cause a difference in fluid density along the nano channel. To control the nanochannel temperature walls, we use the thermal wall idea, which models the walls using atoms connected to their original positions by enforcing linear spring forces. In this study, we propose a nanochannel system in which, half of the channel has a low surface wettability, while the other half has a higher surface wettability and that the middle part of channel wall has a high temperature. In another test case, we study a channel with a high temperature at one side of channel and impose a low temperature at the other side. Imposing a high temperature at the middle of nanochannel breaks the molecular force balances and a driven flow is formed in the channel due to the difference in fluid density. Also, imposing a temperature gradient at the walls causes a momentum difference between the atoms on the opposite sides of channel, which is a reason for driving flow through the channel. We use these molecular dynamics tools to achieve better volumetric results in the nanochannel.


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