In this thesis non-equilibrium molecular dynamics is used to investigate effects relating to thermal transport in fluids and interfacial systems.
Non-equilibrium molecular dynamics (NEMD) simulations of liquid water
were undertaken using the Modified Central Force model (MCFM) of
water. Non-equilibrium thermodynamics predicts dipolar alignment as a
response to an applied temperature gradient. This effect was systematically
investigated by applying thermal gradients of up to 4 K/ Å to a system of
MCFM water. This yielded induced electric fields of up to ~ 109 Vm-1.
The predictions of non-equilibrium thermodynamics were supported by the
simulations. The mechanism of thermal transport was investigated.
The effect of electrostatic interactions on the thermal transport properties
was also investigated in this model comparing the Ewald summation and
Wolf methods. It was found that whilst the change in equation of state
using each method is small, the truncation of the electrostatic interactions
leads to a lower heat flux density and values for the thermal conductivity
that are ~ 5 - 10% lower. The relaxation of the system to a steady-state
temperature gradient was also investigated and the timescales involved were
found to agree with the results using the macroscopic heat equation.
The hydrogen bonding contribution to the heat flux vector was investigated. This was found to contribute to around 30-40% of the total heat flux
for MCFM water. The potential energy contribution was found to become
negative towards lower temperatures. Also investigated was the thermal
conductivity of glassy water with the aim of identifying a difference in the
thermal conductivity from liquid to the glass state. The SPC/E model was
employed for this purpose but no significant change was identified.
NEMD simulations were employed to investigate the interfacial thermal
resistance of liquid/vapour and solid/vapour interfaces in a Lennard-Jones
system. For energy fluxes of ≈107 Wm-2 a significant interfacial thermal
resistance was observed, particularly at low temperatures. To investigate
the microscopic origin of the interfacial thermal resistance, the intrinsic
sampling method was employed in the liquid/vapour interface. The temperature
drop was found to occur in front of the interface in a region where
adsorbed atoms at the surface correspond to a density peak in the vapour
phase.