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Title: Heat transport in fluids and interfaces via non-equilibrium molecular dynamics simulations
Author: Muscatello, Jordan
ISNI:       0000 0004 2736 9342
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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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.
Supervisor: Bresme, Fernando Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral