THESIS
2013
iii leaves, 67 p. : ill. (some col.) ; 30 cm
Abstract
The dynamic behaviors of nanoscale confined fluids under temperature gradients can be different from that of bulk fluids. This is because temperature gradients and fluid-wall interaction play important roles in the nanoscale constricted fluids and can greatly affect fluid properties. In this work, molecular dynamic (MD) simulations are used to study nanoscale confined fluids under longitudinal and transverse temperature gradients and their possible applications in thermal systems....[
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The dynamic behaviors of nanoscale confined fluids under temperature gradients can be different from that of bulk fluids. This is because temperature gradients and fluid-wall interaction play important roles in the nanoscale constricted fluids and can greatly affect fluid properties. In this work, molecular dynamic (MD) simulations are used to study nanoscale confined fluids under longitudinal and transverse temperature gradients and their possible applications in thermal systems.
For a fluid confined by two parallel solid walls, it is found that the fluid moves when there is a temperature gradient along the wall. The flow direction depends on the strength of the fluid-wall interaction. For strong fluid-wall interactions, the fluid flows from low to high temperature due to the pressure variation caused by the coupling influence of temperature gradient and fluid-wall interactions. For weak fluid-wall interactions, however, the fluid migrates from high to low temperature, which is brought about by a potential ratchet near the solid surfaces. Moreover, the average flow velocity shows nonlinear dependence on the fluid-wall binding energy, ε
fw, and a maximum flow flux is found when ε
fw / kT
L ≈ 1, where k is the Boltzmann constant and T
L is the lower temperature of the temperature gradient. The possible applications for cooling electronic devices are discussed.
For a fluid confined by two parallel solid walls under a transversal temperature gradient, it is found that the thermal resistance of fluid depends on the direction of the temperature gradient. Consequently, the thermal resistance of the system becomes temperature gradient dependent and a relative variation of about 200% in the thermal resistances of the system in opposite directions is observed. This phenomenon is caused by the temperature dependence of the fluid adsorption at the fluid-solid interfaces. The fluid adsorption can increase the thermal resistance of fluid by reducing the number of non-adsorbed/free fluid molecules that controls heat transfer in the fluid, so the different levels of fluid adsorption in opposite directions of heat transfer can cause the thermal resistance of fluid direction dependent. The respective effect of fluid density, temperature gradient and fluid-solid interaction on the performance of this phenomenon is investigated. And it is found that the performance reaches the best at certain fluid density or certain fluid-solid interaction under given conditions.
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