微尺度旋轉流動及熱傳之理論研究

• Main Author: 王勝弘
• Other Authors: 宋齊有
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/24681106301439522712

博士 === 國防大學中正理工學院 === 國防科學研究所 === 91 === The microscale rotating thermal-fluid flow characteristics are explored by theoretical model and numerical simulation in this dissertation. The research methods include electrokinetic flow model and molecular dynamics simulation. In practical applications, the rotor and stator parts of a micro motor or micro bearing have relative motion to the others and may be made of dissimilar materials and thus possesses different zeta potentials on wall surfaces. Therefore, before studying the electrokinetic effects in the microscale rotating flow, the present study first considers a Poiseuille and Couette liquid flow in a microchannel of two uniformly charged parallel plates at different electrostatic, motion and thermal boundary conditions. The Navier-Stokes equations with consideration of electric body force stemming from streaming potential are employed in momentum balance. The linearlized Poisson-Boltzmann equation for the electrical potential solution is adopted and solved analytically. Then, the effects of asymmetric boundary conditions including relative wall motion, unequal zeta potential and unequal thermal condition on two walls on the electrokinetic flow can be explored. And, the results can be applied to the studies of more complicate rotating electrokinetic flow. In the study of rotation-driven electrokinetic flow in microscale gap region of rotating disk systems, a novel theoretical model in self-similar form for rotating electrokinetic flows is developed and solved by a shooting method based on a standard Runge-Kutta scheme. The only considered flow configuration is a rotor-stator disk system. The concentration distributions of ions are obtained from Nernst—Planck equations for convection-diffusion of the ions in the flow field. The fluid viscosity and permittivity are not assumed as constant but the function of the local fluid temperature. The major characteristics in the study include: (a) to develope a novel theoretical model in self-similar form for rotating electrokinetic flows without assumptions of equilibrium state of ion distribution, low-degrees of EDL overlap or low potential, isothermal flow, and constant properties. (b) the unique flow patterns are explained by the electro-hydrodynamic mechanisms, and (c) by using the present theory to demonstrate influences of various approximations with neglected ion convection, low electric potential and/or constant fluid properties on the electric force and flow solutions. In the molecular scale rotating flow, non-equilibrium molecular dynamics simulation is performed to model fluids behaviors confined in an enclosed cylindrical container with a rotating lid disk. The major concerns of the study are fluid density distribution, velocity slip and the validity of the conventional principle of dynamic similarity in this molecular-scale rotating fluid flow. The walls of the rotating cylindrical containar are constructed by the molecules. Two intermolecular interactions potentials, shifted and truncated Lennard-Jones potential and Weeks-Chandker-Anderson potential, are considered for comparison. In addition, simulations based on the boundary conditions with and without wall barrier layers are compared.