The Electroosmotic Flow Of Non-Newtonian Fluids In A Microchannel

With the development of biochip and chip experimental technique, the control techniques of microfluidic become focus of the research. Microfluidic flows are readily manipulated using many kinds of drive mechanism, such as surface tension, pressure gradient, electric field, magnetic field, Centrifugal rotating forces and so on. Microfluidic systems usually use an external electric field to drive and control the fluid flow within the microchannel. The flow induced by external electric field is called electroosmotic flow (EOF). Nowadays, the electroosmotic flow is widely used in biology, chemical engineerig and medicine fields due to its high efificiency, ease of control, convenient integration and no destroy to mechanical part.Many theoretical, experimental and numerical investigations of fully developed and unsteady EOF through microchannels with different geometrical shapes have been studied since the EOF phyenomenon was first put forward in1809. Many good research results were obtained. However, most of the fluids used in their studies were limited to Newtonian model. In fact, the microfluidic system is mainly used in biochemical analysis, medical treatment and drug manufacture fields. The fluids in these fields are normally decribed by non-Newtonian model. Based upon the above consideration, this paper will study the EOF of non-Newtonian fluids through microchannels with different geometrical shapes. The constitutive relations of the non-Newtonian fluids are depicted by general Maxwell model and Jeffreys model. Firstly, we studied the periodic EOF of non-Newtonian fluid produced by AC electric field in different microchannels. By Laplace transform, we then investigated the unsteady EOF of non-Newtonian fluid in different microchannels.Moreover, due to the unavoidable interaction between macro-molecules in non-Nowtonian fluid and the channel surface, polymer depletion and adsorption phenomena will be produced. This paper took the depletion effect into account, and studied the EOF of non-Newtonian fluids by suing immiscible two-layer model. In this case, the depletion layer near the wall is regarded as Newtonian fluid, while the bulk fluid except depletion layer is taken as non-Newtonian fluid.The linearization to Poisson-Boltzmann equation electrical potential satisfied is often used. This is valid to small surface Zeta potential. However, for the higher surface Zeta potential, for example, larger than25mV, the linearized Poisson-Boltzmann equation is invalid for most engineering application. Thus this thesis studies the high Zeta pontial situation in some cases by keeping the non-linear term in Poisson-Boltzmann equation.The idea to obtain analytical solution of EOF of non-Newtonian fluids in a microchannel is giving the distribution of electrical potential from Poisson-Boltzmann equation firstly. Then the charge density distribution can be obtained. Finally the Navier-Stokes equation will be modified by substituting the electric force and constitutive relation of non-Newtonian fluid into the Navier-Stokes equation. Under appropriate initial and boundary conditions, the EOF velocity in different microchannels can be obtained by using several mathematical physical methods, such as separation of variables, Laplace transform, Green functions, etc.By theoretical analysis and numerical computations, the influences of electric oscillating Reynolds number Re, electrical width K, relaxation time λ1, retardation time λ2, permittivity constant ratio ε, density ratio p, viscous coefficient ratio y and wall Zeta potential ψo on velocity amplitude are presented. These analytical solutions provide the theoretical guidance for the reasonable design of microfluidics.