ELECTROKINETIC FLOW OF NON-NEWTONIAN FLUIDS THROUGH RECTANGULAR MICROCHANNEL

Abstract

A basic understanding of the fluid flow characteristics in an electrically charged micro-channel is very important in the field of research for micro and nano-fluidcs. Micro-channels have a lots of industrial uses starting from p1-I and temperatures instruments to fluid actuators (micro-nozzles, micro valves,microrheometers) and in the design operation of micro-fluidic equipments like Micro-Electro- Mechanical systems (MEMS) connected instruments ,diagnostic micro-devices,biomedical microchips.The significant reduced quantity of the sample consumption and improved rate of heat/mass transfer and chemical reactions, is the major advantage of the micro fluidic devices (Ren. And Li ,2004). Laminar flow is the definitive characteristics of the microfluidics.The requirement for such devices application is the capability to carriage, improve and progression of fluids by micro-channels,So the meaning of the characteristics of micro-channel flow (such as distribution of pressure, flow resistance, and flow profiles) is very important parameter for optimal design of MEMS associated flow equipment. The behavior of fluid flow in an electrically charged channel is affected by the electro kinetic results.Usually,a solid surface endures electrical effects.Once the solids surface is taken in to interaction with the electrolyte, the counter ions of the solution gets engrossed towards the charged barrier and colons are repelled from the wall.By rearranging and balancing of the charges there is the creation of an area called as electrical double layer (EDL).Electrical double layer results due to the deviation in electric potential which is far from the surface.(Bharti et.al ,2010) The net charges passed to the down streamside, when a liquid is enforced through a channel in presence of an applied hydro static pressure, in the electrical double layer which results an electric current in the pressure-driven flow direction.This current is known as the streaming current. Similar to this flowing current, an electro static potential exist there which is known as streaming potential (Chun,2002).lt is a potential difference that formed with the micro-channel.The net charges in electrical double layer are driven to transfer in a direction that is reverse to the flowing current or reverse to the pressure-driven flow. This flow of ions in the reverse way of the flow which is driven by pressure, will produce transmission current. Obviously, ions moving in the liquid will jerk the liquid to transfer with them.Due to the presence of the induced streaming potential ,the motion of net charges will generates a flow of liquid in reverse to the wayof flow which is pressure-driven. Generally, in the direction of pressure reduction, the flow rate will be reduced. If the decreased flow rate is equated with the flow rate that is determined by basic fluid mechanics,without taking the existence of EDL, it is found that fluid will have the greater viscosity. This effect is known as electro-viscous effect. In microfluidic applications, complex fluids are often manipulated.These fluids shows non-Newtonian now behavior like shear related viscosity and visco-elasticity (Bharti et. Al 2009). Normal modeling of electrokinetic flow of Newtonian liquid is not valid, a common rheological model for shear dependent viscosity fluid is the power law model. For describing the fluid behavior for this case. The rheology of fluid is, for simplification expected to be defined by the non-Newtonian power law viscosity model.According to this model viscous stress tensor is defined as the product of degree of strain tensor to the viscosity.This model does not asymptote for Newtonian behavior in the limits of both zero and enormous shear rates,it is advantageous in application an dease to explain its use in determinations of shear related flow behaviors. This work is concerned with the shear flow of non-Newtonian fluids in an electrically charged channel. Inspite of fundamental and pragmatic significance, very little is known about the rheological effects on shear flow through electrically charged micro-channels. Therefore the object of this work is to fulfill the vacant place in the available works.