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Modeling Electrokinetic Phenomena

Figure 1
Figure 1: Channel Geometry


Figure 2
Figure 2: Pathlines in channel


Figure 3
Figure 3: Velocity vectors at
different cross sections

The term "electrokinetic phenomena" usually refers to electrophoresis and electroosmosis,which are phenomena generated when an electrolyte fluid interacts with solid surfaces causing a charged layer to form at the interface between the solid and the liquid. Application of an electric field acts on the charges to generate relative motion between the solid and liquid materials.

Both processes are driven by an external electric field and have significant importance in microtechnology. In particular, electroosmosis is employed extensively in BioMEMS ("lab-on-a-chip") technology as a transporting mode to control liquids through pumping, valving, mixing, splitting, etc. Electroosmosis is also used to deliver solute samples interface between the solid and the liquid. Application of an electric field acts on the charges to generate relative motion between the solid and liquid materials. of nanovolumes in microfluidics used for chemical and biological analysis and medical diagnoses.

A robust model to simulate electroosmosis was introduced with FLOW-3D Version 8.2. With this model, users can investigate combined pressure and electroosmosis-driven flows with or without a free surface, electroosmosis induced by non-uniform zeta-potential, and electroosmosis in one- or two-fluid configurations.

An example of the use of electroosmosis to mix two fluids, and of the ability of FLOW-3D to model this process, is highlighted here. Figure 1 shows a micro-mixing device and its dimensions. On its floor are patterned charge strips. The device has two inlets and one outlet. The electroosmotic flow and mixing of two fluids entering are to be simulated.

Figure 2 shows particle pathlines in the microchannel. Figure 3 displays the velocity vectors in different channel cross sections. The color in Figure 3 indicates the distribution of one fluid fraction in a two fluid mixture.

Modeling electroosmotic flow and mixing in tiny devices such as this micromixer is quick and easy using FLOW-3D's new electroosmosis model. The results are easy to see…not so in the real world, where seeing micron-level fluid activity can be a real challenge.