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Enlargement: New MEMS Capabilities

FLOW-3D MEMS simulation example
A 2D slice from a FLOW-3D simulation showing
the z-potential distribution and velocity vectors.

A new electro-osmosis model has been introduced in Version 8.2 of FLOW-3D. Electro-osmosis (EO) refers to the fluid flow that occurs when an electric field is applied to the electrical double layer (EDL), an intrinsic property of some fluid-solid interfaces causing a charge imbalance in the fluid adjacent to the interface. This phenomenon has proven to have great practical importance for micro-fluidic applications (MEMS and BioMEMS). Pressure-driven flows in small channels exhibit an average velocity proportional to the second power of the transverse dimension of the channel, thereby requiring large pressures to pump fluids in small channels. EO, however, produces flows that are roughly independent of channel size.

In addition, due to the absence of moving components, microfluidic control and fluid handling devices using EO are more reliable and easier to maintain compared with microsystems that have moving surfaces such as valves or pistons.As a result, EO is increasingly being adopted in micro-devices to provide fluid motions typically associated with pumps, valves, mixers, etc. Enlarging FLOW-3D to have an EO capability will greatly enhance its use for optimizing MEMS and BioMEMS devices.

The EO model added to FLOW-3D uses a robust GMRES-based solver that combines pressure and EO-driven flows with or without free surfaces and in one or two-fluid systems. The accompanying images demonstrate the application of the EO model in two sample cases: a micro-pump and micro-mixing. These and many other practical applications are now part of the enlarged scope of FLOW-3D.

micro-pump and micro-mixer geometry
Pump geometry is shown

Micro-pump

By creating a series of deep slots in a microchannel, and then applying a potential across the channel, fluid flow can be controlled.

Micro-mixer

By creating a non-uniform z-potential on the channel walls, a helical flow inside the channel is induced. The picture above shows the problem geometry with strips indicating places where the z-potential is imposed. The image on the left, from a FLOW-3D simulation, shows the fluid stretching and folding (mixing) as indicated by marker particles.