Active micromixers - Micromixers Fundamentals Design and Fabrication - page 238

CHAPTER

7

Active micromixers

CHAPTER OUTLINE

7.1 Flow Instability in Microchannels.................................................................................................. 239
7.2 Pressure-driven Disturbance ......................................................................................................... 240
7.2.1 Actuation concepts for pressure generation ..................................................................240
7.2.2 Hydrodynamic instability ............................................................................................247
7.2.3 Pulsed source-sink chaotic advection..........................................................................249
7.2.4 Design examples........................................................................................................252
7.3 Electrohydrodynamic Disturbance.................................................................................................. 259
7.4 Dielectrophoretic Disturbance ....................................................................................................... 262
7.5 Electrokinetic Disturbance ............................................................................................................ 263
7.5.1 Instability caused by conductivity gradient...................................................................264
7.5.2 Instability caused by variation of electric field ..............................................................267
7.5.3 Instability caused by variation of zeta potentials...........................................................268
7.5.4 Design examples........................................................................................................270
7.6 Magnetohydrodynamic Disturbance ............................................................................................... 275
7.6.1 Straight channel configuration ....................................................................................275
7.6.2 Curved-channel configuration .....................................................................................276
7.6.3 Design examples........................................................................................................281
7.7 Acoustic Disturbance.................................................................................................................... 281
7.7.1 Vibration of a rectangular membrane ...........................................................................281
7.7.2 Vibration of a circular membrane ................................................................................285
7.7.3 Design examples........................................................................................................286
7.8 Thermal Disturbance .................................................................................................................... 291
References ......................................................................................................................................... 291

7.1 FLOW INSTABILITY IN MICROCHANNELS
Active micromixers are based on disturbance induced by external fields. Because flows in micro-
channels have Reynolds numbers far below the critical Reynolds number, transversal disturbance is
needed for making the interface between the two mixed phases to become unstable. A typical stability
analysis consists of the following seven steps [1] :

Formulating the governing equation and finding the basic solution to the physical effect. The
stability analysis applies to the basic solution x 0 of the problem. This solution can be a scalar or
a vector function.