Numerical study of rapid micromixers for lab-on-a-chip applications

Effective mixing of liquids is essential in many applications such as drug delivery, DNA analysis/sequencing, pheromone synthesis in microbioreactors, and biological/chemical agent detections. Rapid mixing can reduce the analysis time and permit high throughput in lab-on-a-chip devices. The main objective of this dissertation is to numerically design a rapid mixer for micro/nanofluidic devices. Three types of micromixers with different driving mechanisms including pressure-driven, electrokinetic-driven and magnetic-particle-driven micromixers as well as a hybrid mixer based on both passive and active mixing mechanisms have been numerically investigated.; It is found in the pressure driven micromixer that the relay frequency is a critical factor affecting the micromixing.; For the electrokinetic micromixer, the effects of various design parameters such as channel width, relay frequency, external electric potential have been studied. The present study utilized two sets of time-dependent electric fields that are superimposed on a steady (pumping) electric field. The relay technique used in this dissertation not only stretches the fluid streams to increase the interfacial surface area, but also allows a self-sustained flow system for lab-on-a-chip devices.; In the hybrid micromixer, the asymmetric serpentine structure plays an active role in ultra-fast mixing within a short distance. With the designed hybrid micromixer, a very high mixing efficiency (95.6%) has been obtained within 1.0 second at x =500 mum for a 50 mum wide channel. Passive serpentine structures, however, induce flow impedance, and it reduces the flow velocity in the micromixer.; The difference with the pressure driven and electrokinetic micromixers is that neither one of them can obtain complete mixing in a straight channel; the magnetic-particle-driven micromixer with a simple actuation configuration studied in this dissertation is proved to be an effective mixer. The numerical simulations have shown that a magnetic micromixer consisting of a microchannel and a pair of electromagnets yields a very high mixing efficiency (>95%) within a short period of time (1 second). The effects of various design parameters such as applied magnetic actuation force and operating frequency have been studied in magnetic mixing. The numerical results of the magnetic-particle-actuated mixer demonstrate that a simple micromixer configuration is sufficient for a complete micromixing within a short distance and time period, with no need to fabricate complex serpentine channels. This simple mixing scheme not only provides an excellent mixing, even in a simple microchannel, but is also easily applied to "lab-on-a-chip" applications with a pair of external electromagnets.; In summary, the investigation in this dissertation reflects that both the hybrid electrokinetic mixer and magnetic mixer are very efficient and can be applied to meet the requirements of high throughput biosensor. It is believed that this research will provide guidance for the design of state-of-art of the micromixers for on-chip biosensor systems.