Micropumping mixing

Figure 1.46 Valveless micropumping mixer with two mixing chambers.

T. Korenaga, X.-J. Zhou, T. Moriwake, H. Muraki, T. Naito, S. Sanuki, Computer-controlled micropump suitable for precise microliter delivery and complete in-line mixing, Anal. Chem. 66 (1994) 73. 

One of the simple ways to achieve active mixing is to induce a pressure field disturbance. Active micromixers relying on this strategy have been reported from different authors [43, 156-159], Deshmuck et al. [156, 157] proposed a T-junction microfluidic chip with an integrated micropump that alternatively drives and stops the flow within the microdevice to create a segmented flow. 

The mechanism of action of the controlled-release micropump is unclear. With a pressure difference, the rapid oscillatory movement of the piston during augmented delivery may be responsible for the increased delivery rate by lowering the overall resistance of the micropump to bulk flow (35). When only a concentration difference exists, on the other hand, augmentation can be attributed to a pressure difference superimposed during piston movement on the basal concentration difference, or to a mixing effect associated with piston movement. The physical relationship between piston movement and augmentation remains to be defined. 

One of the passive mixers was developed using capillary forces to insert and hold the liquids in separate chambers, which are connected via a small gap [45]. It is a self-filling micromixer device and does not require micropumps referring it as an automixing device. This device was developed on a chip with two channels with variable volumes that are separated by a thick porous plate through which mixing takes place by diffusion. The idea was to use the capillary forces to fill one capillary with two liquids. 

Active techniques improve pumping and mixing using mobile parts or external mechanical, electrical, magnetic, or aconstic forces. Active structures are based on MEMS devices, and allow the creation of actuation systems for the transport of fln-ids in microchannels. Micropumps and microvalves are examples of these structures (Rife et al., 2000 Bradley et al 1995), that can achieve proper flow rates, with values that can achieve 1 mm/s in 1.6 x 1.6 mm channels, as determined by Rife et al. (2000), or 1.15mm/s in Ixlmm channels, as obtained by Bradley etal. (1995). 

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