Mixing passive mixers

Chung Y, Hsu Y, Jen C, Lu M, Lin Y (2004) Design of passive mixers utilizing microfluidic self-circulation in the mixing chamber. Lab Chip 4(l) 70-77... 

Passive mixers can be categorized according to the arrangement of the mixed phases, i.e., parallel... 

Microfluidic-based mixers allow ultrafast reactions to take place in the kinetically limited regime by achieving faster mixing, which is usually obtained by a complex coupling of increases in the advective flux and interfacial area. The micromixers that have been developed can be categorized into active and passive mixers. 

As mentioned above, radial mixing is crucial to get narrow RTD. Therefore, the use of passive mixer helps equalizing the radial concentration in the laminar flow domain. It is known that static mixer allows to obtain narrow RTD in tubular reactors even with high viscous media [18]. The beneflcial effect of radial mixing can also be expected in microstructured mixers. Boskovic et al. [19,... 

The simplest passive mixers are often used for characterizing mixing under well-defined conditions (typical geometries are shown in Figure 4.15). If a T-mixer is considered, three flow regimes are observed (Section 4.2) ... 

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. 

In contrast to the presented passive mixers, active micromixers rely on external power input to introduce perturbations within the laminar flow to accelerate mixing. A selection of different external perturbation sources are summarized in Table 4.1 and are discussed briefed here. 

Passive mixers No energy is input other than that used to mobilize the fluid within the device. The passive mixers that have been developed use serial or parallel lamination, injection, chaotic advection, or droplet formation. The most popular approaches to the mixing step for biochemical and chemical reactions involve increasing the contact area between two reagent streams. This... 

M 20] [P 19] An investigation of the flow patterns in the mixer outlet was made by dilution-type dye imaging [30], On contacting the two streams only in the mixer devices without any membrane actuation (static or passive case), a bi-layered system results with no obvious degree of mixing, as is to be expected. 

The use of the Coanda effect is based on the desire to have a second passive momentum to speed up mixing in addition to diffusion [55, 163], The second momentum is based on so-called transverse dispersion produced by passive structures, which is in analogy with the Taylor convective radial dispersion ( Taylor dispersion ) (see Figure 1.180 and [163] for further details). It was further desired to have a flat ( in-plane ) structure and not a 3-D structure, since only the first type can be easily integrated into a pTAS system, typically also being flat A further design criterion was to have a micro mixer with improved dispersion and velocity profiles. 

Hessel, V., Lowe, H., Micro mixers-a review on passive and active mixing priciples, Chem. Eng. Sci. 2005, in print. 

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