Single-Channel Micromixers

Stratifiedflow a clear interface separates the two flows (lamination) and mixing occurs entirely by diffusion Vortex flow, the vortex creates secondary surface area Engulfmentflow the axial symmetry of the flow breaks up (see Section 4.2). 

The transition of regimes depends on Re and reactor geometry. In T-mixer, stratified flow is observed at low Re. Engulfment flow is observed at / e about 100. Engler et al. [11] proposed a parameter (K) to estimate the flow regime in T-mixers. 

The first transition from stratified to vortex flow was observed at about K = 15, whereas the transition to engulfment flow happened at /C = 40. The corresponding Re for two transitions in a 600 x 300 x 300 pm T-mixer are 45 and 150, respectively, which corresponds roughly to the observations presented in Section 4.2. 

Another way of increasing the mixing efficiency for Re in the range of a few hundred is the design of curved channels [28]. Here the mixing quality is improved by creating secondary flow pattern for Dean number (De) 140, where 

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Equation 4.17 enables one to estimate the mixing time. The choice of the characteristic dimension in more complex geometry is rather difficult because of multiple laminar vertices, which deform the layers along the three dimensions of space [17]. However, in the case of single-channel micromixers without any complex internal structures, the characteristic dimension can be assumed to be equal to its diameter (/ = df ). Mixing in T-mixers at low Re-numbers with stratified flow is discussed in Example 4.1 and 4.2. 

From the geometric point of view, the mixing in single-channel micromixers is not sufficient for fast reactions and, therefore, it needs to be improved further. In multilamination micromixers, the lamination improves mixing by reducing the striation thickness however, it requires additional mechanical power to create... 

FFMR, falling film microreactor PBMR, packed-bed microreactor MM, micromixer MBC, microbubble column MMR, microstructured mesh reactor SCR, single-channel reactor... 

Fig. 5. Single mixer and micromixer array in nickel on copper fabricated by LIGA technique and housing. Channel width 40 pm, Materials Nickel on copper, silver and titanium diboride. The silver and nickel-on-copper micromixers were realized by electroforming, the titanium diboride micromixer was fabricated by die sinking with LIGA electrodes...

In the case of Y- or T-shaped micromixers, a decrease in the channel width to shorten mixing time leads to a decrease of production volume per unit time. To solve this problem interdigital multilamination micromixers have been developed. In this type of micromixer, two fluids are separated into many small narrow streams, which are arranged to contact each other alternately. The mixing takes place at interfaces of such sub-streams by molecular diffusion. The IMM (Institute of Microtechnik Mainz) single... 

In interdigital multilamination micromixers, the small thickness of the lamellae leads to short diffusion paths, resulting in fast mixing. Further thinning of the liquid lamellae should lead to shorter diffusion paths and faster mixing. The IMM single mixer applied this concept by shrinking the channel width in the slit. A further extension of this concept leads to the... 

Another approach to single-phase synthesis is to separate the channels in the microfluidics from the site of particle formation. This can be achieved through the use of a microfiltration membrane system and dispersion microreactor and helps to minimize fouling of the fluidics. Double-loop micromixers in combination with air microchannels can also be applied to synthesis of metal nanoparticles with uniform diameters where the reaction time is significantly reduced. 

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