Single channel mixers

Figure 2.54 Single-channel silicon reactor with pre-mixer and outlet cooler [86]...

Besser et al. [86] studied the reaction in a silicon reactor fabricated by applying MEMS technology, namely photolithography and DRIE by inductively coupled plasma. Each reactor incorporated dual gas inlets, a pre-mixer, a single reaction channel and an outlet zone where the product flow was cooled (see Figure 2.54). The single channel was 500 pm wide, 470 pm deep and 45 mm long. 

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. 

In this barrier-embedded micro mixer, oblique grooves, placed at the channel s floor, and barrier structures at the channel ceiling replace the flights and barriers of the chaos screw [58], The placement of the structures, however, is not essential for the functions. The positions at the floor and ceilings may change without loss of performance two-sided structures are expected to exhibit improved mixing over single-sided structures. The barriers are placed periodically so that barrier-free zones intersect. 

Bednarova et al. [87] designed a single-plate PrOx reactor for a 1 W fuel cell based on MEMS technology, similar to [PrOx 1], The results of the simulation work described above were applied to optimize the reactor performance. The plate carried a pre-mixer and 29 channels each 12 mm long, 500 pm wide and 400 pm deep. Flow uniformity was verified by simulations. Full conversion of carbon monoxide was achieved at much lower temperature with [PrOx 1] and the selectivity towards carbon dioxide was 40%. 

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...

The process of wet-chemical etching of single-crystalline silicon was the first process suitable for the mass fabrication of micromechanical components [53]. Simple geometric structures like grooves, channels or membranes have been incorporated in microreactor components such as pumps, valves, static mixers and (most often) analytical devices. Bonding processes, either thermally or... 

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... 

Figure 7.19 shows the dependence of the mixing efficiency (rate) of the IMM single mixer on the flow rate. The increase of the flow rate causes a decrease in the absorption at 352 nm due to I2, which means an increase in the mixing rate. Above a flow rate of 100 ml/h, extremely efficient mixing can be achieved. The mixing efficiency also depends on the size of the channels in the distribution unit. When the flow rate exceeds 50 ml/h, the mixer with 25 tm channels exhibits better mixing ability than that with 40 )J,m channels. 

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