Recombination micromixers

Schonfeld, F., Hessel, V., Hofmann, C., An optimised split-and-recombine micromixer with uniform chaotic mixing. Labchip 2004, 4, 65-69. 

Manifold split-and-recombination micromixers are also popular and powerful micromixers. " In this type of micromixer, two solutions to be mixed are introduced into a channel and combined. Then, the mixture is split into two streams in such a way that each stream contains segments of two different solutions. The two streams are then introduced into the next channel and recombined so that the number of solution segments increases, as shown in Figure 7.10. 

The Toray Hi-mixer is a special type of manifold split-and-recombination micromixer. The structure of the Hi-mixer is shown Figure 7.12. In the Hi-mixer, when two layers of the solutions enter the mixing element, they are split into eight layers by using twist walls in the element. Therefore, in this method, the number of layers increases exponentially by repeating the operation (4" after the wth iteration). 

The Yamatake YM-1 micromixer is another type of split-and-recombination micromixer (Figure 7.13). As shown in Figure 7.13, the two solutions to be mixed are distributed into many streams in the first part of the mixer. Then, several split-and-recombination operations are performed sequentially to increase the number of segments, leading to fast mixing because of the short diffusion path. 

SAR Split-and-recombine micromixers, sequential lamination micromixers... 

Lee S, Kim D, Lee S, Kwon T (2006) A split and recombination micromixer fabricated in a PDMS three-dimensional structure. J Micromech Microeng 16 1067. http //dx.doi.org/... 

Concerning mixing of highly viscous media, it may worth mentioning the type of split-and-recombine micromixers exemplified on the so-called Caterpillar Micro... 

Figure 22.3 Functional principle of the split-and-recombine micromixer CPMM-V2 (IMM). (a) Representation of one mixing step the colors blue and red represent two liquids entering the mixing step the complete mixer is made up by a sequence of such mixing steps, (b) Simulated flow pattern at different cross-section points overthe length ofthe first mixing step. Source Institutfur Mikrotechnik Mainz GmbH.

Figure 22.9 Comparison of emulsions formed in YM-1 split-and-recombine micromixers of the same design but using different mixer materials (a) ac lic resin mixer (b) aluminum mixer [18].

Figure 22.13 Micromixers employed in the experimental setups for surfactant dispersion. The V-type mixer of FZK (a) is a parallel multilamination micromixer whereas the caterpillar mixer of IMM (b) is a split-and-recombine micromixer (serial multilamination) [3].

P. Lob, et al., Split-and-recombine micromixers for high and low Reynolds number applications. Presented at the NAMF Mixing XX Conference, Parksville, Vancouver Island, Canada, 25 Jime-1 July, 2005. 

Split-recombine micromixers with repeated physical separation of fluid streams by branching into separate channels and recombination of channels and streams... 

Figure 4 Micromixers, (a) Interdigital structure of a multilamination micromixer. (b) Principle of split-and-recombine static micromixers. (Source IMM.)...

When a T-shaped mixer is used, the product selectivity is essentially the same as for the macrobatch reactor (Scheme 6.4). The use of the YM-1 mixer, a splitting-and-recombination-type micromixer (see Chapter 7), increases the selectivity, however, a significant amount of dialkylation product is still produced. The use of the IMM multilamination-type micromixer results in excellent selectivity of the monoalkylation product. The amount of dialkylation product is very small. Therefore, the product selectivity strongly depends on the manner of mixing. 

When two solutions enter the micromixer, the number of segments is doubled in one split-and-recombination operation. Therefore, in this method, the number of solution segments is increased exponentially by repeating the operation sequentially along the channel (Figure 7.11). After the nth split-and-recombination iteration, the number of segments increases to This operation decreases the diffusion path significantly... 

While the multi-lamination micromixers use a parallel approach, the split and recombination units use a linear approach by splitting the flow, recombining it and by rearranging it, almost always with some recirculation flow [60, 63, 65, 66, 84,85]. Designs used to achieve this flow include, but are not limited to, fork-like, ramp-like, cross-like, and curved. Mae et al. reported a two-phase mixer designed to create a water-oil emulsion that could process up to 5 L h (YM-1) and 20 L h (YM-2) [63]. Figure 7.6 shows the YM-1 structure. 

Similar to parallel lamination micromixers, sequential lamination micromixers [also called split-and-recombine (SAR) micromixers] rely on an exponential increase in the contact surface area and decrease in the length path to achieve a shorter mixing time. The difference between the two types of micromixers is the method used to achieve lamination of the fluid to be mixed. As suggested by the name, the lamination in sequential lamination micromixers is obtained by sequential processes of splitting and rejoining the fluids (Fig. 4a) [84, 86-89]. 

Different geometries for SAR micromixers have been proposed, such as ramplike [86] and curved-like [90] architectures. However, in order to achieve exponential sequential lamination, three steps are typically required flow splitting, flow recombination, and flow rearrangement (Fig. 4a). 

Chen et al. [114] reported a more complex structure derived from the connection of two hehcal flow channels with opposite chirality, and called it a topological mixer. By splitting, rotating and recombining the flow streams, the micromixer provided an effective and fast mixing at low Re between 0.1 and 2. 

Mae K, Maki T, Hasegawa I, Eto U, Mizutani Y, Honda N (2004) Development of a new micromixer based on split/recombination for mass production and its application to soap free emulsifier. Chem Eng J 101(l-3) 31-38... 

Figure 8a illustrates typical fluorescent images of a micromixer, indicating the mixing behavior at increasing distance downstream at Re = 0.1. The obstruction micromixer is a planar passive microfluidic mixer with diamond-shaped obstructions within the mixing channel to break up and recombine (i.e., laminate)... 

One of the promising designs is the modified Tesla structures [46]. It uses the Coanda effect to split part of the fluid stream and direct it so that it recombines with the opposing flow of the other part of the stream. Coanda effect micromixer relies on the redirection of a flow by a special guiding structure that creates new interfaces within the flow [47]. This special passive structure provides good mixing at low flow rates. In this way the Coanda mixer can also be seen as a special realization of the SAR approach using recycle flows [32]. 

An example for microchannels with structured internals are caterpillar micromixer, where the surfaces consist of ramp-Hke structures, moving the fluid constantly up and down and the fluid contact is achieved by a sequence of repeated sphtting-reshaping-recombination processes [5]. Sometimes simple foam stacks are used as static mixer for dispersing two immiscible phases. 

Interdigital mixers and micromixer with the split-recombine technique Single microchannel operating in annular flow regime Microstructured falling film reactor Mesh microreactor... 

Numerous micromixers have been designed based on the prindple of laminar static mixers, where the fluid undergoes a periodic process of splitting, rotation and recombining. These mixers are inspired by chaotic mixing, where the geometry of the system imposes spatial periodicity. 

Mae et al. proposed a micromixer based on repeated splitting and recombination and demonstrated its application for extraction using an emulsion (abbreviated as YM-1) [30]. A soap-free emulsion with a diameter of the order of 1pm can be produced in a short contact time of 0.1 s. The maximum production capacity of a single mixer is 200tyr , which is sufficient for the industrial production of fine chemicals and pharmaceutical compounds. Figure 12.8 shows the results for the extraction of phenol from dodecane into water using the YM-1 and an IMM mixer. 

Sprogies et al. compared micromixers for use in extractions based on emulsions [32]. They revealed that a multilamination mixer is more efficient than a simple T-junction, whereas a nozzle-type mixer and a split-and-recombine mixer show the best results for emulsification and thus for extraction. 

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