Curved channel mixing

The Poincare map method was applied by linxiang et al. [140] to study mixing in curved channels. 

The generation of secondary helical flows in suitably curved channels, known as Dean vortices, is not an entirely new fluidic phenomenon discovered at the micro scale actually it was found already also for wound tubings of conventional diameter (see a summary in [152]). In-depth studies concerning Dean vortices in curved channels were made in the framework of various applications such as filtration, heat exchange, friction and mixing. 

The relative transverse velocity of the curved channel corresponds well with data published for bas-relief structured channels [152], Hence, also the very simple design of a curved channel can lead to efficient mixing. 

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... 

Dean flow as a static mixer The use of the fluid inertia across a curved channel can create turbulence. The flow of fluids in the meandering channels undergoes mixing due to the inertia of the fluid in the flow direction. An example is shown in Figure II.6, while the Dean number is defined in the side bar. 

A continuous lipidic cubic phase is obtained by mixing a long-chain lipid such as monoolein with a small amount of water. The result is a highly viscous state where the lipids are packed in curved continuous bilayers extending in three dimensions and which are interpenetrated by communicating aqueous channels. Crystallization of incorporated proteins starts inside the lipid phase and growth is achieved by lateral diffusion of the protein molecules to the nucleation sites. This system has recently been used to obtain three-dimensional crystals 20 x 20 x 8 pm in size of the membrane protein bacteriorhodopsin, which diffracted to 2 A resolution using a microfocus beam at the European Synchrotron Radiation Facility. 

The actual device consists of two parallel rows of five mixing elements each [125, 126], The lateral displacement and recombination of the sub-channels are done via 90° angles. In contrast, the variation of channel depth and width is done in a continuous fashion, yielding a curved horizontal and vertical structure. In particular, the curved floor structure is demanding, since a real 3-D and not just a multi-level microfabrication process is needed. 

One stream is split into two curved sub-streams which simply merge and then instantly split again [143], The mixing is performed by several crosses in a row which are connected, with two channels for inlet and two for outlet. This process is repeated many rimes. Typical dimensions are not given and the fabrication is also not specified. Since no testing is reported, which is not surprising for an industrial proprietary method, no further information on this mixer is given below. 

Mixing by Helical Flows in Curved and Meander Micro Channels Most Relevant Citations... 

The first design has a slightly curved serpentine channel comprising square columns. The second design is an arrow-shaped channel [159], Circular holes, two before and one after the mixing channel, serve as fluid reservoirs for both designs. 

Jiang, F., Drese, K. S., Hardt, S., Kupper, M., Schonfeld, F., Helical flows and chaotic mixing in curved micro channels, AIChEJ. 2004, 50 (9), 2297-2305. 

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