Co-laminar streaming

In conventional single phase microfluidic systems, flow in the microchaimel is laminar a parabolic velocity profile is established with fluid velocity zero at the channel walls and maximum at the channel center [18, 21] (Fig. 9a). There are two implications to this behavior (1) a reagent sample plug will constantly dissipate along the microchannel, and (2) the mixing of samples could be very slow in co-flow streams. 

Figure 18.17 Top left schematic representation of the microsystem used for the production of biodegradable microgels. Top right insufficient shear between the aqueous dex-HEMA and mineral oil phases resulted in co-flowing laminar streams. Bottom the addition of surfactant in the continuous oil phase facilitated regular droplet break-off From Ref [20].

Figure 7.20B2 depicts a typical flow pattern. On each side, two fluids of different refractive indices merge to form co-injected laminar flows and establish a CaCl2 concentration distribution. The convergence of co-injected streams from both sides eventually leads to a complete hyperbolic secantlike refractive index distribution in the main channel. The refractive index profile within the main channel can be adjusted readily by changing the flow rates from different inlets [20]. 

A similar approach to reduce diffusive nuxing is the use of a porous separator between the co-laminar fuel and oxidant streams, which can facilitate reduced crossover and mixing or enlarged electrochemical chamber dimensions beyond... 

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