Intersecting channel mixing

At a certain point they merge and mixing takes place by diffusion at constantly recreated and renewed interfaces, (b) A similar flow arrangement with square bed objects however, this time a micromachined packed bed is shown, (c) Artificial new structure of a packed bed where some objects of the packed bed have been removed. Now, flow conduits exist which are intended to promote lateral mixing, (d) Bimodal intersecting channel micro mixer, which is a micromachined design resembling the idea depicted in (C) [160] (by courtesy of ACS). 

Figure 1.176 A suggestion as to how the flow might develop in the bimodal intersecting channel micro mixer. Distinct zones with small and large channels serve to promote mixing by diffusive and convective transport, respectively [160] (by courtesy of ACS).

M 85] [P 75] In order to determine reaction kinetics by a stopped-flow method, the mixing step within a microfluidic system was improved [161]. Traditionally, an efficient external T-channel mixer is used for this purpose. Now, the bimodal intersecting channel micro mixer was integrated into the system. The mixer has the following advantages over the current state of the art ... 

Figure 1.178 Stopped-flow enzymatic assays when using an external T-channel micro mixer, the bimodal intersecting channel micro mixer and the flow before the micro mixer with only diffusion mixing [161 ]...

It could be shown that the bimodal intersecting channel micro mixer clearly improves the mixing performance. The corresponding axial concentration profile is virtually flat, i.e. mixing has led to the same concentration within the channel [161]. Without the use of the micro mixer more or less the initial concentration profile is found, i.e. a two-sectioned profile with two constant concentration values due to the bi-laminated structure. 

Almost at the same time, Ermakov et al. [3] presented a numerical model for electrokinetic transport in a simple cross-linked microchannel and a T-intersection microchannel. This model considered two sample species and was numerically solved using the finite difference method, where an intermediate velocity was introduced to generate an equation for the pressure and the continuity equation was used as a condition to ensure the mass conservation is satisfied. Sample focusing in the cross microchannel and sample mixing in the T-intersection channel were studied, and the effects of the electroosmotic mobility, electrophoretic mobihty, and apphed... 

When tripropylamine or tributylamine is used, mixed ZSM-5/ZSM-11 phases are formed. Their nature seems to be determined more by the zeolitic channel filling than by the location of the organic molecules at the channel intersections. 

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. 

The mixing results of the bimodal intersecting mixer show that microstructured analogs of packed-bed structures can mix efficiently. Small micro channels resemble... 

The two symmetrical side channels are arranged like a Y-configuration, which attaches at its ends two times each the main channels [164], At these intersections, mixing takes place via diffusion. 

M 90] [P 82] As a symmetrical flow mode, an operation is described in which the fluorescent dye and buffer solutions are guided in the two main channels side-by-side [164], Buffer solution is introduced from the two side channels and can mix with the main channel at the two intersections. 

The characteristics of electrokinetically controlled fluid flow in microchannel manifolds has been studied in a systematic way by Harrison and coworkers [28, 30]. An illustrative demonstration of the potential of this approach is shown in Fig. 2 for the controlled dilution of a fluorescein solution under voltage control. In parallel with a stepwise decrease of the potential applied to the fluorescein reservoir, a decrease of fluorescence signal downstream after the junction is visible in Fig. 2. As long as the ionic strength and pH in each supply channel is the same (same jieo), mass balance is automatically fulfilled, and the incoming flows at the intersection will be exactly balanced by the outgoing flow of the mixed components (otherwise, mass balance would be enforced by additional hydrodynamic or secondary internal flows). This way of mixing fluids was also... 

The first experimental demonstration of such a device has been published by Jacobson et al. [53]. Amino acids were injected by a gated injection scheme, separated in a 7 mm channel and subsequently labeled by controlled mixing with an o-phthaldialdehyde reagent solution at a T-intersection. The separation efficiency achieved, however, was relatively poor and the inadequate kinetics of the labeling reaction caused significant band broadening. 

A micromixer (100 pL) was constructed on a quartz chip with multiple small channels (5 pm wide) intersecting 45° with the main channels (27 pm wide) (see Figure 3.39). EOF flow of two solutions containing different concentrations of fluorescein was initiated to achieve mixing based on the principle of eddy diffusion after splitting in the smaller channels [493]. 

In the appendix the solution of the equations for flow and matrix diffusion in a channel with variable properties is derived. The solution shows that one can follow a constant stream q through a path with arbitrarily varying velocities, widths and material properties. When one attempts to follow a packet of water through the network the packet, however small, will have to divide at fracture intersections. If it is a well-mixed stream it will divide into the outgoing streams in proportion to the total flowrates in the outgoing streams. 

Equation (1) is convenient to use in cases where the tracer mass input varies over time. It can then be convoluted with the input mass flow that may vary in time. The effluent from a channel is mixed with the effluents from the other channels meeting at a channel intersection. Tlie fluid is then redistributed to the channels leaving the intersection. 

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