Parallel Channel Devices

Gaiser and Kottke [S] have used a method similar to that developed by Marcinkowski and Zielinski [6] to visualize heat transfer and mass transfer improvements achieved by OCFS in comparison to parallel-channel devices. Their physicochemical method is based on convective mass transfer and produces colorization of the body wall as gas is passed through the support structures and reacting molecules are transferred from the gas bulk to the prepared wall material. The intensity of the colorization is a visual representation of the amount reacted and, since the surface reaction is very fast, of the mass transfer. Figure 7 shows the result of a typical such experiment. 

Experiments show that with CX FS, mass (or heat) transfer from the bulk gas to the catalyst surface can be improved by factors of 5 to 10 compared to parallel-channel devices. For catalytic reaction processes in which the rate of reaction is not the limiting step, every such improvement of mass transfer leads to a higher overall reaction rate. 

However, many reactions of commercial interest have chemistry, mechanical, or system requirements that preclude the use of cross-flow reactors. Processes cannot use a cross-flow orientation primarily because of high temperatures and the need to internally recuperate heat such as steam methane reforming (SMR) [12, 13] and oxidation reactions [14]. Counter- and coflow devices require a micromanifold to dehver sufficiently uniform flow to each of the many parallel channels. 

This device is based on multiple parallel bi-lamination using bifurcation cascade for generating multiple thin fluid olamellae [25]. The first feed stream is split into multiple sub-streams via a bifurcation cascade in a similar way this is done for the second feed stream in another level. The corresponding sub-streams enter via nozzles into the first level. Here, the end of the channels of the bifurcation cascade and the nozzles lie next to each other. Thereby, bi-laminated sub-streams are formed and enter many parallel channels of an inverse-bifurcation cascade. These are recombined to multilayered stream in one main channel which has a serpentine shape, i.e. comprises extended length. 

For another investigation, amide formation was used as a model reaction to demonstrate the performance of parallel processing in micro-channel devices [23]. The target of such processing is combinatorial synthesis, the provision of multiple substances within one run. 

As micro devices, mixers from various suppliers (]R 19], [R 17]) were used [37]. These devices were each connected to a PTFE tube of length up to 150 cm. In addition, a tailor-made micro reaction system with parallel channels and integrated cooling was used (]R 26]). 

The liquid enters the micro channel device via a large bore that is connected to a micro channel plate via a slit (Figure 5.2). The slit acts as a flow restrictor and serves for equipartition of the many parallel streams [1, 3, 4]. The liquid streams are re-collected via another slit at the end of the micro structured plate and leave the device by a bore. The gas enters a large gas chamber, positioned above the micro channel section, via a bore and a diffuser and leaves via the same type of conduit. 

P 30] A 120 parallel micro-channel device was employed (see [R 2] for a description of the corresponding single-channel device) [7]. The total flow rate was 1-10 ml h The contact length was 14 mm the channel cross-section was 3000 gm. A residence time of 2-20 s resulted. 

The selection of a mobile diase for the separation of simple aixtures may not be a particuleurly difficult problem and can be arrived at quite quickly by trial and error. Solvent systems can be screened in parallel using either several development chambers or a device like the Camag Vario KS chamber, which allows the simultaneous evaluation of a number of solvents by allowing each of these to migrate along parallel channels scored on a single TLC plate [8]. However, whenever the number of components in a mixture exceeds all but a small fraction of the spot capacity for the TLC system, a more systematic method of solvent optimization is required. 

The output parallel channels of the multichannel device are positioned at different distances dy from each other in such a way that channels of each pair are separated by a unique distance, as shown in Fig. 10.5. In other words, di2 / d23 / / dy. In this way all spatial frequencies k,r each of them corresponding to the... 

The process is designed as a dynamic layer crystallization. The heart of the experimental equipment is an autoclave which is mounted in a way that its incline can be adjusted between 0 and 90 degrees (see Figure 6). An important feature are four 35 mm diameter windows, which allow to observe the beginning and the end of the trickling film on the crystallization device (see Figure 7). It was necessary to divide the crystallization surface into six parallel channels,... 

The distribution of gas over all parallel channels in the monolith is not necessarily uniform [2,5,6]. It may be caused by a nonuniform inlet velocity over the cross-sectional area of the monolith, due to bows in the inlet tube or due to gradual or sudden changes of the tube diameter. Such effects become important, because the pressure loss over the monolith itself is small. Also, a nonuniformity of channel diameters could be a cause at the operative low Reynolds numbers, as was reported for packed beds [7]. A number of devices were proposed to ensure a uniform inlet velocity [5,8], which indeed increases the total pressure drop. 

Kang et al. have developed a multiple parallel channel ion exchange device in which each channel contained a stationary phase and its own dedicated conductivity detection electrode [192]. By reducing the channel width, these researchers... 

For spirals, Re is calculatnd as if it were a parallel-plate device tlie presence of the feed channel spacer is ignored,... 

Two-dimensional arrangements might be monolayers of clusters on a suitable substrate or two or more coupled ID arrays. While layers are accessible via self-assembly, LB, or electrodeposition, coupled arrays could be obtained by filling clusters into the parallel channels of a crystalline nanoporous solid. 2D networks of clusters might be precursors for simple neural networks, utilizing the Coulombic interaction between ballistic electrons in a 2D electron gas. This concept has been discussed by Naruse and in general introduces new possibilities for the interconnection approach in various fields, e.g. parallel processing and quantum functional devices. 

It is advantageous to choose a layout that yields more than one microchannel per device. An example with three parallel channels is displayed in Fig. lb. This ensures that an intact channel is available for the experiment, even if one (or two) of the channels are damaged by production errors. 

Hartwick (17) aligned uniformly sized fibers into a densely packed hexagonal array. The interstices between the fibers represented the flow channels. There was no transport between the channels. The performance of the device was low relative to its permeability. This is not unexpected A key property of a packed bed is the radial mass transfer, which evens out flow nonuniformities. Tto is not possible in a device consisting of parallel independent flow paths. In an array of circular parallel channels, the breakthrough time for an unretained sample is inversely proportional to the square of the diameter of the channel. To obtain a plate count of 10,000 plates, it would be necessary that the relative standard deviation of the channel diameter is under 0.5% (see also the footnote in Section 2.1.4). This is clearly a tall order. For retained peaks, similar demands would need to be placed on the uniformity of the stationary phase from channel to channel. 

FIGURE 44.10 To increase the throughput of the acoustic separation device, eight parallel channels were connected in a bifurcation network. The image shows two eight channel separators on a 3" silicon wafer. 

For mechanical lysis, nanostructured filter-Uke contractions are employed in microfluidic channels with pressure-driven cell flow. Prinz et al. utilized rapid diffusive mixing to lyse Escherichia coli cells and trap the released chromosome via dielectrophoresis (DEP). Kim et al. developed a microfluidic compact disk platform for mechanical lysis of cells using spherical particles with an efficiency of approximately 65 % however, this method is difficult to be apphed for single-cell analysis. Lee et al. fabricated nanoscale barbs in a microfluidic chip for mechanical cell lysis by shear and frictional forces. Munce et al. reported a device to lyse individual cells by electromechanical shear force at the entrance of 10 mm separation channels. The contents of individual cells were simultaneously injected into parallel channels for electrophoretic separation, which can be recorded by laser-induced fluorescence OLIF) of the labeled cellular contents. The use of individual separation channels for each cell separation eliminated possible cross-contamination from multiple cell separations in a single channel. 

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