Optimization channel

Scale-up of microchannel reactors is based on using the optimal channel dimensions rather than seeking the smallest or the largest microchannel. In some cases, the channels may range from 100 pm in hydrauhc diameter to a few millimeters. The classification of a rigorous size range to designate a reactor as microchannel is not necessary. 

As demonstrated in the case study, an optimal channel depth exists where the specific rate is at a maximum. Designing the screw at this maximum specific rate is typically the desire. The parabolic shape of the specific rate curve shown in Fig. 13.10 was caused by the rotational rate increasing iineariy with increasing channel depth see Eq. 7.58. This increase in rotational rate causes the overall rate to increase. The pressure flow increases with the cube of the channel depth, and... 

An unexpected key benefit from the use of microreactors has been the detailed flow information that is available from their construction. To build optimized channel structures detailed models of the devices have been developed. These models offer the potential to use the information as the basis for reactor modeling. The result is that with detailed reactor models and precise composition measurements from on-line analysis the rate expressions for the chemistry can be extracted from the laboratory data. The potenhal of this is significant in that general laboratory data only gives a sense of what is happening whereas now... 

In lead optimization using conventional batch technology, irrespective of whether parallel or iterative mode is chosen, validation and optimization of reactions tends to be one of the major rate-limiting steps. Based on the model described in Fig. 14.5, however, it can be seen that if the biological assay was replaced by a chemical assay and the conditions not the reagents are varied, then an auto-optimization could be carried out. Replication of the optimized channel as a parallel bundle could then provide a means of amplifying the amounts of material generated. 

After CL detection was successfully introduced to the microchip and optimal channel design and reaction conditions were obtained, it was used for high-sensi-tivity detection, especially for single cells analysis. Zhao et al. [73] first reported that CL detection with microchip electrophoresis was used to determine the intracellular content of glutathione in single human red blood cells. CL detection showed about 100 times more sensitivity than LIP detection for single cell analysis. 

FIGURE 10.14 Typical commercial net-type spacers. (Reprinted from /. Membr. ScL, 62, Da Costa, A.R., Fane, A.G., Fell, C.J.D., and Franken, A.C.M., Optimal channel spacer design for ultrafiltration, 275-291, Copyright 1991, with permission from Elsevier.)... 

Da Costa AR, Fane AG, Fell CJD, Franken ACM. Optimal channel spacer design for ultrafiltration. J. Membr. Sci. 1991 62 275-291. 

Great efforts have been undertaken to describe the intricate geometry of river networks [363]. In Chap. 6 we illustrated some models, such as the Peano network, which resembles fractal river basins. Another well-known structure that was proposed to describe better the evolution and formation of river basins and that agrees with most of the observations is the Optimal Channels Network (OCN) model, based on some optimization principles that minimize the energy expenditure by the net-... 

Manifold optimisation is a compromise between pressure drop and porous volume, on which the channel diameter has opposite effects. This leads to an optimal channel diameter distribution with scaling laws, while the lengths are determined by the speciflcation of the outlet surface. For distributors with a dichotomic structure, such as that shown, and in conditions of laminar flow, the main theoretical limitations of this treatment are that it neglects inertial effects, and thus applies only at very small Reynolds numbers. In addition to the use of this design method in manifolds for micro-reactors, the research team in France has identified interest in several other areas, including ... 

The improvement of heat transfer by optimized channel and wall geometries and the choice of best-suited materials contribute to the enhancement of process speed and to a better control of selectivity. Adapted selectivity can be achieved by realizing well-defined temperature proto-... 

Depending on the size of the cell and the materials used in the separators, the optimal type of channel design, channel width and depth, and the wettability of the surfaces are different. Additionally, the current density and gas flow rates also affect the design. To establish general guidelines for optimal channel designs for these and related parameters, more research is still necessary. This section will present some results of the water behavior in cells and the characteristics of porous separators. 

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