Multi-scale concept

The realization of complete bench-scale micro reactor set-ups is certainly still in its infancy. Nevertheless, the first investigations and proposals point at different generic concepts. First, this stems from the choice of the constructing elements for such set-ups. Either microfluidic components can be exclusively employed (the so-caUed monolithic concept) or mixed with conventional components (the so-called hybrid or multi-scale concept). Secondly, differences concerning the task of a micro-reactor plant exist. The design can be tailor-made for a specific reaction or process (specialty plant) or be designated for various processing tasks (multi-purpose plant). 

Figure 1.4 Micro mixers (laboratory scale) and micro structured mixers (pilot scale) close the gap with static mixers, yielding apparatus for a multi-scale concept. Today s microstructured devices achieve mixing at up to about 1 m3 fT1 liquid throughput [2, 64] (by courtesy of RSC and Chemical Engineering).

Compared with the multi-scale micro mixer-tube concept (see Section 4.1.6), the total-system approach is a true mono-scale solution, and may be even termed monolithic. Integration of sensing and controlling is facile owing to the high order and repetition of construction imits (plates). 

Albeit originally proposed for gas-solid fluidization, the concepts of structure resolution and compromise between dominant mechanisms embodied in the EMMS model can be generalized into the so-called variational multi-scale methodology (Li and Kwauk, 2003) and extended to other complex systems (Ge et al., 2007). One typical example out of these extensions is the Dual-Bubble-Size (DBS) model for gas-liquid two-phase flow in bubble columns (Yang et al., 2007, 2010). 

This section will first deal with the phases in particle-fluid two-phase flow by developing a mathematical model to quantify local hydrodynamic states. This analysis will reveal the insufficiency of the conditions for the conservation of mass and momentum alone in determining the hydrodynamic states of heterogeneous particle-fluid systems, and calls for a methodology different from what is used in analyzing dilute uniform flow. For this purpose the concept of multi-scale interaction between particles and fluid and the principle of energy minimization are proposed. 

Bauer, M. and Eigenberger, G. (1999), A concept for multi-scale modeling of bubble columns and loop reactors, Chem. Eng. ScL, 54, 5109-5117. 

One favored concept today is the deposition of nano-sized particles dispersed in a hydrophobic binder [52-56]. While the hydrophobic binder imparts basic hy-drophobicity to the fiber surfaces, i.e. 0y 90°, the inclusion of particles creates a multi-scaled surface topography in combination with the texture of yam and fabric. 

In the following we discuss in a general way the key concepts supporting the multi-scale model MEMEPhys . For full mathematioal details, the author invites the readers to refer to his group publications. " ... 

SMB is now accepted as a real production tool. For instance, the Belgium pharmaceutical company U.C.B. Pharma announced recently the use of SMB for performing multi-ton scale purification of an enantiopure drug substance. The concept of large-scale purification of enantiomers using chromatographic techniques has moved from a dream to a reality within the last few years. 

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