Configurations, mixed flow

A model of a reaction process is a set of data and equations that is believed to represent the performance of a specific vessel configuration (mixed, plug flow, laminar, dispersed, and so on). The equations include the stoichiometric relations, rate equations, heat and material balances, and auxihaiy relations such as those of mass transfer, pressure variation, contac ting efficiency, residence time distribution, and so on. The data describe physical and thermodynamic properties and, in the ultimate analysis, economic factors. 

Numbering-up can be performed in two ways (Figure 1.4). External numhering-up is referred to as the connection of many devices in a parallel fashion [8] (a similar, but less elaborate, definition was already provided in [9, 10] see also [11] for a realized industrial example). A device in the sense as it is used here is defined as a functional element, e.g. a micro-mixing flow configuration such as an interdigital... 

We focus attention in this chapter on simple, isothermal reacting systems, and on the four types BR, CSTR, PFR, and LFR for single-vessel comparisons, and on CSTR and PFR models for multiple-vessel configurations in flow systems. We use residence-time-distribution (RTD) analysis in some of the multiple-vessel situations, to illustrate some aspects of both performance and mixing. 

Classical chemical reaction engineering provides mathematical concepts to describe the ideal (and real) mass balances and reaction kinetics of commonly used reactor types that include discontinuous batch, mixed flow, plug flow, batch recirculation systems and staged or cascade reactor configurations (Levenspiel, 1996). Mixed flow reactors are sometimes referred to as continuously stirred tank reactors (CSTRs). The different reactor types are shown schematically in Fig. 8-1. All these reactor types and configurations are amenable to photochemical reaction engineering. 

Since gas causes most of the mixing in three-phase reactors, its distribution is, of course, very important. For small-diameter columns, the nature of a gas distributor is known to have a significant effect on RTD. Similar information on large-diameter columns is presently unavailable. For reactor scaleup purposes, such information is desirable. Studies should consider various reactor configurations and flow regimes. 

Depending on how the drying medium and droplets produced by the atomizer are contacted, three basic air-droplet contacting configurations can be identified, i.e., cocurrent flow, countercurrent flow, and mixed flow. 

Control system strategies are the same for both types. Diaphragm-cell evaporators may contain four effects and are more likely to have a mixed-flow configuration. Output is usually controlled by the primary steam flow, and the density control system can switch from startup to normal operation in the manner described above. 

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