How Mixing Affects Reaction in Common Reactor Geometries

2 How Mixing Affects Reaction in Common Reactor Geometries 

1 Pipes. The simplest mixed chemical reactor is a pipe with reactant injectors at one end. The reactants mix as they flow toward the outlet, forming a tubular reactor. There are two measures of mixing in a pipe (1) the degree of uniformity of the average concentration in the radial direction, and (2) the mean square of the level of concentration fluctuations (referred to as segregation) at various locations across the pipe. 

Pipe reactors can be operated in laminar or turbulent flow. In laminar flow radial diffusivity is molecular only, which is very slow, particularly if the viscosity is high. In turbulent flow the radial fluctuating velocity component produces the radial turbulent diffusivity which is much faster than molecular diffusivity. Many devices have been developed to promote fast radial mixing in laminar flow, such as static mixers, which are discussed below and in Chapter 7. Besides static mixers, a number of methods exist to promote faster radial mixing in turbulent flow, since even in turbulent flow it takes 50 to 100 pipe diameters to achieve 

Another type of tee mixer involves opposing flows of reactants with outflow through the side exit into a mixing pipe. One example is the impinging jet reactor used in reaction injection molding technology. The Tee mixer, which is frequently used for liquid-phase reactions, is easier to construct and maintain 

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