Streamline mixing

A tubular reactor in which the fluid flow is laminar is regarded as a non-ideal reactor, as discussed in Section 3.2.2. Laminar flow is the flow pattern in which the fluid elements move in streamlines in an orderly manner and no two fluid elements moving in two different streamlines mix with each other. Thus, the fluid elements mix neither in the axial direction nor in the radial direction. This pattern of fluid flow is called fully segregafed flow. Laminar flow of fluid in a tubular vessel is depicted in Figure 3.64. 

Certain hydrodynamical problems, as well as mass-transfer problems in the presence of surface-active agents, have been investigated theoretically under steady-state conditions (L3, L4, L10, R9). However, if we take into account the fact that in gas-liquid dispersions, the nonstationary term must appear in the equation of mass- or heat-transfer, it becomes apparent that an exact analysis is possible if a mixing-contacting mechanism is adopted instead of a theoretical streamline flow around a single bubble sphere. 

The double integral in Equation (8.4) is a fairly general definition of the mixing-cup average. It is applicable to arbitrary velocity profiles and noncircular cross sections but does assume straight streamlines of equal length. Treatment of curved streamlines requires a precise and possibly artificial definition of the system boundaries. See Nauman and Buffham. ... 

Fig. 6. (a) Schematic view of an extruder channel with an undulating baffle, (b) B, C, D Steady flow streamlines with and without baffles for initial condition A. E, F Mixing in a cavity flow with an oscillating baffle. The upper plate moves with a steady velocity while the lower plate with the baffle undergoes linear oscillatory motion (Jana, Tjahjadi, and Ottino, 1994). 

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