Reactor design turbulent transport

In the applications that have been discussed here, high rates of transport have, somewhat paradoxically, favored attainment of conditions under which analyses neglecting transport effects can be applied. The rapid transport helps to achieve conditions of uniformity, under which transport no longer is significant, and effects of finite-rate chemistry can be studied. This same kind of situation prevails in various other experiments, such as those employing a suitably designed turbulent-flow reactor [18], [19], [20]. In... 

When two or more phases are present, it is rarely possible to design a reactor on a strictly first-principles basis. Rather than starting with the mass, energy, and momentum transport equations, as was done for the laminar flow systems in Chapter 8, we tend to use simplified flow models with empirical correlations for mass transfer coefficients and interfacial areas. The approach is conceptually similar to that used for friction factors and heat transfer coefficients in turbulent flow systems. It usually provides an adequate basis for design and scaleup, although extra care must be taken that the correlations are appropriate. 

The production of turbulence is maximum close to walls, where both shear rate and turbulent viscosity, ut, are high. In pipe flow, the maximum is close to y+ = 12. A proper design of a chemical reactor for efficient mixing at low Re should allow the generated turbulence to be transported with the mean flow from the region where it is produced to the bulk of the fluid where it should dissipate. 

Chemical reactors, particularly for continuous processes, are often custom designed to involve multiple phases (e.g., vapor, liquid, reacting solid, and solid catalyst), different geometries (e.g., stirred tanks, tubular flows, converging and diverging nozzles, spiral flows, and membrane transport), and various regimes of momentum, heat, and mass transfer (e.g., viscous flow, turbulent flow, conduction, radiation, di sion, and dispersion). There... 

The current approach that best meets the need of industry is the E-E approach with k-e modeling for the turbulence. This provides details about the flow and related transport phenomena that cannot be obtained by experiments, let alone for a production reactor where experiments are, for obvious reasons, not allowed or at best rather restricted. It, however, has also limitations and will not provide answers without uncertainty margins. For instance, coalescence and breakup are notoriously difficult to model and have a large uncertainty. Moreover, the liquid is in most cases treated as a Newtonian liquid. A different rheology is difficult to incorporate [58]. Similarly, the effect of surfactants that are omnipresent in the bioreactors is hard to incorporate [59]. For that, much research is still needed. Nevertheless, CFD is the way forward and offers an important addition to the tools and techniques available to designers and operators. 

Transport reactor, 72 Trickle-bed design of, 437, 441 flow regimes in, 432 mass transfer in, 236 Turbulent fluidization, 414 Two phase models, 407 Two-step kinetic model, 67... 

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