INFLUENCE OF BED DIAMETER ON HYDRODYNAMICS

Scaling has many useful applications. The dynamic characteristics of different bed designs can be quickly compared. The influence of bed diameter on hydrodynamic behavior can be studied by the use of several different size models. The models allow easy experimental examination of existing operating characteristics. The beds also can be used to quickly confirm the influence of proposed modifications. Since the models usually operate at ambient conditions, it is possible to instrument them to observe detailed behavior. This allows a better understanding of the fundamental physics as well as the identification of hydrodynamic factors needed for proper correlation of performance. 

Noymer, P. D., Hyre, M. R., and Glicksman, L. R., The Influence of Bed Diameter on Hydrodynamics and Heat Transfer in Circulating Fluidized Beds, Fluidization and Fluid-Particle Systems, AIChE, pp. 86-90 (1995)... 

Noymer PD, Hyre MR, Glicksman LR. The influence of bed diameter on hydrodynamics and heat transfer in circulating fluidized beds. Fluidization and Fluid-Particle Systems, AIChE, 1995, pp 86-90. 

As fluidized beds are scaled up from bench scale to commercial plant size the hydrodynamic behavior of the bed changes, resulting, in many cases, in a loss of performance. Although there have been some studies of the influence of bed diameter on overall performance as well as detailed behavior such as solids mixing and bubble characteristics, generalized rules to guide scale-up are not available. The influence of bed diameter on performance will differ for different flow regimes of fluidization. 

Werther J. Influence of bed diameter on the hydrodynamics of gas fluidized beds. AIChE Symposium Ser 70(141) 53, 1974. 

Figure 20. Use of scale models with different bed diameters to simulate the influence of diameter on the hydrodynamics of a hot commercial reactor.

Packed bed reactors [51] incorporate beads, and the presence of these solid materials in the analytical path also has a beneficial influence on the flow pattern, reducing sample broadening and, hence, sample dispersion. However, hydrodynamic pressure tends to be increased, especially when small particles and/or particles with heterogeneous sizes are used. Single bead string reactors [5] were proposed to circumvent this drawback. These reactors utilise large (particle diameters about 70% or the tube inner... 

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