Generalized flow regime diagram of fluidized beds based on the height to bed diameter ratio

摘要

This paper describes a comprehensive experimental analysis that reexamines Geldart's classification. Geldart's classification defines four types of materials which differ by the cohesion forces between particles. A system containing fluidized beds of four pipe diameters and fully controlled by LabVIEW was developed and constructed. A fluidization test was performed automatically by small increase of the air velocity and measuring the pressure drop over the bed. For each test the fluidization curve is recorded and minimum fluidization, bubbling and slugging velocities are defined. It is well established that cohesion and gravity forces affect the fluidization behavior of numerous materials. Based on our experimental and theoretical study, we show that group D particles for height to bed diameter ratios above four start to be fluidized by slugging. Group B particles, however, does not always start fluidization in the bubbling regime. Rather in height to bed diameter ratios above ten they behave like those of group D. Particles of group A start to fluidize first by increasing bed volume, and later by bubbling and finally slugging may be reached. We further found that the bed height to diameter ratio affect the minimum bubbling and slugging velocities. On this basis, we developed a generalized flow regime diagram of the Reynolds number as a function of the Archimedes number to describe the fluidization state. According to this diagram, various materials can be accurately classified by both the Archimedes number and the height to bed diameter ratio.