Experimental Study on the Hydrodynamic Characteristics and Flow Structures of Slugging Fluidized Bed with Electrical Capacitance Volume Tomography Measurement

Slugging fluidization, which mainly occurs in the bed with large height-to-diameter aspect ratio, represents one of the major gas–solid fluidization regimes. There are two different kinds of axisymmetric slugs based on the specific particle size employed, i.e., round-nosed slugs and square-nosed slugs. Round-nosed slugs occur when fine particles are used as the fluidized particles. Square-nosed slugs occur when coarse particles are used in a small diameter bed, resulting in significant particle bridging and “locking” effects between particles and the bed wall. For both kinds of slugging fluidized bed, the friction between the solid particles and the wall plays a significant role to the pressure drop through the bed. Due to the limited availability of the experimental measurement methods, characterization of the slugging phenomena was mainly conducted through visualization by measuring the slug rise velocity, slug length, inter-slug spacing, and slug frequency. Pressure drop measurements were normally used to reconstruct the cross-sectional average gas-solids volume fraction profiles in the slugging fluidized bed. These methods normally can’t capture the detailed characteristics of the slugging fluidized bed. For example, due to the difficulties of identifying the contribution portion of friction to the pressure drop of the bed under different conditions, the pressure-drop derived solids volume fraction in the solids-dense region is generally larger than the actual value. With recent advances in the sensor development and image construction techniques for the electrical capacitance volume tomography (ECVT) for 3-D multiphase flow imaging, it is now possible to use the ECVT to obtain the reconstructed 3-D image of multiphase flow phenomena in real time. In this study, three-dimensional ECVT sensors were applied to imaging the flow structures of gas–solids slugging fluidized beds. The detailed 3-D images were obtained and analyzed to reconstruct the real time 3-D gas-solids volume fraction profile of the bed. The entire evolving process of the slugging fluidization from its formation to breakage was analyzed. The solids volume fraction profiles of the slugging bed were plotted under different gas velocity conditions. Particles with different sizes were used in the experiments to investigate the different hydrodynamic characteristics of round-nosed and square-nosed slugging beds.