The bubble characteristics in a 3-D cylindrical fluidized bed have been investigated both experimentally and numerically. Experiments were performed on a 0.1 m diameter fluidized bed, with alumina oxide particles (diameter ~1 mm) as a fluidizing material. Measurements were done at a spatial resolution of 1 mm and a temporal resolution of 1000 cross-sectional images per second, using an ultrafast electron beam X-ray computed tomography (XRT) setup (Fischer and Hampel 2010). A two-fluid model using kinetic theory of granular flow (Verma et al., 2013) was used to predict the bed dynamics numerically. The equivalent bubble diameter as a function of height is in close agreement with Darton et al. (1977) and Werther (1975) correlations. The bubble size distribution predicted from simulations is broader compared to experiments. Both the bubble rise velocity and the bubble size increase with increase in excess gas velocity. The experimental measurements and simulation predictions are in fair agreement with the Hilligardt and Werther (1986) correlation.@en

Bubble characteristics in a three-dimension gas-fluidized bed (FB) have been measured using noninvasive ultrafast electron beam X-ray tomography. The measurements are compared with predictions by a two-fluid model (TFM) based on kinetic theory of granular flow. The effect of bed material (glass, alumina, and low linear density polyethylene (LLDPE), dp ~1 mm), inlet gas velocity, and initial particle bed height on the bubble behavior is investigated in a cylindrical column of 0.1-m diameter. The bubble rise velocity is determined by cross correlation of images from dual horizontal planes. The bubble characteristics depend highly upon the particle collisional properties. The bubble sizes obtained from experiments and simulations show good agreement. The LLDPE particles show high gas hold-up and higher bubble rise velocity than predicted on basis of literature correlations. The bed expansion is relatively high for LLDPE particles. The X-ray tomography and TFM results provide in-depth understanding of bubble behavior in FBs containing different granular material types.@en

It is well known that hydrodynamics observed in large scale gas-solid fluidized beds are different from those observed in smaller scale beds. In this article, an efficient two-fluid model based on kinetic theory of granular flow is applied, with the goal to highlight and investigate hydrodynamics differences between three-dimensional fluidized beds of diameter 0.10, 0.15, 0.30, 0.60, and 1.0 m, focusing on the bubble and solids flow characteristics in the bubbling regime. Results for the 0.30 m diameter bed are compared with experimental results from the literature. The bubble size evolution closely follows a correlation proposed by Werther for small beds, and a correlation proposed by Darton for sufficiently large beds. The bubble size increases as the bed diameter is increased from 0.10 to 0.30 m, and remains approximately constant for bed diameters from 0.30 to 1.0 m. Concurrently, an increase in bubble rise velocity is observed, with a much high bubble rise velocity in the largest bed of diameter 1.0 m due to gulf stream circulations. The dynamics in shallow and deep beds is predicted to be different, with marked differences in bubble size and solids circulation patterns.@en

We apply a recently developed two-fluid continuum model (TFM) based on kinetic theory of granular flow (KTGF) in three dimensional cylindrical coordinates, to investigate bubble formation through a single central orifice in a gas-solid fluidized bed. A comprehensive study for Geldart D type particles, revealing the influence of particle diameter, jet injection flow rate, and bed size on bubble characteristics have been investigated. At a given gas injection flow rate, the bubble diameter continuously increases while gas leakage from the bubble to the emulsion phase decreases with time. With increasing particle diameter, leakage fraction increases and hence a smaller bubble diameter is predicted. These results are consistent with DPM simulations, experimental results and approximate bubble formation models reported previously in the literature.@en

A highly efficient numerical scheme has been incorporated to solve a traditional two-fluid model for dense gas-solid flow in large scale fluidized beds. Difficulties associated with the numerical solution and boundary condition enforcement especially in the azimuthally direction and at the axis of the cylindrical domain are discussed in detail. Higher order discretization schemes with deferred correction approach have been implemented for the convection terms. The p- ε algorithm (Van der Hoef et al., 2006) has been implemented to deal with densely packed regions in the fluidized bed. A modified SIMPLE algorithm is used to solve the pressure and volume fraction corrections, and a projection method is used to obtain solutions of the momentum equations. The resulting semi-implicit method allows for using larger time steps and produces accurate results in a stable and efficient manner. Numerical tests on bubbling fluidized beds are undertaken and compared with experimental data reported by Laverman et al., 2012. The simulation results are found to be in good agreement. In addition a comparative study has been performed quantifying the effects of grid size, flux limiters, frictional model and coefficient of restitution.@en

We apply a two-fluid model to investigate hydrodynamic differences in a three-dimensional fluidized bed operating at pressures of 1, 2, 4, 8, 16, 20, and 32 bar. The simulation results are compared with experimental results from the literature and show very good agreement. A detailed investigation is carried out on pressure fluctuations, porosity distribution, and bubble and solids flow characteristics. At high pressure, the porosity distribution is homogeneous and fluidization is smooth. The bubble size depends upon the location in the 3D bed, showing different trends at different pressures. The average bubble size is reduced with an increase in pressure, caused by a difference in coalescence and splitting of bubbles. An initial increase in pressure from 1 to 2 bar shows an increase in bubble rise velocity, but a further increase in pressure causes bubbles to rise more slowly. High up-flow of solids is observed in the center at high pressures, with pronounced differences in solids circulation vortices.@en

The effect of the bed diameter on the gas-solids flow characteristics inside a cylindrical fluidized bed is investigated numerically using a two-fluid model based on the kinetic theory of granular flow. Particle bed diameters of 0.10, 0.15, 0.30 and 0.60 m are studied, containing particles of 1.1 mm diameter and a density of 800 kg/m3 (Geldart B), using an inlet gas velocity of 2.5Umf. The equivalent bubble diameter shows an increasing trend with height in the bed and bed diameter. Slugging behavior is observed in a smaller bed and/or above a bed height of approximately twice the bed diameter. The porosity near the axis is higher for a smaller bed and gradually decreases for a larger bed. Different particle circulation patterns are observed for different bed sizes. The center of circulation vortex at the bottom for a smaller bed lies approximately at r/R = 0.5 and this center is shifted to r/R = 0.8 for a larger bed. The upper particle circulation obtains a more elongated shape for a smaller and deeper bed in comparison to a larger bed diameter. The particle flow characteristics are nearly the same for the 0.30 and 0.60 m diameter beds, irrespective of the difference in bubble size. This shows that the bed size effect levels off beyond a 0.30 m diameter column for Geldart B particles.@en