Mimicking layer inversion in solid-liquid fluidized beds in narrow tubes

Abstract

This paper investigates experimentally and numerically the dynamics of solid particles during the layer inversion of binary solid-liquid fluidized beds in narrow tubes. Layer inversion can happen in solid classifiers and biological reactors, where different solid particles coexist and segregation by diameter and density occurs. The fluidized beds were formed in a 25.4 mm-ID pipe and consisted of alumina and aluminum beads with diameters of 6 and 4.8 mm,respectively. We placed initially the lighter particles on the bottom in order to force an inversion of layers, mimicking the layer inversion mechanism. In the experiments, we filmed the bed with a high-speed camera and tracked individual beads along images, while in numerical simulations we computed the bed evolution with a CFD-DEM (computational fluid dynamics -dis-crete element method) code. We found the distances traveled by individual particles during the inversion and the characteristic time for layer inversion.

Resolved CFD-DEM simulations of the hydraulic conveying of coarse grains through a very-narrow elbow

“…Interestingly, in all cases some particles did not reach the end of the vertical section. Instead, they fluctuated in that region rather than going straight to the outlet, in a behavior similar to those of fluidized beds [13,14].…”

“…The latter result is different from expected, and remains to be verified.Although appearing in flows with coarse grains in narrow and very narrow tubes, the granular structures were only fully scrutinized in a series of papers on fluidized beds. Cúñez and Franklin[2,13,14] investigated exper-imentally and numerically some of those features appearing in solid-liquid fluidized beds (SLFBs) with 3.2 ≤ D/d ≤ 5.3 (very-narrow case) and 2.50 ≤ S ≤ 3.69. The experiments made use of high-speed movies and the numerical simulations consisted of unresolved CFD-DEM computations.…”

“…different granular structures are observed[2,13,14].Ravelet et al[15] investigated experimentally the hydraulic conveying of coarse grains in horizontal pipes for 6.3 ≤ D/d ≤ 20 and 2.50 ≤ S ≤ 3.65, where S = ρ s /ρ, ρ s being the density of grains and ρ that of liquid. The authors characterized flow regimes based on visualization and pressure drop measurements, and found that the hydraulic gradient decreases with the particle size, different from commonly reported for vertical conveying.…”

Study on Characteristics of Particle Dynamics with Coarse Particles in Vertical and Inclined Pipeline

“…The particles transported by deep-sea mining pipelines are coarse. Coarse particles transported by pipeline means D/d ˂ 10 [11] ,where D and d mean the pipeline and particle diameter, respectively. Since the general CFD-DEM method requires a particle size smaller than the mesh size, it is difficult to solve the problem of coarse particle transport.…”

Miniaturized gas–solid fluidized beds

“…This is a characteristic of high confinement, and appears only in the very-narrow case. Later, we [56] investigated the segregation and the inversion of granular layers in the case of beds consisting of bidisperse mixtures. We found the trajectories of individual particles and the characteristic times for inversion in the verynarrow case, showing that the network of contact forces and confinement greatly affect layer inversion.…”