Showing papers by "Miryan Cassanello published in 1996"

Flow structure of the solids in a 3‐D gas–liquid–solid fluidized bed

Abstract: Local and macroscopic solids flow structure and kinematics in a 3-D gas–liquid–solid fluidized bed were studied using a noninvasive radioactive-particle tracking (RPT) technique. Based on the multisite detection of γ radiations emitted from a single radiolabeled tracer particle freely moving in the fluidized bed, RPT permitted to obtain fast sampling of 3-D trajectories of the tracer, whose physical properties were similar to those of the solids inventory. These trajectories showed the detailed motion sequences of the solid particles as entrained in the bubble wakes, fluctuating randomly or sinking deterministically in the liquid–solid emulsion. Based on measurements done in the vortical-spiral flow regime, the dynamic solids flow structure inside a three-phase fluidized bed can be viewed as a three-zone core–annulus–annulus structure: (1) a central fast-bubble flow region with the particles swirling upward; (2) a vortical flow region around the velocity inversion point with the particles momentarily captured in emulsion vortices; and (3) a relatively bubble-free descending flow region where the particles spiral down between the velocity inversion point and vessel walls. Our solids flow structure of dense fluidized beds are similar to the flow structure of liquid and/or solid in lean fluidized beds (observed through laser sheeting imaging). Measured distributions of local ensemble-averaged particle velocities and turbulence intensities were consistent with the existence of a toroidal recirculatory solids flow pattern in the bed. Measured mean circumferential ensemble-averaged radial velocity was essentially zero throughout most of the bed. The solids flow turbulence field was nonisotropic, as radial turbulence intensities were generally lower than longitudinal turbulence intensities.

Gas-liquid mass transfer in high pressure trickle-bed reactors: Experiments and modelling

Abstract: Gas-liquid interfacial areas a and volumetric liquid-side mass-transfer coefficients kLa are experimentally determined in a high pressure tri reactor up to 3.2 MPa. Fast and slow absorption of carbon dioxide in aqueous and organic diethanolamine solutions are employed as model reactions for the evaluation of a and kLa at high pressure, and various liquid viscosities and packing characteristics. A simple model to estimate a and kLa for the low interaction regime in high pressure trickle-bed reactors is proposed.

General criteria to analyze the role of mass transfer and hydrodynamics in trickle‐bed reactors

Abstract: General simple criteria to predict and analyze the influence on trickle-bed reactors behavior of three phenomena, namely, plug flow deviations, external wetting efficiency and external mass transfer resistance, are developed. Criteria predictions are compared with results arising from a comprehensive mathematical model widely employed to describe trickle-bed reactors behavior and with other particular criteria reported in the literature. Present criteria applications to different sets of experimental data exemplify their practical utility for various actual situations and verify their validity. Besides, they constitute simple tools to diagnose detrimental effects on trickle-bed reactors operation.