Studies On The Novel Two-fluid Model For Bubbling And Turbulent Fluidized Beds

The enlargement and enhancement of fluidized bed reactor represents the tendency of current technology development. Fluidization hydrodynamics is the basis of the reactor design and scale-up. However the present gas-solid two fluid model (TFM) based on kinetic theory of granular flow (KTGF) seems incapable of scale-up simulation for bubbling and turbulent fluidized bed. The hydrodynamics in bubbling fluidized beds and turbulent fluidized beds were studies by combination experimental measurements and computational fluid dynamics simulation. Novel two-fluid hydrodynamic models are proposed in this work for fluidized beds simulation and scale-up. The following aspects were discussed in this thesis.1. Measurements of hydrodynamic parameters in bubbling and turbulent fluidized beds. Solid fraction in different size fluidized beds were measured by optical fiber probe under three different superficial gas velocities and three different static bed heights at different axial levels. The experimental results showed that the lateral distribution of solid fraction is core-annulus and the operating conditions can influence the shape of the axial solid fraction profiles.2. A novel two-fluid hydrodynamics model for bubbling fluidized beds. This work proposes an analogous research program, according to the analogies in flow regime and mechanism between gas-solid bubbling fluidized bed and gas-liquid bubble column that aims to develop a unified two phase hydrodynamic model applicable both to them for mathematical scale up of the reactors. The research includes a complete description of the constitutive relationship for inter-phase forces around the bubbles, a comprehensive investigation of correlations for bubble and emulsion phase properties, and an in-deep analysis of the mechanism of radial non-uniformity in fluidized bed. The model is verified through comparison simulated results with experimental data of both Geldart A and B particles. The model conducted on course grid which shows more potential for the simulation of commercial fluidized equipments.3. A novel two-fluid hydrodynamics model for turbulent fluidized beds. A novel two-fluid hydrodynamics model that undergo change of the continuous phase is proposed to simulate the coexisting regions, the bottom dense, bubbling region and the dilute, dispersed flow region in turbulent fluidized beds. In the bubbling region, the radial non-uniformity is mainly determined by the forces balance among lift force, turbulent dispersion forces and wall force that acted on bubbles, while in the dispersed region, the radial non-uniformity is mainly determined by the forces balance among lift force and turbulent dispersion forces that acted on clusters.A characteristic distinguishing from previous studies of this thesis is that we highly stressed the role of transverse forces which determine the movement of bubbles or cluster in the radial direction, thereby determining the distribution of the porosity in the radial direction of the beds. Such radial uneven distribution is the momentum source that drives two-phase flow, thus the lateral force constitutive relations occupies an important position in the model.