(163i) Relationship Between Structure and Transfer Coefficients in Fast Fluidized Beds--a Theoretical Analysis

In the fast fluidized bed there are non-uniformity of radial and axial solids distributions in macroscopic view; meanwhile there are non-uniformity of distributions of dispersed phase and cluster phase in microscopic view. The clusters behave in the way of sometimes aggregating and sometimes dispersing and their shape and size are different and change frequently. Furthermore the distributions of velocities of the gas and particles are also heterogeneous. It can conclude that in fast fluidized bed there exist heterogeneous structures in both macro-scale and micro-scale.

Both experimental results and theoretical analysis have shown that there are significant effects of the bed structures on the momentum transfer behavior. For example, under same operating conditions of gas velocity, solids flow rate, and averaged voidage, the drag coefficient of interaction between gas and particle is 18.6 for the homogeneously distributed particles, and while the the drag coefficient of interaction between gas and particle is 2.85 for the heterogeneously distributed particles. It can be imagined that there also are significant effects of the bed structures on the mass and heat transfer behaviors. In the present work a theoretical analysis on the relationships between local bed structure and momentum, mass, and heat transfer coefficients, is given. The effects of aggregating and dispersing of the particles on the mass and heat transfer are discussed. The theoretical prediction was compared with the experiment data in the literature, The theoretical values are in good agreement with the experimental data..

Keywords: Structure; Mass transfer; Heat transfer; Fluidization; Multiphase flow;

Particle