Introduction

The flow characteristics of solid particles in a gas–solid suspension vary significantly with the geometric and material properties of the particle. The geometric properties of particles include their size, size distribution, and shape. Particles in a gas–solid flow of practical interest are usually of nonspherical or irregular shapes and polydispersed sizes. The geometric properties of particles affect the particle flow behavior through an interaction with the gas medium as exhibited by the drag force, the distribution of the boundary layer on the particle surface, and the generation and dissipation of wake vortices. The material properties of particles include such characteristics as physical adsorption, elastic and plastic deformation, ductile and brittle fracturing, solid electrification, magnetization, heat conduction and thermal radiation, and optical transmission. The material properties affect the long– and short–range interparticle forces, and particle attrition and erosion behavior in gas–solid flows. The geometric and material properties of particles also represent the basic parameters affecting the flow regimes in gas–solid systems such as fluidized beds.

In this chapter, the basic definitions of the equivalent diameter for an individual particle of irregular shape and its corresponding particle sizing techniques are presented. Typical density functions characterizing the particle size distribution for polydispersed particle systems are introduced. Several formulae expressing the particle size averaging methods are given. Basic characteristics of various material properties are illustrated.

Particle Size and Sizing Methods

The particle size affects the dynamic behavior of a gas–solid flow [Dallavalle, 1948]. An illustration of the relative magnitudes of particle sizes in various multiphase systems is given in Fig. 1.1 [Soo, 1990].