Introduction to Particulate SolidsThe most important characteristics of a particle are its composition, size and shape. Composition of the particle helps in determining the Density as well as conductivity. It is stated that composition must be properly uniformed. Sometimes particle may be porous or may contain continuous matrix containing other material in it. Particle size is considered as an important characteristic since it affects the properties such as surface per unit volume and the rate of settling the particle in the fluid. The shape of the particle may be regular or irregular |
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Regular particle may be Spherical or Cubical. Irregular particle may consist of a broken glass. Regular shapes are defied by mathematical equation while irregular shapes are defined in terms of characteristic of a regular shape particle. On the industrial scale, usually bulk quantity of materials is handled. Sometimes it is necessary to define the system as a whole. When the particle size of whole mass is needed to know. Then average mean size of particle is calculated. This mean size of particle represents the behavior of particulate mass as whole. Frequent operation of particle includes storage in hopper, flow through pipes and Orifices. Sometimes it is necessary to reduce the size of particles. Sometimes it is desired to mix two or more solids. Sometimes the mixture of particle is to be separated in to its own component or according to the sizes of the particle. The fluid surrounding the particle can be of little significance in some cases, and at other times it can have a dominating effect. In the sedimentation process, particles are completely surrounded by fluids and are completely allowed to move freely relative to other particles. |
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Characterization of Particles
Single Particles
Sphere is the simplest shape of particle. Because of its symmetry. No question of orientation arises when the particle is symmetric. It shows exactly the same from whatever angle it is viewed and behaves in the same manner in the fluid. This particle has the distinction over other particle. Usually, size of particle with irregular shape is defined in terms of size of an equivalent sphere. According to the particle selected, the particle is represented by a sphere of different size.
Size of Equivalent Sphere
- Some of the sizes of equivalent sphere are as follows
- The sphere having the same volume as the particle
- The sphere having the same surface area as the particle
- The sphere having the same surface area per unit volume as the particle
- The sphere having the same area as the particle when projected on to a plane perpendicular to its direction of motion
- The sphere having the same projected area as the particle, when seen from above or when lying in the position of its maximum stability.
- The sphere which passes through the same size of a square aperture as the particle.
- The sphere having the same settling velocity as the particle in the specified fluid.
Feret's Statistical Diameter
It is the mean distance between the two parallel lines which are tangent to the particle as well in an arbitrarily fixed direction. It is irrespective of the orientation of each particle coming up for inspection.
Formula
Ψ= Surface area of sphere of same volume as particle/Surface area of particle
Other Properties of Solids
Other properties of particle which are also considered are as follows.
- Whether a particle is crystalline or amorphous
- Whether a particle is porous or not
- Surface properties of a particle such as its roughness and presence of adsorbed films.
- Hardness is also considered when the particle is subjected to heavy loadings.
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