Particle Technology: Fluidization

Front

What is fluidization?

Back

A fluid is passed through a solid material at high enough velocities to suspend the solid and cause it to behave as though it were a fluid.

Front

What is the mechanism of fluidization in a packed bed?

Back

A fluid enters from the bottom at a high enough velocity and flows upward through the particles, pushing them upward and causing the bed to expand and become fluidized.

Front

List some uses of fluidization.

Back

Chemical reactors, heat exchangers, drying, coating, solidification/granulation, growth of particles, adsorption/desorption.

Front

What are the advantages of fluidization?

Back

1. Liquid-like behavior is easy to control and automate. 2. Rapid mixing, uniform temperature, and concentration. 3. Responds slowly to rapid temperature changes. 4. Useful for large and small operations. 5. High heat and mass transfer rates require smaller surfaces.

Front

What are the disadvantages of fluidization?

Back

1. Bubbling beds of fine particles are difficult to predict. 2. Rapid mixing causes non-uniform residence times for continuous flow reactors. 3. Particle break-up may occur. 4. Pipe and wall vessels erode due to particle collisions.

Front

What is particulate fluidization?

Back

Also known as non-bubbling fluidization, it starts with the gentle oscillating motion of some particles in the bed as fluid velocity increases.

Front

What factors affect the variability of particulate fluidization?

Back

1. Liquid flow within the packed bed is not perfectly homogeneous. 2. Particle-particle interactions create zones with varying resistance to flow.

Front

Describe the pressure drop vs. fluid velocity relationship for packed and fluidized beds.

Back

A linear relationship is observed until the bed starts to expand. As the bed expands and porosity increases, the slope diminishes, and the pressure drop reaches a maximum before stabilizing.

Front

What is the minimum bubbling velocity (U_mb)?

Back

The upper limit of gas velocity for particulate expansion, affected by factors like the nature of the distributor and the presence of obstructions in the bed.

Front

What is Geldart's powder classification?

Back

It categorizes powders based on their fluidization behavior, including whether the gas flow rate is increased, the rising velocity of bubbles, and the adhesive forces between particles.