Understanding Minimum Fluidization Velocity and Types of Fluidization, Schemes and Mind Maps of Fluid Mechanics

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Fluidization

At certain Fluid velocity :

Fluidization of particles

begins

Fluidization

• (^) When a fluid flows upward through a packed bed of particles at low velocities, the particles remain stationary. As the fluid velocity is increased, the pressure drop increases (given by Ergun equation)
• (^) With further increases in velocity, the force of the pressure drop just equals the gravitational force on the mass of particles minus buoyant force.
• (^) Then the particles just begin to move, and this is the onset of fluidization or minimum fluidization. The fluid velocity at which fluidization begins is the minimum fluidization velocity vmf in m/s based on the empty cross section of the tower (superficial velocity).

Minimum Fluidization Velocity (v 0M

= Weight of bed per unit area of cross section – buoyant force of displaced fluid Pressure drop across the bed = ΔP = (g) (1-ε)(ρ p

• ρ) L At the beginning porosity ε = ε m => ΔP/L = (g) (1-ε m )(ρ p
• ρ) Substituting in Ergun Equation = (g) (π/4)D 2 (1-ε)ρ p L- m ρg / ρ p m= (π/4)D^2 (1-ε)Lρp

For fine particles with laminar region: When Rep> 1000

Types of Fluidization: The fluidization equation applies for liquids and gasses Appearance of beds fluidized with liquids and gasses is quite different Particulate Fluidization (liquid): large but uniform expansion of bed at greater velocities than v0M same average bed density