Question

Fluidised beds are formed when the

• A. Fluid friction is zero
• B. Gravity force is less than the fluid friction
• C. Pressure forces equal to gravity forces
• D. Pressure force is greater than the gravity force

Hint:

Fluidisation occurs when upward drag force of the fluid becomes sufficient to suspend solid particles.

Answer 1

The Correct Option is B

A fluidised bed is formed when a fluid flows upward through a bed of solid particles. At low velocity, the particles remain fixed. As the fluid velocity increases, the upward drag or fluid friction force on particles increases. When the upward fluid force becomes sufficient to support the particles, the bed starts behaving like a fluid. At this condition, particles become suspended and fluidisation begins. According to the given answer key, fluidised beds are formed when: \[ \text{Gravity force is less than the fluid friction}. \] This means the upward fluid friction is strong enough to overcome the tendency of particles to remain settled due to gravity. Therefore, the correct answer is: \[ \text{Gravity force is less than the fluid friction}. \]