ANS:B - fluidisedbed

A fluidized bed is a type of reactor or dryer in which a bed of solid particles is made to behave like a fluid by passing gas or liquid upwards through the bed at a sufficient velocity to suspend the solid particles. In other words, the solid particles become buoyant and exhibit fluid-like behavior due to the upward flow of the fluidizing medium. Here's how a fluidized bed works and some key features:

1. Fluidization: When a fluid (gas or liquid) is passed through a bed of solid particles at a certain velocity, it exerts drag forces on the particles. At low fluid velocities, the solid particles are packed together, and the bed behaves like a solid. However, as the fluid velocity increases, the drag forces become strong enough to overcome the gravitational forces acting on the particles, causing them to become suspended and exhibit fluid-like behavior. This state is known as fluidization.
2. Uniform Mixing and Heat Transfer: In a fluidized bed, the suspended particles are in constant motion and undergo random mixing, leading to excellent mixing and homogeneity within the bed. This uniform mixing enhances heat and mass transfer between the solid particles and the fluidizing medium, making fluidized beds efficient for various processes such as drying, granulation, combustion, and chemical reactions.
3. Controlled Temperature: Fluidized beds offer good control over temperature due to the efficient heat transfer between the solid particles and the fluidizing medium. This makes them suitable for processes requiring precise temperature control, such as drying and thermal treatments.
4. Large Surface Area: The fluidized state of the solid particles results in a large surface area available for contact with the fluidizing medium, facilitating rapid heat and mass transfer. This high surface area-to-volume ratio enhances the efficiency of processes carried out in fluidized beds.
5. Versatility: Fluidized beds are versatile and can be used for a wide range of applications across various industries, including chemical processing, pharmaceuticals, food and beverage production, and environmental engineering. They can accommodate different types of solid particles and fluidizing media, making them adaptable to diverse process requirements.