Fluidization

In the process where a granular material is converted form a static solid-like state to a dynamic fluid-like state is what known as Fluidization. When this process happens a fluid is passed up via granular material. The gas flow is sent through the bottom of a bed of solid particles and will move towards through the bed via the empty spaces between the particles. Aerodynamic drag on each particle is also low during low gas velocities and the bed stay behind in a fixed state. Once the velocity increases the aerodynamic drag forces will begin to thwart the gravitational forces sourcing the bed to extend in volume as the particles pass from one another.

Gas velocity and causing particles

In addition to raising the velocity, it will attain a critical value at which the upward drag forces will precisely identical downward gravitational forces, sourcing the particles to become suspended within the fluid. At this serious value, the bed is to be fluidized and will show fluidic behavior. In addition raising gas velocity, the bulk density of the bed will continue to reduce, and its fluidization becomes more aggressive, until the particles no longer create a bed and are conveyed upwards by the gas flow.

The fluidic behavior

When fluidized, a bed of solid particles will act as a fluid such as liquid or gas. For instance like water in a bucket for which the bed will conform to the volume of the chamber, its surface remaining vertical to gravity and such objects with a lower density will float on its surface, bobbing up and down if pushed downwards while objects with a higher density drop to the bottom of the bed. The fluidic behavior permits the particles to be transported like a fluid, channeled through pipes not needing mechanical transport.

An example to understand fluidization

An ordinary routine life example of a gas-solid fluidization bed would be a hot air popcorn popper. The popcorn kernels, all being fairly consistent in size and shape, are suspended in the hot-air rising from the bottom chamber. This is because of the intense mixing of the particles, akin to that of a boiling liquid, this permits for a consistent temperature of the kernels all through the chamber, diminish the amount of burnt popcorn. After popping, the now larger popcorn particles meet increased aerodynamic drag which pushes them out of the chamber and into a bowl. And this particular process is also vital in the formation of a sand volcano and fluid escape structures in sediments and sedimentary rocks.

Questions:

• What is fluidization?
• State the significance of fluidization.