Editing Fluidization (section)

{{Short description|Conversion of a granular material from a solid-like to liquid-like state}}
{{more footnotes needed|date=March 2014}}

[[File:Fluidized Bed Reactor Graphic.svg|thumb|300px|Schematic drawing of a fluidized bed reactor]]

'''Fluidization''' (or '''fluidisation''') is a process similar to [[liquefaction]] whereby a [[granular material]] is converted from a static [[solid]]-like state to a dynamic [[fluid]]-like state. This process occurs when a fluid ([[liquid]] or [[gas]]) is passed up through the granular material.

When a gas flow is introduced through the bottom of a bed of solid particles, it will move upwards through the bed via the empty spaces between the particles.  At low gas velocities, aerodynamic [[Drag (physics)|drag]] on each particle is also low, and thus the bed remains in a fixed state.  Increasing the velocity, the aerodynamic drag forces will begin to counteract the gravitational forces, causing the bed to expand in volume as the particles move away from each other.  Further increasing the velocity, it will reach a critical value at which the upward drag forces will exactly equal the downward gravitational forces, causing the particles to become suspended within the fluid.  At this critical value, the bed is said to be fluidized and will exhibit fluidic behavior.  By further increasing gas velocity, the bulk density of the bed will continue to decrease, and its fluidization becomes more intense until the particles no longer form a bed and are "conveyed" upwards by the gas flow. 
 
When fluidized, a bed of solid particles will behave as a fluid, like a liquid or gas.  Like [[water]] in a [[bucket]]: the bed will conform to the volume of the chamber, its surface remaining perpendicular to [[gravity]]; objects with a lower density than the bed density will float on its surface, bobbing up and down if pushed downwards, while objects with a higher density sink to the bottom of the bed.  The fluidic behavior allows the particles to be transported like a fluid, channeled through [[water pipe|pipe]]s, not requiring mechanical transport (e.g. [[conveyor belt]]).

A simplified every-day-life example of a gas-solid [[fluidized bed]] would be a hot-air [[popcorn maker|popcorn popper]].  The [[popcorn|popcorn kernel]]s, all being fairly uniform in size and shape, are suspended in the hot air rising from the bottom chamber. Because of the intense mixing of the particles, akin to that of a boiling liquid, this allows for a uniform temperature of the kernels throughout the chamber, minimizing the amount of burnt popcorn.  After popping, the now larger popcorn particles encounter increased aerodynamic drag which pushes them out of the chamber and into a bowl.

The process is also key in the formation of a [[sand volcano]] and fluid escape structures in [[sediment]]s and [[sedimentary rock]]s.