How do fluidised baths work

About Fluidized baths

What is a Fluidized Bath and how do they work?
See this video of a fluidized bath in operation (4.2Mb MPEG)

Techne® Fluidized Baths, for laboratory, industrial, process, quality control and instrument shop use, provide rapid heat transfer and precise temperature control, enabling you to calibrate and maintain temperature sensitive instruments and devices efficiently, economically, and safely. Techne® Fluidized Baths offer outstanding advantages of being dry, inert, and non-corrosive as well as being non-abrasive to anything placed in them.
Aluminum oxide (AL₂O₃)particles serve as the heat transfer medium and have no affect on shape or size of immersed objects. This medium consists of a loosely-packed mass of solid particles which are agitated by a vertical flow of gas. In the fluidized state, the aluminum oxide particles become mobile and the bath as a whole displays many of the properties of a liquid. Visually when fluidized the aluminum oxide looks like liquid boiling vigorously or molten lava bubbling. The bed of levitated particles presents a very large surface area through which heat is transferred to immersed objects. Typical heat transfer rates are 60 to 120 Btu-hr-sq ft-°F. Below you can see the cutaway diagram of a fluidized bath.
Fluidized Aluminum oxide has no melting or boiling point, thus solidification which occurs in cooling salt baths and fumes from hot oil baths are eliminated. Heat transfer characteristics between the fluidized bed and the solid interface are similar to those of an agitated liquid - the key to fluidized bath calibration efficiency.

Typical Applications for Fluidized baths -
When a wide temperature range, good stability and uniformity and large working area is required, there are many potential applications for fluidized baths. These include: temperature sensor calibration, heat treatment, chemical processes, quench bath, distillation reactions, tempering and annealing of metals, stressing and forming of certain metals, burning off paints, films and oils, burning off of residual plastic from parts and molds used in plastics manufacturing including injection and blow molding. And because the aluminum oxide has a high electrical insulation value live electrical circuits and PCB's can be put into the baths for thermal analysis with a much more efficient recovery time than ovens.

Fluidised bath cutaway
Cutaway of Fluidized bath