Techne IFB-131, Operator'S Manual

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I F B - 1 3 1 O P E R A T O R ’ S M A N U A L
PAGE 9
GENERAL DESCRIPTION
The fluidised bath employs the principle of fluidisation of a mass of finely divided
inert particles by means of an upward flow of gas. A state of fluidisation is achieved when the
individual particles become microscopically separated from each other by the moving gas. This
“fluidised bed” of particles has unusual properties which differ markedly from either those of the
gas or of the solid particles. Instead, the fluidised bed behaves remarkably like a liquid,
exhibiting characteristics which generally attribute to a liquid state. For example, the fluidised
bed can be agitated and bubbled; it always seeks a common level; materials of less density will
float while those with densities greater than the equivalent fluidised bed density will sink; and,
most important, the heat transfer characteristics between the fluidised bed and a solid interface
can have an efficiency approaching that of an agitated liquid.
In addition, the fluidised solid phase has a most unusual physical behaviour, in that
its basic characteristics change only slightly over very large temperature ranges; it has no
melting point and no boiling point. The lowest temperature available is the liquefaction point of
the gas used for fluidisation, while the high temperature level is usable temperature of the inert
solid. Various metal oxides with allowable temperatures of over 1700°C are readily available.
The metal oxide beds commonly used, (Eg aluminium oxide) are non-flammable, non-explosive
and non-toxic.
The most commonly used fluidised gas is ordinary compressed air obtained from a
blower or compressor. For situations where a non - oxidising atmosphere is required, nitrogen
can be utilised and if a reducing atmosphere is required, cracked gas can be employed with a
silicon carbide bed.
The unique characteristics of gas fluidised particles is the relatively high rate of heat
transfer which yields highly isothermal conditions, as well as excellent heat transfer to solid
surfaces. This characteristic is due to the turbulent motion and rapid circulation rate of the solid
particles in conjunction with the extremely high solid gas interface area. Therefore, despite the
fact that gas solid interfaces normally yield low heat transfer coefficients and the solids normally
have low thermal conductivities, the overall heat transfer characteristics of fluidised particles
approach those of a liquid.
The combination of excellent heat transfer characteristics and high heat capacity
are ideal for attaining rapid stabilisation at an isothermal condition.
Techne industrial fluidised baths use aluminium oxide as the fluidising medium.
They have been designed to remove plastic residue from extruder and moulding machine tools,
paint build up from paint fixtures, and carry out various heat treatment processes.
The fluidised bed is housed in a circular stainless steel container which has an
effluent gas extract duct and fluidised medium drain chute. The container is surrounded by
electrical heating elements which are enclosed within thermal insulation. The inner assembly is
housed in a square outer case which also supports the electrical and pneumatic control
console.
The following control options are available:
A manual control system which consists of a temperature controller, an independent
over-temperature cut-out device, a fluidising air pressure interlock, and a manually adjusting
fluidising air control valve. Supplied as standard with this, and all other options, is an air
pressure regulator and filter assembly.