IntrODuCtIOn
Read the whole of this book before commencing work with the unit.
The Techne FB-08C employs the principle of fluidisation of a mass of finely divided particles to provide a
safe, essentially isothermal environment with a high rate of heat transfer.
To achieve a state of fluidisation, a gas stream is forced to pass vertically through the bed of fine powder;
chromatographic alumina (a specially refined grade of aluminium oxide) is the fluidising medium used in
the FB-08C. At, and above, a certain critical value of flow rate the particles become separated from each
other and the whole mass behaves like a liquid. In this state the powder will flow and move as though
it were a liquid; low density objects will float on it, while more dense ones will sink; more importantly,
though, the individual alumina particles will circulate within the bath giving an essentially uniform
temperature distribution throughout the working volume of the bath, and a high degree of thermal
coupling between the heat source and load.
In addition, the mass of fluidised powder changes its basic characteristics very little over a wide
temperature range, has no freezing point and no practical boiling point and therefore by suitable choice
of fluidising media, the principle of fluidisation can be used to temperatures over 1700°C and below
-120°C.
The most commonly used fluidising gas is compressed air, it is important that it should be clean, dry, free
from oil and at a constant pressure. Techne can supply an additional filter/regulator assembly for
compressed air which does not comply with the above requirement. Techne are alternatively able to offer
a suitable free standing air compressor complete with the necessary filtration system for installations
where a compressed air supply is not available. Any other gas could be used for special applications
provided appropriate precautions are taken. The FB-08C specification applies only when dry compressed
air is used.
applICatIOn
The characteristics of the FB-08C in terms of thermal uniformity and heat transfer make it a useful tool in the
calibration and testing of a very wide range of temperature sensors; however, the unit is applicable to many
other processes, such as thermal testing of sensitive components - eg semiconductor devices, wire products,
delicate transducers - and can be used as a constant temperature environment for chemical reactions.
Because the fluidised bed is composed of a fine dry powder, it does not display the surface tension effects of
liquid baths, and does not wet any objects immersed in it; the basic electrical insulating property of the alumina
used in the FB-08C is not affected by fluidisation, making it possible to conduct electrical measurements on
immersed objects such as assembled printed circuit boards.
This special version of the FB-08 is fitted with a temperature controller which has an RS232 serial interface which
enables the operating temperature to be set and monitored by a remote computer.
An automatic fluidising air control system is fitted to enable unsupervised operation of the system because it is
essential that the fluidising air rate is altered as the temperature of the fluidised bed changes. To enable 'dead
bed' calibration techniques to be used, a facility is supplied which isolates the heater elements and collapses the
fluidised bed. This is initiated by an alarm in the temperature controller.
Avoid sitting the FB-08C in a laboratory environment which contains instruments that are sensitive to dust.
Although the fluidised bath has its own dust extraction system, a small amount of fine dust may still be emitted
during operation.
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