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The
vortex tube was invented quite by accident in 1928. George
Ranque, a French physics student, was experimenting with
a vortex-type pump he had developed when he noticed warm
air exhausting from one end, and cold air from the other.
Ranque soon forgot about his pump and started a small
firm to exploit the commercial potential for this strange
device that produced hot and cold air with no moving parts.
However, it soon failed and the vortex tube slipped into
obscurity until 1945 when Rudolph Hilsch, a German physicist,
published a widely read scientific paper on the device.
Much
earlier, the great nineteenth century physicist, James
Clerk Maxwell postulated that since heat involves the
movement of molecules, we might someday be able to get
hot and cold air from the same device with the help of
a "friendly little demon" who would sort out
and separate the hot and cold molecules of air.
Thus,
the vortex tube has been variously known as the "Ranque
Vortex Tube", the "Hilsch Tube",
the "Ranque-Hilsch Tube", and
"Maxwell’s Demon". By any
name, it has in recent years gained acceptance as a simple,
reliable and low cost answer to a wide variety of industrial
spot cooling problems.
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A
vortex tube uses compressed air as a power source,
has no moving parts, and produces hot air from one
end and cold air from the other. The volume and
temperature of these two airstreams are adjustable
with a valve built into the hot air exhaust. Temperatures
as low as -50°F (-46°C) and as high as +260°F (127°C)
are possible.
Theories
abound regarding the dynamics of a vortex tube.
Here is one widely accepted explanation of the phenomenon:
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Compressed
air is supplied to the vortex tube and passes through
nozzles that are tangent to an internal counterbore.
These nozzles set the air in a vortex motion. This
spinning stream of air turns 90° and passes down the
hot tube in the form of a spinning shell, similar
to a tornado. A valve at one end of the tube allows
some of the warmed air to escape. What does not escape,
heads back down the tube as a second vortex inside
the low-pressure area of the larger vortex. This inner
vortex loses heat and exhausts thru the other end
as cold air. |
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While
one airstream moves up the tube and the other down it,
both rotate in the same direction at the same angular
velocity. That is, a particle in the inner stream completes
one rotation in the same amount of time as a particle
in the outer stream. However, because of the principle
of conservation of angular momentum, the rotational speed
of the smaller vortex might be expected to increase. (The
conservation principle is demonstrated by spinning skaters
who can slow or speed up their spin by extending or drawing
in their arms.) But in the vortex tube, the speed of the
inner vortex remains the same. Angular momentum has been
lost from the inner vortex. The energy that is lost shows
up as heat in the outer vortex. Thus the outer vortex
becomes warm, and the inner vortex is cooled.
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