The
vortex tube, also known as the
Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed
gasGas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
into hot and cold streams. It has no
moving partsThe moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....
.
Pressurized gas is injected tangentially into a
swirl chamber and accelerated to a high rate of
rotationA rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
. Due to the
conicalA cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
nozzleA nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
at the end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex.
There are different explanations for the effect and there is debate on which explanation is best or correct.
What is usually agreed upon is that the air in the tube experiences mostly "
solid bodyA solid-body instrument is a string instrument such as a guitar, bass or violin built without its normal sound box and relying on an electric pickup system to directly receive the vibrations of the strings....
rotation", which simply means the rotation rate (
angular velocityIn physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...
) of the inner gas is the same as that of the outer gas. This is different from what most consider standard
vortexA vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...
behavior — where inner
fluidIn physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
spins at a higher rate than outer fluid. The (mostly) solid body rotation is probably due to the long time which each parcel of air remains in the vortex — allowing friction between the inner parcels and outer parcels to have a notable effect.
It is also usually agreed upon that there is a slight effect of hot air tending to "rise" toward the center, but this effect is negligible — especially if
turbulenceIn fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
is kept to a minimum.
One simple explanation is that the outer air is under higher pressure than the inner air (because of
centrifugal forceCentrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
). Therefore the
temperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
of the outer air is higher than that of the inner air.
Another explanation is that as both vortices rotate at the same angular velocity and direction, the inner vortex has lost
angular momentumIn physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
. The decrease of angular momentum is transferred as
kinetic energyThe kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
to the outer vortex, resulting in separated flows of hot and cold gas.
This is somewhat analogous to a Peltier effect device, which uses electrical pressure (
voltageVoltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
) to move heat to one side of a dissimilar metal junction, causing the other side to grow cold.
When used to refrigerate, heat-sinking the whole vortex tube is helpful.
History
The vortex tube was invented in 1933 by French physicist Georges J. Ranque. German physicist Rudolf Hilsch improved the design and published a widely read paper in 1947 on the device, which he called a
Wirbelrohr (literally, whirl pipe). The vortex tube was used to separate gas mixtures, oxygen and nitrogen, carbon dioxide and helium, carbon dioxide and air in 1967 by Linderstrom-Lang.
Vortex tubes also seem to work with liquids to some extent. In 1988 R.T.Balmer applied liquid water as the working medium. It was found that when the inlet pressure is high, for instance 20-50 bar, the heat energy separation process exists in incompressible (liquids) vortex flow as well.
Efficiency
Vortex tubes have lower efficiency than traditional
air conditioningAn air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
equipment. They are commonly used for inexpensive spot cooling, when compressed air is available. Commercial models are designed for industrial applications to produce a temperature drop of about 45 °C (80 °F). With no moving parts, no electricity, and no Freon, a vortex tube can produce refrigeration up to 6000 BTU using only filtered compressed air at 100 PSI. A control valve in the hot air exhaust adjusts temperatures, flows and refrigeration over a wide range.
Proposed applications
- Dave Williams, of dissigno, has proposed using vortex tubes to make ice in third-world countries. Although the technique is inefficient, Williams expressed hope that vortex tubes could yield helpful results in areas where using electricity to create ice is not an option.
- There are industrial applications that result in unused pressurized gases. Using vortex tube energy separation may be a method to recover waste pressure energy from high and low pressure sources.
Further reading
- G. Ranque, Expériences sur la Détente Giratoire avec Productions Simultanées d'un Echappement d'air Chaud et d'un Echappement d'air Froid, J. de Physique et Radium 4(7)(1933) 112S.
- H. C. Van Ness, Understanding Thermodynamics, New York: Dover, 1969, starting on page 53. A discussion of the vortex tube in terms of conventional thermodynamics.
- Mark P. Silverman, And Yet it Moves: Strange Systems and Subtle Questions in Physics, Cambridge, 1993, Chapter 6
- C. L. Stong, The Amateur Scientist, London: Heinemann Educational Books Ltd, 1962, Chapter IX, Section 4, The "Hilsch" Vortex Tube, p514-519.
- J. J. Van Deemter, On the Theory of the Ranque-Hilsch Cooling Effect, Applied Science Research 3, 174-196.
- Saidi, M.H. and Valipour, M.S., "Experimental Modeling of Vortex Tube Refrigerator", J. of Applied Thermal Engineering, Vol.23, pp. 1971-1980, 2003.
- M. Kurosaka, Acoustic Streaming in Swirling Flow and the Ranque-Hilsch (vortex-tube) Effect, Journal of Fluid Mechanics, 1982, 124:139-172
- M. Kurosaka, J.Q. Chu, J.R. Goodman, Ranque-Hilsch Effect Revisited: Temperature Separation Traced to Orderly Spinning Waves or 'Vortex Whistle', Paper AIAA-82-0952 presented at the AIAA/ASME 3rd Joint Thermophysics Conference (June 1982)
- R. Ricci, A. Secchiaroli, V. D’Alessandro, S. Montelpare. Numerical analysis of compressible turbulent helical flow in a Ranque-Hilsch vortex tube. Computational Methods and Experimental Measurement XIV, pp. 353-364, Ed. C. Brebbia, C.M. Carlomagno, ISBN 978-1-84564-187-0.
- A. Secchiaroli, R. Ricci, S. Montelpare, V. D’Alessandro. Fluid Dynamics Analysis of a Ranque-Hilsch Vortex-Tube. Il Nuovo Cimento C, vol.32, 2009, ISSN 1124-1896.
- A. Secchiaroli, R. Ricci, S. Montelpare, V. D’Alessandro. Numerical simulation of turbulent flow in a Ranque-Hilsch vortex-tube. Int. J. of Heat and Mass Transfer, Vol. 52, Issues 23-24, November 2009, pp. 5496-5511, ISSN 0017-9310.
External links