Vortex tube

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For the term 'vortex-tube' used in fluid dynamics please see: vorticity
Separation of a compressed gas into a hot stream and a cold stream

The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. It has no moving parts.

Pressurized gas is injected tangentially into a swirl chamber and accelerated to a high rate of rotation. Due to the conical nozzle 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 body rotation", which simply means the rotation rate (angular velocity) of the inner gas is the same as that of the outer gas. This is different from what most consider standard vortex behavior — where inner fluid 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 turbulence is kept to a minimum.

One simple explanation is that the outer air is under higher pressure than the inner air (because of centrifugal force). Therefore the temperature 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 momentum. The decrease of angular momentum is transferred as kinetic energy to the outer vortex, resulting in separated flows of hot and cold gas.[1]

This is somewhat analogous to a Peltier effect device, which uses electrical pressure (voltage) 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.

Contents

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).[2] 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.[3] [4] Vortex tubes also seem to work with liquids to some extent. [5]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 conditioning equipment. They are commonly used for inexpensive spot cooling, when compressed air is available.

Applications

Current applications

Commercial vortex tubes 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 6,000 BTU (6,300 kJ) using only filtered compressed air at 100 PSI (689 kPa). A control valve in the hot air exhaust adjusts temperatures, flows and refrigeration over a wide range.[6]

Vortex tubes are used for cooling of cutting tools (lathes and mills, both manually-operated and CNC machines) during machining. The vortex tube is well-matched to this application: machine shops generally already use compressed air, and a fast jet of cold air provides both cooling and removal of the "chips" produced by the tool. This completely elimininates or drastically reduces the need for liquid coolant, which is messy, expensive, and environmentally hazardous.

Proposed applications

See also

References

  1. ^ exair.com - Vortex tube theory
  2. ^ *Rudolf Hilsch, The Use of the Expansion of Gases in A Centrifugal Field as Cooling Process, The Review of Scientific Instruments, vol. 18(2), 108-1113, (1947). translation of an article in Zeit. Naturwis. 1 (1946) 208.
  3. ^ Chengming Gao, Experimental Study on the Ranque-Hilsch Vortex Tube, (2005) page 2
  4. ^ Vortex tubes are constructed of stainless steel and use a generator and valve made of brass and sealed with viton o-rings to allow their use in the widest range of environments.
  5. ^ R.T. Balmer. Pressure-driven Ranque-Hilsch temperature separation in liquids. Trans. ASME, J. Fluids Engineering, 110:161–164, June 1988.
  6. ^ Newman Tools Inc. http://www.newmantools.com/vortex.htm
  7. ^ Sachin U. Nimbalkar, Dr.M.R. Muller. Utilizing waste pressure in industrial systems. Energy: production, distribution and conservation, ASME-ATI 2006, Milan

Further reading

External links