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G. RANQUE

Vortex Tube

Acoustic Vortex Heating / Cooling ( 100 * differential ) ... Construction, Analyses ofOperation, & Patents...

http://en.wikipedia.org/wiki/Vortex_tube

Vortex Tube

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 thatseparates a compressed gas into hot and cold streams. It has no moving parts.

Pressurized gas is injected tangentially into a swirl chamber and accelerates to a high rate ofrotation. Due to the conical nozzle at the end of the tube, only the outer shell of thecompressed gas is allowed to escape at that end. The remainder of the gas is forced to returnin an inner vortex of reduced diameter within the outer vortex.

There are different explanations for the effect and there is debate on which explanation isbest or correct.

What is usually agreed upon is that the air in the tube experiences mostly "solid bodyrotation", which simply means the rotation rate (angular velocity) of the inner gas is the sameas that of the outer gas. This is different from what most consider standard vortex behaviour--where inner fluid spins at a higher rate than outer fluid. The (mostly) solid body rotation isprobably due to the long time which each parcel of air remains in the vortex--allowing

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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 wanting to "rise" towardthe 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 thatof 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 istransferred as kinetic energy to the outer vortex, resulting in separated flows of hot and coldgas.[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 togrow cold.

When used to refrigerate, heat-sinking the whole vortex tube is helpful. Vortex tubes canalso be cascaded. The cold (or hot) output of one can be used to pre-cool (or pre-heat) theair supply to another vortex tube. Cascaded tubes can be used, for example, to producecryogenic temperatures.

History

The vortex tube was invented in 1933 by French physicist Georges J. Ranque. Germanphysicist Rudolf Hilsch improved the design and published a widely read paper in 1947 onthe device, which he called a Wirbelrohr (literally, whirl pipe).[2] Vortex tubes also seem towork with liquids to some extent.[3]

Efficiency

Vortex tubes have lower efficiency than traditional air conditioning equipment. They arecommonly used for inexpensive spot cooling, when compressed air is available. Commercialmodels are designed for industrial applications to produce a temperature drop of about 45 °C(80 °F).

Proposed applications

* Dave Williams, of dissigno, has proposed using vortex tubes to make ice in third-worldcountries. Although the technique is inefficient, Williams expressed hope that vortex tubescould 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 tubeenergy separation may be a method to recover waste pressure energy from high and lowpressure sources.[4]

References

1. ^ exair.com - Vortex tube theory -- http://www.exair.com/Cultures/en-US/Primary+Navigation/Products/Vortex+Tubes+and+Spot+Cooling/Vortex+Tubes/A+Phenomenon+of+Physics2. ^ *Rudolf Hilsch, The Use of the Expansion of Gases in A Centrifugal Field as CoolingProcess, The Review of Scientific Instruments, vol. 18(2), 108-1113, (1947). translation ofan article in Zeit. Naturwis. 1 (1946) 208. 3. ^ R.T. Balmer. Pressure-driven Ranque-Hilsch temperature separation in liquids. Trans.ASME, J. Fluids Engineering, 110:161–164, June 1988. 4. ^ Sachin U. Nimbalkar, Dr.M.R. Muller. Utilizing waste pressure in industrial systems.Energy: production, distribution and conservation, ASME-ATI 2006, Milan

General references

* G. Ranque, Expériences sur la Détente Giratoire avec Productions Simultanées d'unEchappement d'air Chaud et d'un Echappement d'air Froid, J. de Physique et Radium4(7)(1933) 112S. * H. C. Van Ness, Understanding Thermodynamics, New York: Dover, 1969, starting onpage 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 ScienceResearch 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.

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* 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: TemperatureSeparation Traced to Orderly Spinning Waves or 'Vortex Whistle', Paper AIAA-82-0952presented at the AIAA/ASME 3rd Joint Thermophysics Conference (June 1982) * Gao, Chengming. Experimental Study on the Ranque-Hilsch Vortex Tube. Eindhoven :Technische Universiteit Eindhoven. ISBN 90-386-2361-5.

See also

* Windhexe * Helikon vortex separation process

External links

* G. J. Ranque's U.S. Patent -- http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=%2Fnetahtml%2Fsearch-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN%2F1952281

* airtxinternational.com - AiRTX International, how vortex tubes work --http://www.airtxinternational.com/how_vortex_tubes_work.php

* Tim Cockerill's pages on the Ranque-Hilsch Vortex Tube, including his 1995 CambridgeUniversity thesis on the subject, and a mailing list. -- http://www.cockerill.net/rhvtmatl/

* How to Make Ice Out of Thin Air: Cool Heat Transfer, Daren Fonda, Sep. 4, 2005, TimeMagazine. (Requires membership) -- http://www.time.com/time/magazine/printout/0,8816,1101299,00.html

* Oberlin college physics demo --http://www.oberlin.edu/physics/catalog/demonstrations/thermo/vortextube.html

* itwvortec.com - Manufacturer of vortex tubes, information page --http://www.itwvortec.com/vortex_tubes.php

* The Hilsch Vortex Tube - Online copy of the Scientific American article by C. L. Stong --http://www.visi.com/~darus/hilsch/

* Home-brew vortex tube made from off-the-shelf parts - David Buchan's Ranque-Hilscheffect tube project using only off-the-shelf plumbing parts --http://www.pdbuchan.com/ranque-hilsch/ranque-hilsch.html

http://www.arizonavortex.com

Vortex tube uses and how do they work -- http://www.arizonavortex.com/vortex-tube

Vortex Tubes - Sub-Zero Spot Cooling from Compressed Air

Vortex Tubes are an effective, low cost solution to a wide variety of industrial spot coolingand process cooling needs. With no moving parts, a vortex tube spins compressed air toseparate the air into cold and hot air streams. While French physicist Georges Ranque iscredited with inventing the vortex tube in 1930, Vortec was the first company to develop andapply this phenomenon into practical and effective spot cooling solutions for industrial use.

Vortex Tube Applications:

Vortex Tubes have a very wide range of application for industrial spot cooling on machines,assembly lines and processes.

# Cool Machining Operations # Set solders and adhesives # Cool plastic injection molds # Dry ink on labels and bottles # Dehumidify gas operations # Cool heat seal operations # Thermal test sensors and choke units # Cool cutter blades # Temperature cycle parts

How a Vortex Tube Works

Fluid (air) that rotates around an axis (like a tornado) is called a vortex. A Vortex Tube

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creates cold air and hot air by forcing compressed air through a generation chamber whichspins the air centrifugally along the inner walls of the Tube at a high rate of speed (1,000,000RPM) toward the control valve. A percentage of the hot, high-speed air is permitted to exitat the control valve. The remainder of the (now slower) air stream is forced to counterflowup through the center of the high-speed air stream, giving up heat, through the center of thegeneration chamber finally exiting through the opposite end as extremely cold air. Vortextubes generate temperatures down to 100°F below inlet air temperature. A control valvelocated in the hot exhaust end can be used to adjust the temperature drop and rise for allVortex Tubes.

Vortex Tubes Features & Benefits

• Vortex Tubes use only compressed air for spot cooling- no electricity or refrigerants arerequired

• Vortex Tubes are maintenance free - Since Vortex Tubes have no moving parts there is nomaintence required

Vortex Tubes are Exceptionally reliable

Vortex Tubes are Compact and lightweight

Vortex Tube technologoy is Cycle repeatablity with ± 1 °

Vortex Tubes from Vortec drops inlet temperature by up to 100°F providing exceptional spotcooling

PDF Scans

1 -- Popular Science (May 1947 ); "Maxwell's Demon Comes to Life"

2 -- Compressed Air Mag. (August 1986 )

3 -- Cooling Vest ( Lab Safety Supply )

4 -- Roy McGee Jr : Refridgerating Engineering ; "Fluid Action in the Vortex Tube"

5 -- E. Eckert & J. Hartnett : "Investigation of the Energy Distribution in a HighVelocity Vortex Type Flow" ( Armour Research Symposium, May 1955 )

6 -- C. Pengelley : "Thermal Phenomena in a Vortex" ( Armour Research Symposium,May 1955 )

7 -- G. Scheper Jr : J. Amer. Soc. Refr. Engg. ( Oct. 1955 ); "The Vortex Tube --Internal Flow Data & a Heat Transfer Theory"

8 -- R. Hilsch : Review of Scientific Instruments 18 (2), Feb. 1947; "The Use of theExpansion of Gases in a Centrifugal Field as Cooling Process"

9 -- Greg Stone : Popular Science ( October 1976 ); "Vortex Tube Blows Hot andCold"

10 -- C. Fulton : J.A.S.R.E. ( May 1950 ) ; "Ranque's Tube"

11 -- Popular Science ( November 1967 ) ; "Homemade Maxwell's Demon Blows Hotand Cold"

12 -- Lab Safety Supply : "A Short Course on Vortex Tubes and Application Notes"

13 -- Leon Ranque : French Patent # 1066484 ; "Generatrice a Vapeur en CircuitFerme

US Patent # 1952281 "Method & Apparatus for Obtaining from a Fluid Under Pressure Two

Currents of Fluids at Different Temperatures" G. Ranque

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http://pubs.acs.org/doi/abs/10.1021/ie50570a035

The Ranque-Hilsch Vortex Tube

William A. Scheller, George M. Brown

Ind. Eng. Chem., 1957, 49 (6), pp 1013–1016 DOI: 10.1021/ie50570a035 Publication Date: June 1957

http://www.springerlink.com/content/u4146950k3050673/

Cryocoolers 12

Publisher Springer US ISBN 978-0-306-47714-0 (Print) 978-0-306-47919-9 (Online)

Study of a Vortex Tube by Analogy with a Heat Exchanger

Y. Cao2, Y.F. Qi3, E.C. Luo3, J.F Wu3, M.Q. Gong3 and G.M. Chen2 (2) Institute of Refrigeration and Cryogenic Engineering, Zhejiang University, Hangzhou,China, 310027 (3) Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing,China, 100080

Abstract -- Based on the models of Scheper, Lewins, and Bejan, a new model has beenestablished to study the influence of the cold mass flow fraction on the temperatureseparation effect in a vortex tube. The model is based on making an analogy between thevortex tube and a counterflow heat exchanger. The results show the model can accuratelyexplain the correlation of cold mass flow fraction to the temperature separation effect.

Newsgroups: sci.physics.fusion From: bernecky@starbase.nl.nuwc.navy.mil (W. Robert Bernecky) Subject: Wirbelrohr or vortex tube Sender: scott@zorch.SF-Bay.ORG (Scott Hazen Mueller) Date: Sat, 1 Jul 1995 23:11:02 GMT

The following may be relevant to the Potapov device.

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It contains excerpts from "And yet it moves...strange systems & subtle questions in physics,"by Mark P. Silverman, Cambridge University Press, 1993; Chpt 6 "The Wirbelrohr's roar".

[BILL B. NOTE: also see Scientific American, November 1958 for a Hilsch-tubeconstruction article in Stong's THE AMATEUR SCIENTIST]

"It was a Wirbelrohr, he explained; you blew into the stem, and out one end of the cross-tube flowed hot air, while cold air flowed out the other. I laughed; I was certain he wasteasing me. Although I had never heard of a Wirbelrohr, I recognised a Maxwell demonwhen it was described."

"...he machined in his basement workshop a working model which I received from himshortly afterwards. The exterior was more or less just as he had described it: two identicallong thin-walled tubes (the cross-bar of the T), were connected by cylindrical collarsscrewed into each end of a short section of pipe that formed the central chamber; a gas inletnozzle (the stem of the T), shorter than the other two tubes but otherwise of identicalconstruction, joined the midsection tangentially (Fig. 6.1). Externally, except for a throttlingvalve at the far end of one output tube to control air flow, the entire device manifestedbilateral symmetry with respect to a plane through the nozzle perpendicular to the cross-tubes.

"Only someone with the lung capacity of Hercules could actually blow into the stem.Instead, the nozzle was meant to be attached to a source of compressed air. Taking theWirbelrohr into my laboratory, I looked sceptically for a moment at its symmetrical shapebefore opening the valve by my work table that started the flow of room-temperaturecompressed air. Then, with frost forming on the outside surface of one tube, I yelped withpain and astonishment when, touching the other tube, I burned my fingers!"

"...With the few parts of the Wirbelrohr laid out on my table, I understood better thesignificance of the German name, Wirbelrohr, or vortex tube. The heart of the device is thecentral chamber with a spiral cavity and offset nozzle. Compressed gas entering thischamber streams around the walls of the cavity in a high-speed vortex. But what gives riseto spatially separated air currents at different temperatures? ...the placement in one cross-tube (the cold one) of a small-aperture diaphragm effectively blocked the efflux of gas alongthe walls of the tube, thereby forcing this part of the air flow to exit through the other armwhose cross-section was unconstrained.

|-----------| --------------| |------------------ | "COLD" PIPE "HOT" PIPE

| <--- diaphragm --------------| |------------------ |---| |---| / | | CENTRAL | | CHAMBER | | | | | <- INLET _____ / \

Fig 6 - Schematic of Wirbelrohr or / __ \ vortex tube. / / \ | / | Top View | | | \ | | / \ | | / | | / | |--- | | | | <- INLET | |

Room-temperature compressed air enters the inlet tube, spirals around the central chamber,and exits through the 'hot' pipe with unconstrained cross-section or through the 'cold' pipewhose aperture is restricted by a diaphragm.

[BILLB: the 'hot' tube should be partially blocked, with either a valve, or even better, anarrow ring-slot that lets air near the inner surface escape.]

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"The glimmer of a potential mechanism dawned on me. Had the in- coming air conservedangular momentum, the rotational frequency of air molecules nearest the axis of the centralchamber would be higher - as would also be the corresponding rotational kinetic energy -than peripheral layers of air. However, internal friction between gas layers comprising thevortex would tend to establish a constant angular velocity throughout the cross-section of thechamber. In other words, each layer of gas within the vortex would exert a tangential forceupon the next outer layer, thereby doing work upon it at the expense of its internal energy(while at the same time receiving kinetic energy from the preceding inner layer). Energywould consequently flow from the center radially outward to the walls generating a systemwith a low-pressure, cooled axial region and a high-pressure, heated circumferential region.Because of the diaphragm, the cooler axial air had to exit one tube (the cold side), whereas amixture of axial and peripheral air exited the other (the hot side).

"The presence of the throttling valve on the hot side now made sense. If the low pressure ofthe air nearest the axis of the tube fell below atmospheric pressure, the cold air would notexit at all...By throttling the flow, pressure within the central chamber was increasedsufficiently so that air could exit both tubes.

"...with some simplifying assumptions I was able to calculate the entropy change... Underwhat is termed adiabatic conditions - i.e. with no heat exchange with the environment - the2nd Law requires that the entropy change of the gas, alone, be >= zero. The resultingmathematical expression, augmented by the equation of state of an ideal diatomic gas andthe conservation of energy (1st Law) yields an inequality:

(x^f)[(1-fx)/(1-f)]^(1-f) >= (Pf/Pi)^(2/7)

where x= Tc/Ti Tc is temperature of cold air Ti is initial temperature Pf is the final pressure Pi is the initial pressure f is the fraction of gas directed thru the cold side

"By setting the expression for the entropy change equal to zero, I could calculate the lowesttemperature that the cold tube should be able to reach if the gas flow were an idealreversible process. The result was astonishing. With an input pressure of 10 atmospheres andthe throttling set for a fraction f= 0.3, compressed air at room temperature (20 C) could inprinciple be cooled to about -258 C, a mere 15 degrees above absolute zero! (Thecorresponding temperature of the hot side would have been 80 C.)

"...The first experimental demonstation of a vortex tube seems to have been reported in 1933by a French engineer, Georges Ranque [1]. by German physicist Rudolph Hilsch came to theattention of American chemist R.M. Milton... In Hilsch's hands, proper selection of the airfraction f (~ .33) and an input pressure of a few atmospheres gave rise to an amazing outputof 200 C at the hot end and -50 C at the cold end[2]. Hilsch, who was the one to coin theterm Wirbelrohr, used the tube in place of an ammonia pre-cooling apparatus in a machineto liquify air.

"...Milton was not satisfied with the interpretation of Hilsch and Ranque that frictional lossof kinetic energy produced the radial temperature distribution...."

M Kurosaka, et al [3,4], in 1982, proposed a far different mechanism, supported byexperiment.

"With a loud roar air rushes turbulently thru the Wirbelrohr, just as it does thru a jet engineor a vacuum cleaner. Buried within that roar, however, is a pure tone, a "vortex whistle" as ithas been called...the vortex whistle can be produced by tangential introduction and swirlingof gas in a stationary tube. It is this pure tone that is purportedly responsible for thespectacular separation of temperature in a vortex tube.

"The Ranque-Hilsch effect is a steady-state phenomenon - i.e. an effect that survivesaveraging over time. How can a high-pitch whistle - a sound that, depending on air velocityand cavity geometry, can be on the order of a few kilohertz - influence the steady componentof flow? The answer...was by 'acoustic streaming'. As a result of a small nonlinearconvection term in the fluid equation of motion, an acoustic wave can act back upon thesteady flow and modify its properties substantially. In the absence of unsteady disturbances,the air flows in a 'free' vortex around the axis of the tube; the speed of the air is close to zeroat the center (like a hurricane), increases to a maximum at mid-radius, and drops to a smallvalue near the walls. Acoustic streaming, however, deforms the free vortex into a 'forced'vortex where the air speed increases linearly from the center to the periphery. Acousticstreaming and the production of a forece vortex, rather than mere static centrifugation,engender the Ranque-Hilsch effect.

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"The experimental test could not be more direct. Remove the whistle, and only the whistle,and see whether the radial temperature distribution remains. To do this [Kurosaka] monitoredthe entireroar with a microphone and ...decomposed it into frequencies of which the discretecomponent of the lowest frequency and largestamplitude was identified as the vortex whistle.Next, he enclosed the Wirbelrohr inside a tunable acoustic suppressor: a cylindrical sectionof Teflon with radially drilled holes serving as acoustic cavities distributed uniformly aroundthe circumference. Inside each hole was a small tuning rod that could be inserted until ittouched the outer shell of the Wirbelrohr to close off the cavity, or withdrawn incrementallyto make the cavity resonant at the specified frequency to be suppressed.

"To simplify the experimental test, he sealed off one output of the vortex tube and monitoredwith thermocouples the temperature difference between the center and periphery. In theabsence of the suppressor, an increase in pressure produced, as I had noticed whenexperimenting with my own vortex tube, a louder roar and greater temperature difference.When, however, the acoustic cavity was adjusted to suppress only the frequency of thevortex whistle (leaving unaffected the rest of the turbulent noise), the temperature differenceplunged precipitously at the instant the corresponding input air pressure was reached. In onesuch trial, the centerline temperature jumped 33 C, from -50 C to -17 C. With furtherincrease in pressure, the frequency of the whistle rose, and as it exceeded the narrow band ofthe acoustic suppressor, the temperature difference increased again.

"Additional evidence came from a striking transformation in the nature of the flow...Beforethe vortex whistle was suppressed, the exhaust air swirled rapidly near and outside the tubeperiphery in the manner expected for a forced vortex. Upon supprssion, however, the forcedvortex was also abruptly suppressed; now quiescent at the periphery, the air rushed out closeto the centerline."

"For all I know, the case of the mysterious Wirbelrohr is largely closed although, sciencebeing what it is, future version of that device may yet hold some suprises in store. I havesometimes wondered, for example, what would result from supplying a vortex tube, not withroom-temperature air, but with a quantum fluid, like liquid helium, free of viscosity andfriction.

The exorcism of the demon in the Wirbelrohr will not, I suspect, dampen one bit the ardourof those whose passion it is to challenge the 2nd Law. Despite the time and effort that hasbeen frittered away in the past, others will undoubtedly try again. On the whole suchschemes are bound to fail, but every so often, as in the case of Maxwell's own whimsicalcreation, this failure has its positive side: when, from the clash between human ingenuityand the laws of nature, there emerge sounder knowledge and deeper understanding."

[1] G. Ranque, "Experiences sur la Detente Giratore avec Productions Simultanees d'unEchappement d'air Chaud et d'un Echappement d'air Froid", J. de Physique et Radium4(7)(1933) 112 S.

[2] R. Hilsch, "The Use of the Expansion of Gases in a Centrifugal Field as CoolingProcess", Rev. Sci. Instrum. 18(2) (1947) 108-1113.

[3] M. Kurosaka, "Acoustic Streaming in Swirling Flow and the Ranque-Hilsch (VortexTube) Effect", J. Fluid Mech. 124(1982)139.

[4] M. Kurosaka, J.Q. Chu, & J.R. Goodman, "Ranque-Hilsch Effect Revisited: TemperatureSeparation Traced to Orderly Spinning Waves or Vortex Whistle", conference of Am Inst. ofAero & Astro 1982.

[OTHERS]

C. L. Stong, The "Hilsch" Vortex Tube, The Amateur Scientist, Scientific American, 514-519.

J. J. Van Deemter, On the Theory of the Ranque-Hilsch Cooling Effect, Applied ScienceResearch 3, 174-196.

C.L. Stong : "The Scientific American Book of Projects for the Amateur Scientist," pp.514-520 ' Simon and Schuser, NY, 1960. C.L. Stong : Scientific American, November 1958, p. 45. Illustrations by Roger Hayward

THE "HILSCH" VORTEX TUBE

With nothing more than a few pieces of plumbing and a source of compressed air, you canbuild a remarkably simple device for attaining moderately low temperatures. It separates

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high-energy molecules from those of low energy. George O. Smith, an engineer of Rumson,N. I., discusses its theory and construction

The 19th century British physicist James Clerk Maxwell made many deep contributions tophysics, and among the most significant was his law of random distribution. Considering. thecase of a closed box containing a gas, Maxwell started off by saying that the temperature ofthe gas was due to the motion of the individual gas molecules within the box. But since thebox was standing still, it stood to reason that the summation of the velocity and direction ofthe individual gas molecules must come to zero.

In essence Maxwell's law of random distribution says that for every gas molecule headedeast at 20 miles per hour, there must be another headed west at the same speed. Furthermore,if the heat of the gas indicates that the average velocity of the molecules is 20 miles per hour,the number of molecules moving slower than this speed must be equaled by the number ofmolecules moving faster.

After a serious analysis of the consequences of his law, Maxwell permitted himself a touchof humor. He suggested that there was a statistical probability that; at some time in thefuture, all the molecules in a box of gas or a glass of hot water might be moving in the samedirection. This would cause the water to rise out of the glass. Next Maxwell suggested that asystem of drawing both hot and cold water out of a single pipe might be devised if we couldcapture a small demon and train him to open and close a tiny valve. The demon would openthe valve only when a fast molecule approached it, and close the valve against slowmolecules. The water coming out of the valve would thus be hot. To produce a stream ofcold water the demon would open the valve only for slow molecules.

Maxwell's demon would circumvent the law of thermodynamics which says in essence:"You can't get something for nothing." That is to say, one cannot separate cold water fromhot without doing work. Thus when physicists heard that the Germans had developed adevice which could achieve low temperatures by utilizing Maxwell's demon, they wereintrigued, though obviously skeptical. One physicist investigated the matter at first hand forthe U. S. Navy. He discovered that the device was most ingenious, though not quite asmiraculous as had been rumored.

234

It consists of a T-shaped assembly of pipe joined by a novel fitting, as depicted in Figure234. when compressed air is admitted to the "leg" of the T, hot air comes out of one arm ofthe T and cold air out of the other arm! Obviously, however, work must be done to compress

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the air.

The origin of the device is obscure. The principle is said to have been discovered by aFrenchman who left some early experimental models in the path of the German Army whenFrance was occupied. These were turned over to a German physicist named Rudolf Hilsch,who was working on low temperature refrigerating devices for the German war effort. Hilschmade some improvements on the Frenchman's design, but found that it was no more efficientthan conventional methods of refrigeration in achieving fairly low temperatures.Subsequently the device became known as the Hilsch tube.

235

The Hilsch tube may be constructed from a pair of modified nuts and associated parts asshown in Figure 235. The horizontal arm of the T-shaped fitting contains a speciallymachined piece, the outside of which fits inside the arm. The inside of the piece, however,has a cross section which is spiral with respect to the outside. In the "step" of the spiral is asmall opening which is connected to the leg of the T Thus air admitted to the leg comes outof the opening and spins around the one-turn spiral. The "hot" pipe is about 14 inches longand has an inside diameter of half an inch. The far end of this pipe is fitted with a stopcock

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which can be used to control the pressure in the system [see Fig. 236].

236

The "cold" pipe is about four inches long and also has an inside diameter of half an inch.The end of the pipe which butts up against the spiral piece is fitted with a washer, the centralhole of which is about a quarter of an inch in diameter. Washers with larger or smaller holescan also be inserted to adjust the system.

Three factors determine the performance of the Hilsch tube; the setting of the stopcock, thepressure at which air is admitted to the nozzle, and the size of the hole in the washer. Foreach value of air pressure and washer opening there is a setting of the stopcock which resultsin a maximum difference in the temperature of the hot and cold pipes [see Fig. 237].

237

When the device is properly adjusted, the hot pipe will deliver air at about 100 degreesFahrenheit and the cold pipe air at about -70 degrees (a temperature substantially below thefreezing point of mercury and approaching that of "dry ice"). When the tube is adjusted formaximum temperature on the hot side, air is delivered at about 350 degrees F. It must bementioned, however, that few amateurs have succeeded in achieving these performanceextremes. Most report minimums on the order of -10 degrees and maximums of about + 140on the first try. Despite its impressive performance, the efficiency of the Hilsch tube leavesmuch to be desired. Indeed, there is still disagreement as to how it works. According to oneexplanation, the compressed air shoots around the spiral and forms a high-velocity vortex ofair. Molecules of air at the outside of the vortex are slowed by friction with the wall of thespiral. Because these slow-moving molecules are subject to the rules of centrifugal force,they tend to fall toward the center of the vortex. The fast-moving molecules just inside theouter layer of the vortex transfer some of their energy to this layer by bombarding some of

19.03.11 15.24G . Ranque -- Vortex Tube -- Acoustic heating / cooling

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its slow-moving molecules and speeding them up. The net result of this process is theaccumulation of slow-moving, low-energy molecules in the center of the whirling mass, andof high-energy, fast-moving molecules around the outside. In the thermodynamics of gasesthe terms "high energy" and "high velocity" mean "high temperature." So the vortex consistsof a core of cold air surrounded by a rim of hot air.

The difference between the temperature of the core and that of the rim is increased by asecondary effect which takes advantage of the fact that the temperature of a given quantity ofgas at a given level of thermal energy is higher when the gas is confined in a small spacethan in a large one; accordingly when gas is allowed to expand, its temperature drops. In thecase of the Hilsch tube the action of centrifugal force compresses the hot rim of gas into acompact mass which can escape only by flowing along the inner wall of the "hot" pipe in acompressed state, because its flow into the cold tube is blocked by the rim of the washer.

The amount of the compression is determined by the adjustment of the stopcock at the end ofthe hot pipe. In contrast, the relatively cold inner core of the vortex, which is alsoconsiderably above atmospheric pressure, flows through the hole in the washer and drops tostill lower temperature as it expands to atmospheric pressure obtaining inside the cold pipe.

Apparently the inefficiency of the Hilsch tube as a refrigerating device has barred itscommercial application. Nonetheless amateurs who would like to have a means of attainingrelatively low temperatures, and who do not have access to a supply of dry ice, may find thetube useful. when properly made it will deliver a blast of air 20 times colder than air whichhas been chilled by permitting it simply to expand through a Venturi tube from a high-pressure source. Thus the Hilsch tube could be used to quick- freeze tissues for microscopy,or to chill photomultiplier tubes. But quite apart from the tube's potential application, whatcould be more fun than to trap Maxwell's demon and make him explain in detail how hemanages to blow hot and cold at the same time?

Incidentally, this is not a project for the person who goes in for commercially madeapparatus. So far as I can discover Hilsch tubes are not to be found on the market. You mustmake your own. Nor is it a project for the experimenter who makes a speciality of buildingapparatus from detailed specifications and drawings. The dimensions shown in theaccompanying figures are only approximate. Certainly they are not optimum values. But ifyou enjoy exploration, the device poses many questions. What would be the effect, forexample, of substituting a divergent nozzle for the straight one used by Hilsch? Why notcreate the vortex by impeller vanes, such as those employed in the stator of turbines? Woulda spiral chamber in the shape of a torus improve the efficiency? What ratio should thediameter of the pipes bear to the vortex chamber and to each other? Why not make the spiralof plastic, or even plastic wood? One can also imagine a spiral bent of a strip of brass andsoldered into a conventional pipe coupling. Doubtless other and far more clever alternativeswill occur to the dyed-in-the-wool tinkerer.

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