Sciencemadness Discussion Board

Ranque-Hilsch vortex tubes.

Tacho - 4-12-2005 at 10:00

I discovered the Ranque-Hilsch vortex tubes last tuesday afternoon and it has blown my mind.

For those 99,99% who have never heard of it: with some pipes, fittings and compressed air you can obtain low temperatures! Check:
http://www.visi.com/~darus/hilsch/

The full article is in a book mentioned here. Wonderfull stuff BTW, thanks Poverone.

Another link:
http://www.exair.com/vortextube/vt_page.htm

I have downloaded a few papers on the subject and made a couple of prototypes. I even thought of using my vacuum pump to drive one, someone did that and the paper is attached here (thanks andresderis).
Anyone would like to exchange ideas?

BromicAcid - 4-12-2005 at 15:14

So, let me get this straight, you somehow put a demon inside of the tube and it separates the hot from the cold thereby making the hot hotter and the cold colder? ;)

-70C is incredible, although is specifies this would take a well tuned apparatus -10 is pretty good too. Very very interesting setup, looking foreward to seeing someone do something with one and give some positive information.

Twospoons - 4-12-2005 at 15:24

I looked at these several years ago and thought maybe one could be used in the expansion stage of an air liquifier, to get that little bit of extra cooling to reach liquid nitrogen temps.

IrC - 4-12-2005 at 20:35

German scientists were playing with these things back in WWII, but ran into problems related to reaching very low temperatures. If there is little differential then they have no efficiency, similar to an air conditioner not cooling well when the heat outside is so high the high side condenser coil cannot radiate very well. Years ago I played with one I built and ran with an air compressor. If there ever was a fun mad science project this one should be high up on the scale.

Quote from a link below: "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."

Following are some links:

http://www.exair.com/vortextube/vt_frmain.htm

http://jnaudin.free.fr/html/vtxtech.htm

http://ucalgary.ca/~kmuldrew/cryo_course/cryo_chap14_1.html

http://groups.yahoo.com/group/mad_scientist/links/Air_contro...

http://www.oberlin.edu/physics/catalog/demonstrations/thermo...

Tacho - 5-12-2005 at 02:26

Yes, it works.
I made two prototypes and obtained a 8ºC drop of temperature rather easily. I measured the temperature of the compressed air coming in and the cold air coming out. It’s really hard to avoid a temperature drop, but to obtain a maximum requires some tuning.
The large prototype was made of 15mm copper tubing (12mm internal diameter) for the hot part and a scrap aluminum tube for the cold side. It uses a conic valve made by gluing a cone to a piece of wood (see picture). The smaller one is made of 10mm aluminum tube (8mm internal) and used, as a valve, a cone held in place by... my middle finger.
Both had nozzle “chambers” made by machining acrylic in a drill press. Both used two nozzles.
I could not obtain a larger temperature drop, probably because my pump is a simple diaphragm pump (see pic.). I don’t have a air pressure manometer, so I can only guess the input pressure was about 2 atm. I tried cooling the hot tube with water, but got inconclusive results.
I tried a few different orifice and nozzle diameters, but any difference was shadowed by the instability of the setup.
The thermometers used were LM35 probes connected to digital multimeters as described
here.




edit: Bromic, the little demons are kept in the brown flask seen in the top picture on the left. You order them from aldrich-vodoo section.


[Edited on 5-12-2005 by Tacho]

frogfot - 23-7-2006 at 02:47

I've been inspired by this thing for quite some long time since you've did this thread.

Anyway, today I've googled for the theory behind this vortex tube but I couldn't find any real explanation. I was lazy to search too much so I've formulated an own "explanation".. Lets see if people will agree on it.. or maby I've forgot something very basic and just talking bull..

To begin with, all systems want to reach an equilibrium, be it heat transfer from hot to cold, collision distribution, or whatever. Same rules is going on in the vortex tube.

So, in this vortex tube we have two systems composed of moving air.

Lets say system A is the outer vortex, and system B is the inner vortex:



The velocities can be separated into total flow velocities: vA1 and vB1, and vortex velocities: vA2 and vB2. These will be used later to describe kinetic energy (KE) and potential energy (PE).

Basically, we want to estimate KE and PE because these are the values that want to lie in equilibrium:

(KE + PE)sysA <==> (KE + PE)sysB

Knowing basic physics we can put together some equations that roughly describe KE and PE of both systems (correct me if I'm wrong):

System A:
KE = mvA12/2

PE = kT + mvA22/2

System B:
KE = mvB12/2

PE = kT + mvB22/2

where: m = mass of air, v = velocity (see pic above), k = some temperature constant, T = temperature of air.

where: k = some constant, T = temperature of air (in vortex), s = distance traveled by air, r = radius (of vortex)

Additional conditions, that are general for such things are that:

vA2 = vB2
vA1 < vB1

This, together with equations mentioned earlier gives:

KEsysA < KEsysB
PEsysA = PEsysB

Now to better "feel" the obtained relationships above, I have pulled some exact numbers of KE and PE out of my ass (just to illustrate the point):

Beginning (no equilibrium):
System A : KE=10; PE=100
System B: KE=100; PE=100

This means two systems are not in equilibrium, one having higher kinetic energy:
(KE + PE)sysA =/= (KE + PE)sysB

The only variables that can equilibrate between these two systems are velocity and heat (mass of air and vortex radius are constant). I guess that velocity is not equilibrated much due to low friction (not sure). But the main variable to change in both systems is the temperature.

When equilibrating the above figures they may look something like this, here, equilibrium is fully attained:

System A : KE=11; PE=144
System B: KE=99; PE=56

This would satisfy:
(KE + PE)sysA = (KE + PE)sysB

Note, again, the exact numbers are just to illustrate the point.
The PE (temperature) has been changed alot because heat is transferred easily and KE (velocity) is altered just a little due to low friction. Sounds fair?

This way I think that one can get same effect by injecting a high velocity air stream into low velocity air stream (with opposite direction). The only problem would be is a shorter contact time between the two systems, which will result in not enough time to fully equilibrate..

[Edited on 23-7-2006 by frogfot]

EDIT: Stupid sub/sup script!!! They doesn't work... :(

[Edited on 23-7-2006 by frogfot]

Organikum - 23-7-2006 at 03:02

They are terrible loud. Actually the efficiency is directly related to the noise what suggests that there is a sonic component, resonance, in the separation and no devil.

/ORG

[Edited on 23-7-2006 by Organikum]

Mr_Benito_Mussolini - 23-7-2006 at 12:43

Scientific American when it was still good:

About a Remarkably Simple Device to Attain Low Temperatures and Various Other Matter
---------------------
by C. L. Stong
November, 1958
---------------------

SHORTLY AFTER THE END OF World War II word came to the U. S. that the Germans had developed a remarkably simple device with which one could reach temperatures as low as the freezing point of mercury. The device, which was said to consist only of an air compressor and three pipes, immediately attracted the interest of amateurs who had dreamed of performing experiments requiring moderately low temperatures. The details of construction were not available, but it was reported that the device had in effect realized "Maxwell's demon," a fanciful means of separating heat from cold without work.

Among those intrigued by the demon's alleged capture was George O. Smith of Highlands, N.J. Smith writes: The 19th century British physicist James Clerk Maxwell made many deep contributions to physics, and among the most significant was his law of random distribution. Considering the case of a closed box containing a gas, Maxwell started off by saying that the temperature of the gas was due to the motion of the individual gas molecules within the box. But since the box was standing still, it stood to reason that the summation of the velocity and direction of the individual gas molecules must come to zero. In essence Maxwell's law of random distribution says that for every gas molecule headed east 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 of molecules moving faster.

After a serious analysis of the consequences of his law, Maxwell permitted himself a touch of humor. He suggested that there was a statistical probability that, at some time in the future, all the molecules in a box of gas or a glass of hot water might be moving in the same direction. This would cause the water to rise out of the glass. Next Maxwell suggested that a system of drawing both hot and cold water out of a single pipe might be devised if we could capture a small demon and train him to open and close a tiny valve. The demon would open the valve only when a fast molecule approached it, and close the valve against slow molecules. The water coming out of the valve would thus be hot. To produce a stream of cold 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 from hot without doing work. Thus when physicists heard that the Germans had developed a device which could achieve low temperatures by utilizing Maxwell's demon, they were intrigued, though obviously skeptical. One physicist, Robert M. Milton, investigated the matter at first hand for the U. S. Navy.

Milton discovered that the device was most ingenious, though not quite as miraculous as had been rumored. It consists of a T-shaped assembly of pipe joined by a novel fitting, as depicted in the accompanying illustration [left]. When compressed air is admitted to the 'leg' of the T, hot air comes out of one arm of the T and cold air out of the other arm! Obviously, however, work must be done to compress the air.
"The origin of the device is obscure. The principle is said to have been discovered by a Frenchman who left some early experimental models in the path of the German Army when France 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. Hilsch made some improvements on the Frenchman's design, but found that it was no more efficient than conventional methods of refrigeration in achieving fairly low temperatures. Subsequently the device became known as the Hilsch tube.

The Hilsch tube in the illustration is constructed as follows. The horizontal arm of the T-shaped fitting contains a specially machined 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 a small opening which is connected to the leg of the T. Thus air admitted to the leg comes out of the opening and spins around the one-turn spiral. The 'hot' pipe is about 14 inches long and has an inside diameter of half an inch. The far end of this pipe is fitted with a stopcock which can be used to control the pressure in the system. 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 central hole of which is about a quarter of an inch in diameter. Washers with larger or smaller holes can also be inserted to adjust the system.
"Three factors determine the performance of the Hilsch tube: the setting of the stopcock, the pressure at which air is admitted to the nozzle, and the size of the hole in the washer. For each value of air pressure and washer opening there is a setting of the stopcock which results in a maximum difference in the temperature of the hot and cold pipes. When the device is properly adjusted, the hot pipe will deliver air at about 100 degrees Fahrenheit and the cold pipe air at about -70 degrees (a temperature substantially below the freezing point of mercury and approaching that of 'dry ice'). When the tube is adjusted for maximum temperature on the hot side, air is delivered at about 350 degrees F.

Despite its impressive performance, the efficiency of the Hilsch tube leaves much to be desired. This perhaps explains why no one has mathematically analyzed its operation. Indeed, there is still disagreement as to how it works.

According to one explanation, the compressed air shoots around the spiral and forms a high-velocity vortex of air. Molecules of air at the outside of the vortex are slowed by friction with the wall of the spiral. 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 the outer layer of the vortex transfer some of their energy to this layer by bombarding some of its slow-moving molecules and speeding them up. The net result of this process is the accumulation of slow-moving, low-energy molecules in the center of the whirling mass, and of high-energy, fast-moving molecules around the outside. In the thermodynamics of gases the terms 'high energy' and 'high velocity' mean 'high temperature.' So the vortex consists of 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 a secondary effect which takes advantage of the fact that the temperature of a given quantity of gas at a given level of thermal energy is higher when the gas is confined in a small space than in a large one; accordingly when gas is allowed to expand, its temperature drops. In the case of the Hilsch tube the action of centrifugal force compresses the hot rim of gas into a compact mass which can escape only by flowing along the inner wall of the hot pipe in a compressed 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 of the hot pipe. In contrast, the relatively cold inner core of the vortex, which is also considerably above atmospheric pressure, flows through the hole in the washer and drops to still 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 its commercial application. Nonetheless amateurs who would like to have a means of attaining relatively low temperatures, and who do not have access to a supply of dry ice, may find the tube useful. It will deliver a blast of air 20 times colder than air which has 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, to chill photomultiplier tubes, or to operate diffusion cloud chambers. But quite apart from the tube's potential application, what could be more fun than to trap Maxwell's demon and make him explain in detail how he manages to blow hot and cold at the same time?

[Edited on 23-7-2006 by Mr_Benito_Mussolini]

1958-11-01.gif - 49kB

Magpie - 23-7-2006 at 19:11

I agree with Tacho that this seems like an incredible device! If I understand it correctly it is separating fast and slow molecules that are found naturally in a gas due to the Maxwell distribution of velocities. If this device would have been known in the late 1800's it would have provided tremendous support for Maxwell, Boltzmann, and Gibbs who believed in such an atomic view of matter. There was, however, at that time prominent scientists who did not, such as Mach and Nernst.

I just learned this from perusing some of the articles provided by links that franklyn posted uner the "Entropy" thread. Also covered there is Maxwell's Demon as well as other similar puzzles.

Hilsch tube

Endo - 26-7-2006 at 11:07

I have actually read about the thermodynamics involved with this in an old back issue of scientific american. They had a monthly column about the amateur scientist or some such. They also had several useful graphs detailing the changes needed in hole sizes to optimize this for either hot or cold output. If someone has access to back issues of Sci-am it contained a lot of information that could be very useful in making/optimizing a vortex tube.

Endo

It's almost 2 years later...

Shingoshi - 27-4-2008 at 02:03

Quote:
Originally posted by Organikum
They are terrible loud. Actually the efficiency is directly related to the noise what suggests that there is a sonic component, resonance, in the separation and no devil.

/ORG

[Edited on 23-7-2006 by Organikum]


And I came to the same conclusion as you have. Any system of this type, whether gaseous or fluid, must take into account the principles of acoustics and harmonics to account for the performance of said system. Basically, we're dealing with an advanced form of air-horns. Whatever is required to achieve greater volumes in sound, will directly influence the temperatures produced.

I am very grateful for this site, and the discussions that are provided here. Let's change the world!

Hopefully for the better,
Shingoshi

/edit: I think it should be mentioned, that there is no requirement here that only one type of gas be used in this system. Nor is there any requirement that the system operate with only one gas. Furthermore, neither is there a requirement that the operating medium be a gas at all. It is indeed quite possible to use a combination of gas and fluid as the operating medium.

[Edited on 2008.4.28 by Shingoshi]

chemrox - 27-4-2008 at 23:46

Since you have flow you have work being done no mystery there. I wonder if you had two diameters of tubing the hot would go out the larger diameter to conserve the momentum of the fluid?

12AX7 - 28-4-2008 at 08:26

High pressure, reasonably incompressible fluid I'm pretty sure would cavitate quite nicely around the nozzle. My gut tells me density and viscosity would prevent the hot stuff seperating from the cold stuff very easily.

Tim

unionised - 28-4-2008 at 11:21

An odd thought has just struck me. These separate gas into 2 streams according to the energy and/ or the momentum of the molecules. Do they separate mixtures to any extent? Is one of the output streams richer in O2 and the other in N2?
Anyone in a position to do the experiment?

12AX7 - 28-4-2008 at 13:01

I doubt it. My proof: the AEC isn't regulating them. ;)

Tim

chemrox - 28-4-2008 at 14:23

But you've got to admit it's an intriguing idea and why not? If density why not mass too?

Gases for the masses...

Shingoshi - 29-4-2008 at 02:40

Quote:
Originally posted by chemrox
But you've got to admit it's an intriguing idea and why not? If density why not mass too?


That's exactly the point I was raising about using more than one type of gas. This system doesn't care what's pumped through it (as long as it's not highly-corrosive).

So think of taking two gases, one with a heavy molecule and one with a light molecule. The heavier gas molecules will move to the perimeter of the tube due to centrifugal forces. This will leave the majority of the lighter molecules in the center, giving up their excess energy (in heat) to the larger molecules on the perimeter. Using such a system would only enhance the efficiency of it. The heavier molecules having greater mass, can absorb more heat from lighter ones. This is an advantage not possible in a single gas system.

Shingoshi

ShadowWarrior4444 - 9-5-2008 at 13:28

I believe some newer more energy-efficient refrigerators using a vortex cooling system driven by an ultrasonic transducer, though I'm not entirely sure where I saw this information.

A wee reference: http://en.wikipedia.org/wiki/Thermoacoustic_hot_air_engine

Shingoshi - 14-11-2008 at 23:33

My deepest apologies to everyone with whom I previously communicated here. I hope that I will be back for good now.

Shingoshi