Ranque-Hilsch vortex tubes.

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.

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]

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: v_A1 and v_B1, and vortex velocities: v_A2 and v_B2. 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 = mv_A1²/2

PE = kT + mv_A2²/2

System B:
KE = mv_B1²/2

PE = kT + mv_B2²/2

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:

v_A2 = v_B2
v_A1 < v_B1

This, together with equations mentioned earlier gives:

KE_sysA < KE_sysB
PE_sysA = PE_sysB

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]

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]

Hilsch tube

It's almost 2 years later...

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

Tim

Gases for the masses...