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Picture of The Hilsch vortex tube
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The hilsch vortex tube, cools and heats air at the SAME time with no moving parts, and NO electricity. cool huh? it's quite simple, and only a matter of getting the dimensions right! Not to mention the ability to produce EXTREME temperatures! all that's needed is compressed air!

So, let's demonstrate two simple scientific principles through this tube. That's right, two principles in one!

let's start with temperature. Temperature is an AVERAGE of how fast the particles are bumping into each other. Because it's an average, it means that air is composed of fast AND slow particles. It's hot and cold at the same time! (see right of third picture) How will this be proved? Well, I think that if we just separated the hot and cold, that'd do just fine for proving!

How's it going to work? By utilizing inertia! Which is defined as: "the property of an object to remain at constant velocity unless acted upon by an outside force." Basically, once you get a boulder rolling, it's not going to want to stop. And trust me, it'll resist you changing it's velocity!
There are two things that make up inertia- mass, and velocity. More of either means more inertia.

Now imagine, there's a wall that curves 90 degrees. A boulder and ping pong ball are rolling towards it. (see fourth picture for the explanation) now, as you saw, the pingpong ball was just pushed away with ease. Now, say the pingpong ball was the same size as the boulder (but still very much lighter) and on the right instead of the left. The boulder would still force its way to the wall. If you had a steady stream of boulders and giant pingpong balls, and this was a circle instead of just a curve, it wouldn't be long before there were only boulders rolling along the wall, and all the pingpong balls were all pushed to the inside.

Now, one step further, now because inertia = mass x velocity, say you had lots of molecules of the same weight going around that circle. But some were moving really fast, and others slow, because the faster ones are moving much faster (and have more inertia), they'll push the slower ones out of the way. (yes, just like the boulder and pingpong ball) and before you know it, there's the hot (fast) molecules around the edge, and slow (cold) in the center! (see left side of third picture) and that's exactly what the inside of the vortex tube looks like!

to put it very simply all the vortex tube does is get those molecules moving in one direction (rather then the chaotic right of the third picture) so that the separation will begin!

There ya go, you've learned two scientific principles, and the basic idea of how this machine works. If you want to know the history and a step by step process, go to step one! If not, and just want to build, just move to the step after that.

 
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Step 1: History and step by step explination

Picture of History and step by step explination
the history

Georges J. Ranque, a French physicist noticed temperature differences in vortex separators. He found that the center would get cool, and the outside quite warm. After some due thought, he wrote some theories up and moved on. These ideas, as well as maxwell's thoughts on the subject came to Rudolf Hilsch and he began actually researching and building a refrigerant system to try and beat the standard system for the German military. After building a few prototypes, and getting a very good hold on the dimensions, he left the idea alone, as, the conventional system was more efficient, and less noisy.

Ok, enough history, now how the tube actually works in a step by step process. This is for those science nerds who really want to know how the air separates in this cool machine. Be warned, this is complicated, and I tried to explain it as well as I could. If you've got a good enough idea from the scientific principles above, you may just want to go to the next step.


-First you have the vortex chamber, this is simply where the air starts to spin. the better this is designed, the better your tube works. for the best tube, the faster you can get the air to spin the higher the temperature change.

-Second the air moves down the long hot tube and the hot air separates outward, and the cold air is pushed to the center of the vortex. (effects of inertia)

-Third, the air makes it to the end of the pipe, and, because the ball valve is opened slightly, with a small opening near the WALL of the hot pipe, it siphons off hot air, but, because the pressure is too great to go out that single opening, some of the air must rebound and travel through the center of the vortex, and exit back through the hole in the middle of the vortex chamber.

Why wouldn't it just go through there in the first place? simply because in the vortex chamber, the air is moving so fast, it's being smashed on the walls of the pipe and can't "pull" itself to go through it. If the ball valve is closed, enough pressure builds, and the air just exits there, as, there's nowhere else to go. Because the ball valve is slightly opened near the wall where the air is being smashed, it tries to exit there first. If it can't make it out there, it is forced to go back through the center of the vortex and exit at out the cold tube.

-fourth as the air goes back through the center of the vortex, the faster molecules push back out towards the edge of the tube, and the colder are forced to the inside. Because there is too much air to exit out the hot tube, the air is forced to escape out the cold tube, and your separation is complete. hot air out one end, cold out the other.

Now we're done with theory, thank goodness! Back to the hands on build it part!
Next step: the materials!



EDIT: due to many people asking what "practical" use this might serve besides teaching a principal, once tuned to achieve temperatures below freezing, you can use the tube to freeze all sorts of stuff! Scientists use it for tissue sample freezing, what can you use it for? Just think carefully. Because you're producing a concentrated blast of cold air, you can freeze things REALLY quickly! Honesly, if you've got a large air compressor that's just sitting there, this is worth a build. In my experience, uses come after it's built, not before.

Step 2: Supplies and such

Picture of supplies and such
Ok, enough with theory, let's make some hands on reality! One little bit of theory left though...

Possible hot and cold temperatures. If you build this right you get EXTREME differences, no, not a wimpy 90 degrees hot, and 60 degrees cold, we're talking -50 degrees cold and 350 degrees hot! that means you could burn and freezer burn your hand at the same time!

But, not to disappoint, but realistically expect below freezing, and just above water boiling. which is still a huge eye opener for friends!

Down to business, here's what you need:

-air compressor (bigger is better!) if you've got a tiny little few gallon pancake compressor, you will NEED to half all my measurements. These things hog air like no tomorrow! a big stand up shop compressor will be best, but a laydown 2-5 CF compressor will work.
- 3/4", 5" PVC tubing (steel, copper and such do work... but PVC is easy to work with, and VERY easy to cut)
- 1/2 inch thick 4"x8" (or larger) piece of acrylic/plastic. Remember, you CAN sandwich more pieces together to make this piece.
-1/4" fender washer ( doesn't have to be a fender washer, you just need a 1/4" hole in it)
- glue (epoxy)
- ball valve that fits the PVC tubing, you'll probably want a non threaded type.
-plastic/copper 1/4" or 1/8" tube.
-T fitting (can do without, depending on design (just keep reading before you decide to buy this or not) for the tubing above
-on/off fitting for the tubing
-connectors to attach to air line.
-4 or so bolts and nuts, must be longer then 1"

*links are to amazon

Step 3: Design the vortex chamber

Picture of design the vortex chamber
look below at the schematic I made. You'll notice there are TWO types of vortex chambers, the Archimedes screw, and the opposing jet (this is what I used, but I plan to test the Archimedes screw soon)

So, depending on which one you want to build, you may, or may not need the T fitting for the air lines.

the Archimedes screw does NOT need the T fitting. but needs 1/4" air lines
the opposing jet design DOES. can use either 1/4 or 1/8 lines

now, the archimedes screw all that's different about it, is that you need to drill ONE hole instead of two, and you must design the one spin spiral (does not need to be perfect, just has to be smooth)

we'll discuss the two opposing jet design. HOWEVER, please note, the archimedes screw must fit into the 3/4" pipe. Also note that the "two piece washer sandwich" below, is what both of them will be. the indentations are JUST so that the PVC pipes have somewhere to slot into. They're glued in place then screwed together so the washer is sandwiched between them.

Step 4: Hack and slash!

Picture of Hack and slash!
to start, let's cut our pieces up!

first, cut the PVC pipe into two sections, one 24" long, the other, 4" long. Save the rest, you may need it if you screw up.

second, cut your piece of acrylic to size (4"x8") then cut it into two 4x4 squares. Set one aside for the moment...


(please note I used MDF... this is NOT a good choice. I'm regretting it at the moment... just ignore it. it's... brown MDF acrylic replica for all you're concerned.)

Step 5: Drill!

Picture of Drill!
Ok, out come the Forstner attachments!** (drill bits are fine, Forstner are best... and really great for all sorts of stuff...)

take it slow, and in steps, and cut all the way through the MIDDLE of both pieces. you're using 7/8" drill bits, as, the PVC will fit snugly in the holes you drill. Nothing fancy here, just drill straight through.

Now, pull out the ruler** and sharpie** (for you chaps in the UK, and people in the rest of the world, a sharpie is a permanent marker... sharpie brand is the best though. Correct me if I'm mistaken, but for some reason it's mainly a US brand and other countries don't seem to know of them, how sad.) and draw two tangents to the hole you just cut. opposing tangents are best... (see below) this is where we'll be drilling for your air lines. (only one for the Archimedes screw type)

** available at Amazon.com!

Step 6: Drill! (part II)

Picture of Drill! (part II)
This part's a wee bit tricky... those lines you drew, well, using those as a guideline, we need to drill about 3/4ths the way down the line, but not ALL the way. So, pick the drill bit that allows whatever type of air line you're using to fit snugly (test on a spare piece of MDF... er... acrylic) and get to it.

You need to be very careful how you drill this one... if you do it just right, the right side of the drill bit will just scrape the inside of the circle you cut if you drilled all the way down. So just drill both sides.

Step 7: Drill! (part III)

Picture of Drill! (part III)
Measure the outerdiameter of the washer (mine was a little bit under 1 3/8") and pull out the corresponding spade or mortising attachment. The bit should be just slightly larger then the washer.

Here's the deal, drill down with the spade bit until the flat part starts to catch (please make sure the thing is centered first!) once this happens, stop, and pull the spade out. You'll have left a nice circular indention. (if you used the mortising attachment just drill down enough so that the washer can sit flush, or just above being flush.)

we need an indention so the washer will fit flush in there and not interfere with the two halves coming together in the "washer sandwich". so, move on and I'll show you what to do.

Step 8: Dremel!

Picture of Dremel!
Pull out the Dremel* and a flat headed grinding bit* and get to work. Too hard? nope, just be careful, wear eyeglasses* and go at it. use that groove you made with the spade bit as a depth guideline.

With a steady hand, this won't take long at all!

*available at amazon.com!

Step 9: Pipe'n drill!

Picture of Pipe'n drill!
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Now, push the pipe in through the hole and make it flush with the indentation you just made.

Now, it's time to pull out the 1/10" drill bit and drill in that hole again! this will be the actual passage for the air to go into the hot pipe. be VERY VERY careful! how much you damage the inside of the pipe will determine how well your vortex tube works. like before the drill bit should almost scrape the inside of the pipe when it cuts through. Depending on how the previous holes were drilled, you'll have to move your drill accordingly. Drill both sides and then glue the washer into the groove.

CAREFUL!!!

Center the washer FIRST!!! make SURE the hole is centered with the inside of the pipe.

Step 10: Line up and bolt it down!

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Now, if you're careful, you can pull out the hot pipe and re align the holes later... otherwise, you'll have to use the corded drill instead of a drill press (if you were using a drill press).

center up the hole on the second 4x4 acrylic square you set aside and drill four or so holes, and using the bolt and nuts, attach the two pieces. Re-attach the hot pipe (look down the holes and line them up, hard, I know, but you'll figure out a way, such as lighting up the tube with a flashlight or something to make the hole visible) and attach the cold pipe.


Almost there!

Now, just attach the ball valve on the end of the hot pipe (if it's snug, you probably could go without gluing it)

oh, and rig up the air lines! I'd go into detail... but every compressor and air line and fitting is different, so you'll have to figure it out... but it's pretty simple, once you're done, slide the lines into place (if very snug, you don't have to use glue) If you're using copper lines period, glue it.

You're finished! it should look like the one below (if the dimensions look different, good, this was one of my many pipes while trying to make the instructable... and certainly not the last! each and every one gets better! )

Step 11: Running the beast!

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Ok, attach it to the air line (nearly close the ball valve) and slowly open and close the valve until the hot side gets VERY hot. Honestly, this is trial and error here (make sure you're running the tank around 100-150 PSI) you'll get a feel for it though, However, you should probably never get the valve more then 1/4 the way open.

Notice that the more open you get it (to an extent) will make the hot side cooler, but the cold side MUCH colder. when you find that perfect place, and if the tube is right, if you're not careful you'll get some instant frostbite! yikes! Turn it the other way and optimize for heat (more closed) and you may get blistering air out the hot end! However you work it, the pipe should ALWAYS be hot when in use, if it doesn't get hot to the touch, you probably have the valve too open.


PS: I'd share a video, but, it's an unexciting whooshing sound with nothing moving (but the air) playing with it in person however, that's fun! Once you get it working and have a feel for it, think of the possibilities! freeze stuff in seconds!
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Exocetid6 days ago

Unquestionably one of the most confusing Instructables ever written. See earlier questions. This is begging for an exploded parts diagram.

dmagryta1242 months ago

What diameter is the pvc tube? I'm a little confused, you mentioned several different sizes. It says 24" long, but what size?

Jeff.White.235 months ago

TROMPE (air compressor with no moving parts)

+ VORTEX TUBE (heating and cooling with no moving parts)

= CLEAN ENERGY.

https://www.youtube.com/watch?v=SScpJMsCm9c

ItsTheHobbs7 years ago
what does it do?
introThe Hilsch vortex tube
The hilsch vortex tube, cools and heats air at the SAME time with no moving parts, and NO electricity. cool huh? it's quite simple, and only a matter of getting the dimensions right! Not to mention EXTREME temperatures!
But... don't you need an air compressor? that has moving parts right?

There is an air compressor that uses no moving parts! It is called a TRUMPE.
https://www.youtube.com/watch?v=SScpJMsCm9c

so its not productive its just............a..science project
thecheatscalc (author)  ItsTheHobbs7 years ago
Actually, it is productive, if you build it correctly, you can instantly freeze small samples. there are PLENTY of uses, just think what you could use cold air for!
ooooo ican think of two........ no offense, but its not to exciting
thecheatscalc (author)  ItsTheHobbs7 years ago
well, can't expect everyone to think it's exciting... thanks for commenting though.

I very greatly appreciate your work to publicize this amazing invention by Ranque and Hilsch. The key to the greatest inventions is simplicity, not complexity necessarily. This device piqued my interest when I first found out about it on the Internet (another great invention) back in 1997 approx. I believe it is a device with very great potential still waiting to be tapped. There have been comments to the effect that "compressed air" technology is inefficient. This is simply wrong, I think. Compressed air is an excellent means of storing energy. Standard methods of compressing air can be improved and made more energy efficient by one obvious method. Cadillac Aera "concept car" winner 2010, would use compressed air at 10,000 psi, and would get 1000 mile range (estimated). This is not "low tech" or "old tech" that has no current value; quite the opposite. It is so far in the future that people to this day have a very hard time grasping the fact that any vehicle can be powered solely by compressed air, running thru piston drive configuration or preferably rotary Wankel air motors (in-wheel hubs configuration, as used in the Aera concept car). EngineAir Australia Pty. Ltd. has made some good progress with this technology, but has been ignored by the investors needed for further commercialization. The Aera would be nearly silent in operation because rotary Wankel air motors do not "clatter" as do the piston configurations. So the technology is all available, but only needs to be systematized and put into commercial production (not as luxury Cadillacs, but as everyday, utilitarian vehicles, to include VTOL vertical takeoff and landing aircraft for everyday transportation, thus obsoleting roads, bridges and tunnels for personal transportation and everyday family errands etc.). Anyway thanks again for your excellent work on this Instructable and thanx also to Instructables.com, a great site that really gets the imagination going.

jdillon6 jdillon67 months ago

I forgot to mention that new air pressure tanks are available, made with "carbon fiber composite" and/or other high strength, lightweight materials. These amazing new pressure tanks make entirely new transportation systems feasible, whereas in the past, high pressure tanks made of steel were far too heavy to be practical for these applications. In the USA, a company called Quantum Technologies (QTWW stock symbol on Nasdaq) is or was making these high pressure carbon fiber composite pressure tanks, but may have been focusing on using them for natural gas or possibly for hydrogen storage, rather than for air pressure tanks; QTWW may also be involved in military applications that have limited commercial availability (this irritates me because it keeps happening to some of our best new tech). I am not sure what companies if any, are producing this type of tank for pressurized air specifically, or whether the fuel tanks can be used for air (most likely they can be used for any gas, although hydrogen can usually seep through almost anything). Anyway this is a bit off topic because the RanqueHilsch device can be used to assist in air pressurization, but that's not the typical use intended for it.

it works awesome as a coolling system on grinders

Also, just think what you could use hot air for. (And think what can be done with the difference between hot and cold, hint hint.) Yes, it is productive. Thinking it is not productive is what has kept it in the science museum all of these years. Henry Ford stated something to the effect that he "invented nothing," he just put together ideas and devices that had taken decades of peoples lives to develop over thousands of years. Thank you for the positive attitude here. We need to encourage invention, as you are doing.

"Just" a science project?? Please... Don't you think science can be "productive"?

klaney2 years ago
Would it be possible to run this on something more continues, eg a fan blowing into the vortex chamber. It would be significantly weaker i assume but if you loop the hot air output back into the input it would increase/decrease the output temperatures respectively?
jdillon6 klaney7 months ago

'Atta boy!

LamarS7 months ago

Would you mind sharing your feelings about a few things regarding vortex tubes? Firstly, what are the important dimensions you mention regarding effective vortex tubes? Secondly, do vortex tubes scale up well? If one were wanting to make a large vortex tube would they require air compressed to higher pressure, or a larger volumetric flow of compressed air? Thank you!

Thank you for sharing this. I used to use one of these in an automotive repair shop, it was much smaller and completely made of plastic. I cannot remember the manufacturer. I am now back into automotive repair and wish to use one of these again. In your plans you give a list of parts needed but in your schematic there are differences. The main difference is the length of pipe for the project. In your parts list it is 5" but in the schematic it is 24". Please tell me the length and why it needs to be this length. Thank you, Chuck
benbenbeng1 year ago
For non-relativistic speeds, inertia is not dependent on velocity, only on mass.
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I doubt the air is reaching any appreciable percent of the speed of light.
.
Perhaps the intention was to reference 'momentum' instead of 'inertia'?
Otto Belden3 years ago
I have built several vortex tubes of different materials and sizes. There are a fun and interesting thing to build. The most successful one I made is here and is a bit easier to build:
http://ottobelden.blogspot.com/2010/12/another-home-made-ranque-hilsch-vortex.html
I have instructions of how I built it along with a video and some thermal images I took with a FLIR camera showing the temperature gradients. The details of the other tubes I built are also there on my blog:
http://ottobelden.blogspot.com/p/various-projects.html
Scroll down to the Vortex Tube links. I'm more than happy to help folks build these tubes. Leave a comment on my blog or email me!
- Otto Belden
fidgety23 years ago
i have a quick question

on step 6 do you use the drill bit to "route" the holes for your air line and could you just clamp the 2 pieces of acrylic together and drill into the seam where they meet thus "routing" the air line?

thanks
fidgety2
xizero4 years ago
in my humble opinion the cooling is caused by the increase in velocity of the molecules without heating them - they will need to absorb heat to retain the velocity- and that will cool the inner slower molecules that don't need to because they are not moving as fast -- in essence i am proposing another law of physics one that if a molecule is accelerated that it absorbs heat to stay at its new velocity -- if such a law exists please excuse my ignorance as i am no physicist ... kind regards Mark
Can this be done with copper pipe to avoid any possible flammability that might be encountered with pvc?
atzi4 years ago
Interesting article in Vortex and on making one.
You explanation of a Vortex only separates the hot molecules from the cold ones I cannot disprove, but I have read of other theories like this one......

"While one airstream moves up the tube and the other down it, both rotate in the same direction at the same angular velocity. That is, a particle in the inner stream completes one rotation in the same amount of time as a particle in the outer stream. However, because of the principle of conservation of angular momentum, the rotational speed of the smaller vortex might be expected to increase. (The conservation principle is demonstrated by spinning skaters who can slow or speed up their spin by extending or drawing in their arms.) But in the vortex tube, the speed of the inner vortex remains the same. Angular momentum has been lost from the inner vortex. The energy that is lost shows up as heat in the outer vortex. Thus the outer vortex becomes warm, and the inner vortex is cooled."

I bought a Vortex Tube in the 1980's and used it to cool carburetor choke bimetal coils to test them and the choke linkage. Also was handy to cool temperature sensors to test their accuracy instead of waiting overnight or removal and install in freezer etc. Here is a video I did on my old Blue-Point Vortex. http://www.machine-history.com/Vortex%20Tube
ScienceWiz5 years ago
I am really determined to build one of these (I've wanted one since I saw it in a McMaster and Carr mag. but didn't feel like forking over 200 bucks for one) but I have a question about this step.

What exactly am I supposed to be dremeling? After I drill the holes and use the paddle-bit, what piece am I supposed to dremel and what am I trying to remove/smooth/etc.

Please reply if you get a chance, I would be very thankful!

And Great instructable btw, so far this is the only informational tutorial I've seen for making a vortex tube!
I think what he means is that you don't use the paddle bit to dig down and make the indentation for the washer. You use the dremel for that. Most paddle bits have 3 points, one at the center and two on each end.
| __ __ |
|/    \/    \|
Normally, when you drill into wood with them, the center point digs in first, then the two outer points dig in (and the circle appears), then the flat part digs in & starts tearing out wood. Here, the purpose of the paddle bit is just to dig the perimeter of the circle. You're only using those two outer points of the bit. At least I hope that's what he means, since I'm starting the project tonight.
That's the way I understand it as well. Although I do have a cheap and cheezy backup index of spade bits that don't have the scribe edges. They're not good for much though.
I have had on several occasions, the need for a 'stepped' bore similar to the above picture. One of the requirements was that the two bore sizes be concentric.

I find it easiest to start first with the large shallow bore so I still have material in the hole with the centering pilot from the big bit to target the smaller bit with.
apchar5 years ago
Do you drill into the wall of the PVC pipe? Doesn't the washer block the flow of air? It looks like it's right in front ot the air tubes. Are both halves of the MDF (er. acrylic) the same?
qokhan5 years ago
Some about this site.www.erkim.com.tr/Vorteks_Tupleri.html... I made one vortex tube.İts  good and cheapest working on cnc lathe machine .
ScienceWiz5 years ago
I have a question about the Archamedes Design

In the picture, there is a weirdly shaped white space in the center of the design, is this supposed to be cut out? Left intact? or is the white space just unnecissary?

From the look of it, the Archamedes design looks like the Opposing jets but with only 1 tube (that is double the size). Other then the number of tubes leading into it, it looks pretty much the same. If you've had a chance to compare the 2, I would be really appreciative if you could share your findings, and also if you could explain the white space in the Archamedes design..

Thankyou!
And great instructable! Very informative and very well put together
Dutch_Razor5 years ago
 The vortex tube is such a nice concept, in the lab we have an Exair Vortex tube (exair.com) which produces about 5 liter/s air at -30 degrees C.

It's so noisy that without mufflers, I suspect it goes above 120 decibels!
hiatus1386 years ago
"popular science monthly" magazine, may 1947, p. 144 had the article "homemade maxwell's demon blows hot and cold" in which plans are given out to make a Hilsch vortex tube. Required tools are just a drill press.

The plan specifies an input of 75 to 100 PSI
Output is claimed as "hot end too hot to touch, and cold end gathered frost."
A photo is shown with 2 thermometers reading 68 and 110 degrees respectively. the nature of the tube is that it is adjusted to maximize either heat or cold, you can't have both at the same time.

the entire tube is 12 inches long and made from 9/32" brass tubing.

Unfortunately, this issue is missing from Google book search beta, although all the other issues are there.
http://books.google.com/books?atm_aiy=1940&ie=ISO-8859-1&id=9CkDAAAAMBAJ&q=hilsch#search_anchor

The article was reprinted in "mammoth home workshop manual" 1950, by popular science publishing. A great book, chock full of the sort of home handycrafts common in the "mens magazines" of the day. those WWII era magazines like pop. sci, pop. mechanics, mechanix illus. kinda seem to me like Make magazine's eccentric uncle.
www.popsci.com/archive-viewer

Pop sci just released their entire archive online (searchable by keyword).  Found that appropriately named article.

It depends on the settings. For maximum heating and or cooling temperature you can adjust the flow proportions. But for maximum heating and cooling btu's, (different than temperature) adjust for 50/50 flow, and indeed you will have heating and cooling at the same time.

The higher your input temperature the lower your cold temperature and the higher your hot temperature.

 

jp_bosing5 years ago
From my understanding, the air that enters the Vortex Tube passes through some kind of generating device and spins at extremely high rpm's towards one end of the tube. Then an inner vortex of air spins towards the other end and exhausts as cold air. There is a real good flash animation at http://www.stream-tek.com/products/vortextubes/vortex-tube-works.php; gives a good visual on the inner workings of the Vortex Tube.

-- JP
billmc6 years ago
First go down to your local stream and build a "trompe" so as to supply your compressed air. Then apply the heated and chilled air from your Hilsch vortex tube to your favorite Sterling engine.
Pazzerz7 years ago
Here's a question fer ya.... You said in step 11: attach it to the air line (nearly close the ball valve) and slowly open and close the valve until the hot side gets VERY hot. Are you referring to the ball valve as the one you need to open and close, or is it on the air inlet from the compressor?? The two references to a valve has me confused a bit.
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