The 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 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.

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.

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

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.

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.)

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!

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.

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.

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!

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.

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! )

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!