Build - Ranque-Hilsch Vortex Tube

[Feb. 4, 2017]

This is a placeholder page for a future build. Pending an actual build, references will be collected on this page.

Note: Although this is often called a Hilsch tube, the original invention was by by French physicist Georges J. Ranque while German scientist Rudolf Hilsch improved the original design; therefor it seems more proper to call the devise a Ranque-Hilsch Vortex Tube, or more commonly, just vortex tube.

SAFETY WARNING:

Do not underestimate the potential dangers of working with compressed air. Metal components under pressure can come apart frighteningly fast, and can cause severe injury. Wear eye protection at all times, and stand clear of potential debris paths. Do NOT try to hand-hold your vortex tube when operating. See the link below for some real world stores on the dangers of compressed air:

http://www.hobby-machinist.com/threads/respect-compressed-air.56183/

Nomenclature

There are a number of variables which can effect the efficiency of the vortex tube. For the purposes of discussion, the following conventions will be used:

dc = inside diameter of cold orifice

D = inside diameter of hot tube

L = effective length of the vortex tube hot pipe from inlet to the plug

L2 = effective length of the vortex tube cold pipe from inlet to end

n = number of vortex "nozzles"

R = radius of the vortex tube

Here is a simple spreadsheet for calculating important build dimensions for a given tube internal diameter : Vortex Tube Dimensions

Build #1 - Simple, Low Cost Vortex Tube

[Feb. 19, 2017]

My plan is build a number of vortex tubes, starting with a very simple tube and progressing to a more sophisticated build with replaceable parts. This first build is intended to be a "proof of concept" just to make a working (although not very efficient) vortex tube. This tube is made with mostly off-the-shelf parts, so anyone should be able to make one. I used a lathe and mill to build the tube (because I have them!), but it could also be built with basic workshop tools.

It works! While the performance is modest, I was actually able to get some hot/cold differences in operation. The best performance was at the start, before my air compressor reserve was depleted; I also measured with compression coming just from the compressor running. If I had access to a more powerful compressor, I think I would have gotten better performance (see the photos below for the specifications for my compressor).

Ambient temperature = 19.9 degrees C. The chart below shows the temperature differences I was able to attain (all temperatures in degrees C):

Some thoughts about this build: The performance of this vortex tube could probably be improved somewhat by further optimizing the diameter of the vortex orifice and the cold orifice. Using a valve on the hot end might also improve performance. Finally, the vortex chamber could be improved by making the bottom of the plastic plug convex instead of flat, so that the vortex chamber is more perfectly round. However, I will leave these suggested improvements for others to try, as I intend to build another more sophisticated vortex tube.

  • The tube is built from 1/2" nominal (.,577 ID actual) copper tube and copper tube fittings:straight copper tube
  • end cap (for hot tube)
  • copper tee
  • female thread adapter
  • brass reduction fitting
  • brass compressed air fitting

The critical dimensions for the vortex tube are as follows:

D = 0.577"

L = 5.37"

L2 = 1.5"

Cold orifice ID = 0.29"

Vortex orifice ID = 5/64" ().078")

Here is a photo of the parts from the local "big box" store. The total cost of the parts was around $15.

Here is a close-up of the parts. Note the photo includes a ball-valve which I did not use.

I turned a plastic plug on the lathe, and drilled a 5/32" diameter hole for the vortex jet. The plug was held in place in the tube with a brass pin (ground flush with the outside of the tube). The tube was inserted in the copper tee and held in place with medium strength thread-locker. Note the blue line on the tee to mark the position of the vortex orifice. I used thread-locker to fasten all tubing connections (except the end cap), both to avoid heating (and melting the plastic plug), and also so I could disassemble later if necessary.

Plastic plug for vortex orifice.

Plug inserted in tube, with brass pin.

End view of plug; note vortex orifice at 10 o'clock.

For the cold orifice, I used a steel washer from my junk box; I was lucky enough to have one which had the dimensions I needed, but common washer could be used and turned or ground to fit. Instead of a valve I used a copper end cap with drilled holes (4 x 1/8" diameter holes); the vortex tube requires some restriction of flow on the hot end to work properly.

Note steel washer used for cold orifice.

End cap (drilled with holes) is used instead of valve.

Here are the specifications on my Harbor Freight air compressor.

References