Another attempt at building a Vortex Cooling Tube

This week I decided to build another Vortex Cooling Tube and run it at home with my compressor. There are a few differences between this Vortex Tube and the last one that I built HERE. This time I decided to use thermocouples to get a more accurate temperature measurement and also I ran this one on a smaller home compressor that has a limited pressure and airflow. Because I knew that I was going to run this one on a smaller compressor I decided to make it smaller. As always the 'garage' attitude and approach to my experiments prevailed in the design so I was limited to materials and tools that I have at hand. Unfortunately this tube didn't work very well for various reasons but I'm blogging about it anyway. Why blog about it you ask? Well because this blog is about the things that I am doing regardless of the outcome! Below is a picture of the materials that I used to build this Vortex Cooling Tube.

 

Vortex Tube Materials

There is some really interesting information about how these things work on the internet and an extensive study HERE for those interested. A simple explanation can be found HERE as well. The idea is tubes like this can separate hot stuff from cold stuff. What is supposed to happen is you put a fluid (usually  a gas) into a tube and get it swirling around (the vortex). The swirling gas travels down the tube to the "hot end" where the hot part of the fluid comes out. Whatever doesn't come out is cooler than the hot stuff and it comes out someplace else (usually the other end of the tube). 
  
Below is a description of what I built with a video of how I went about it.

I won't go into too much detail in writing about this because the video shows the construction and testing and also because this tube didn't work as built. I will mess around with it a bit more to see if I can improve the performance but I actually built two tubes and the second one works better! The second one I'll detail in another blog post once I have tested it more. For now I'll say the second one is even smaller than this one and it's made of plastic. Plastic is a much better insulator than metal and that may be one reason it worked better (or why this one didn't work so well).

  

The brass tube that I used had an I.D. of 0.5" and an O.D of 0.56". To make the cold orifice I used the aluminum rod that has a 0.5" outside diameter and I drilled a 0.18" hole in it for the cold orifice.  This piece makes up the cold orifice plate mentioned in the literature. Once I had the hole drilled in the rod  I inserted it into the end of the brass tube and sealed the small gap between the O.D. of the rod and the I.D. of the tube. I also drilled a 0.25" hole in the outside end of the rod to reduce back pressure on the cold side (watch the video).

   

To get air into the tube I drilled a 0.56" diameter hole in the Delrin block and inserted the brass tube. Once the brass tube was in the Delrin block I drilled a 0.095" hole into both of them as the inlet orifice. This hole is perpendicular to the brass tube and enters the brass tube tangent to the inner wall of the tube. The idea is the air will enter the brass tube right against the inner wall and swirl around the inside of the tube. To get the air into the 0.095" hole I counter-bored the orifice hole and tapped it for 1/8-NPT to accept a pipe fitting. Again check out the video to see what I mean!

  

To make the hot end "cove valve" I again took a piece of the aluminum rod and filed it into a cone shape. The dull end of the cone is approximately 0.1" in diameter and the slope of the angle is about 0.5". I did this by chucking the AL rod in a drill press and used a file against it as it was spinning. The video shows it all and don't try this yourself - it's not too safe!

  

To provide a place for the hot air to come out I carefully filed dimples in the brass tube with a half round file and allowed them to break through into the inside of the tube. This created two outlet ports for the air. When the hot end cone valve piece is inserted into the tube it partially to fully blocks the outlet ports depending on how far it's inserted. This provides some adjustment to the air that is flowing out.

  

The Compressor that I used to test this is flow rated at about 4 S.C.F.M. at 80 P.S.I. That was all the pressure that I could get with the amount of air flowing into this tube. In the air inlet line I placed a Thermocouple to measure the inlet air temperature and it came in at 19 degrees Celsius.

  

Air Inlet to the tube

I also placed a couple of thermocouples at each end of the tube and adjusted the hot end cone valve to give the maximum cold-hot temperature difference. This turned out to be when the valve was restricting almost the entire flow. The temperature difference was only about 5 degrees C! Yuck!! I think the cooling effect seen here is due mostly to the change in pressure of the air as it comes out of the tube and not in any physics magic going on inside the vortex tube itself. At the end of the video I pull the cone end valve out of the tube and the cold end temperature rapidly went up to ambient inlet temp. Again I think this is just because without the cone end block there was little flow resistance on the hot side so almost no air was flowing out the cold side.

 

Vortex tube temperature measurement

  

Below is the video of the construction and testing of this thing. It was a lot of fun to build and an interesting experiment. I'm probably going to modify it and see if I can get better performance. Some of the things that I want to try are insulating the tube, changing the cold air plate diameter, changing the length, increasing the flow and pressure. That last one will require a bigger compressor and will probably give the best improvement. The brass tube conducts heat really well so it may be dissipating any heat that the hot end has. Insulation may help with that. Changing the other dimensions may help as well but I think experimenting and trying different things is what I'll have to do.
 

 

As I mentioned above I built another tube from plastic that is smaller and worked better. I'll write a post about that one once I have time to play with it more. Check back!