3D printed vortex tube for spot cooling Answered
These tubes are available as industrial supplies by the dozen but quite costly.
Tried a few designs available on the net but either they are next to impossible to print using FDM or fail to provide any significant temperature difference.
Just to be clear: If amient air temp is 25°C then I would like to get below zero on the cold end.
And well, I would like to be able to salvage a small fridge compressor with considerably less air flow than a shop compressor.
Now to the problem(s) I face:
1: The temp on the cold end is affected by both the length of the tube and by how much air can escape on the hot side.
Makes finding a suitable diameter and length quite tricky if you don't have fancy simulation software at your disposal :(
2: The standard cylindrical design for the "engine" is not really that efficient :(
To make them work a lot of pressure is required, usually they won't do anything below 85PSI and most require about as much air volume as a little air grinder.
3: 3D printed parts with complex insides are a true pain to clean, seal and make sturdy enough to last more than a few minutes under these conditions.
I am currently experimenting with PETG as it is a bit more temp resistant and stronger.
My understanding of these vortex tubes is that the outer vortex, created by the engine, travels up the tube.
At the outlet valve the vortext is split so that the fastest and hottest air escapes while the colder air is directed dow, through the outer vortex and at a significantly lower speed for the rotation.
Scientists can't really agree on the directions and spin of the inner and outer vortex :(
My theory is that the hot air is created by a pressure increase towards the end of the tube.
As this also expands the air, the inner vortex will be choked off so to say.
Only option for it is to go through and by doing so loosing a lot of pressure on the exit - the stream cools down.
The circulation around the vortex spin however means that speeds of well over the speed of sound are reached.
I can only assume that at this speed there will also be some energy exchange happening based on the static electricity created where the two stream "rub" against each other.
So far only models with a finely sanded inner tube actually performed at all.
Will one day have to try using a thick plastic straw as a liner...
1. Do you think a complex, conical nozzle is required?
The commercial ones all use them.
However I tend to think that a slotted approach might be better.
Instead of adjusting the gap of the needle valve two half cylinders with slots can create a finely adjustable outlet.
Way easier to desing if all parts shall be printable....
2. If 1 is not a a real requirement:
How to best design the slots for the correct air flow??
In the direction of the rotation?
Or even against the rotation so the air will be forced out onlyby the pressure but not by direction?
3. Is there any easy workaround for Sketchup that would allow me to create sphere with the required channels along the inner wall to create a fast vortex?
I can do screw, nut and bolts, a sphere is no problem either.
But I can't seem to find a way to comine both techniques so they work on the inside of a sphere :(
Why a sphere you wonder? ;)
I like harmony for these things a an egg or a sphere is way more harmonic than a cylinder.
On top of that it would allow to create a vortex to my specs instead of chance.
Ideally the "threads" would get a smaller pitch with every turn.
This forces the airstream to not olny increase in speed (decreasing diameter) but also to be "compressed" before even entering the tube section.
The inner stream would pass through a tube inside this sphere, after passing through the tiny gap the upgoing airstream created.
My hope is that such a design would allow for the low flow rates of a fridge compressor while being quite small in size as well.
Anyone with good ideas or tips?