Hilsch Tubes Revisited

I think one goal is to keep heat from migrating through the tube from the hot end to the cool end. The best way to do this would be to make it from a material with low thermal conductivity, which may be why they use stainless. The hot air is near the outside over most of the length of the tube with the cool air in the center, so that is why heatsinking the whole cylindrical part of the tube might make sense. However, I agree heatsinking the cold outlet itself does not make much sense.

Most refrigerators work more efficiently if the hot side is kept from getting too hot. I do not know enough about the theory of these tubes to say for sure if that is the case here, but it would certainly make sense.

I once bought one of these for an esoteric cooling problem. It was so noisy we decided not to use it.

I was mulling that fine distinction over in my head as well. I think I might have a piece of acetal plastic I could machine as a thread in cold air tube and diaphragm for the cold end.

There seems to be two designs out there. One has a circular passage with angled holes drilled into the main tube. The other has a lopsided cam lobe shaped chamber to spin the air. Any idea which one is more efficient?

The primary benefit of heat sinking the hot output side (the only part which *I* see as benefiting from that) would be the reduction of heat conducted to the cold side and heating the air coming through that.

A secondary benefit would be reducing the discomfort of accidentally contacting the hot output side with your hand when working around it.

If you put styrofoam insulation around the cold tube, you would reduce the heat gained by condensing water onto the tube and thus improve the efficiency somewhat. (Note that this will consume a *lot* of air, so I hope you have a good air compressor -- and good hearing protection. :-)

BTW That might be a benefit of using stainless as the material too lower thermal conductivity.

But, FWIW, I made one once (as an experiment) in which the vortex was formed by a machined piece of brass (the only thing that I was then sure that I could machine), the housing was made from an old pipe union. The two output tubes were 1/2" copper tubing -- both of the same size, but the output end of the hot side had to be pinched down to about the diameter of the cold hole in the vortex assembly.

If I were to make one today, I think that I might make the vortex forming assembly and the housing from Delrin -- minimize the conduction of heat in both directions. Perhaps the same (or PVC) for the cold tube. Copper or aluminum and heat sink fins for the hot tube. And ideally, some kind of muffler on at least the hot side, which is pointed out into the human space of the working environment. Make the hot tube significantly larger than the cold tube, which also benefits with better thermal conduction to the air, and only restrict the output end (a few inches downstream) of the hot tube to the diameter of the cold hole in the vortex assembly.

Good Luck, DoN.

"Bob La Londe" fired this volley in news:zCz7r.62663$ snipped-for-privacy@newsfe15.iad:

Some are made from acetal, Bob -- the whole assembly, not merely one or the other end.

LLoyd

"Bob La Londe" fired this volley in news:n7y7r.13744 $ snipped-for-privacy@newsfe09.iad:

I do, too. Two 'scraps' 4"x12"x18", 6061.

LLoyd

They both are terribly inefficient even if you also have a use for the hot side

wsfe13.iad...

Well, I have one small machine running flood coolant, but I would really like to keep the other machine dry for other reasons. I can build either design for starting the vortex. I had hoped somebody had already experimented with them and knew which style produced a greater temperature differential. I've got the plug design figured out to make flow adjustment quick and easy, and I can use my NCT for checking the output temps. I figured to just use a bathroom vent with auto closing louvers to send the hot air outside and let the cold air lightly pressurize (its not a sealed system) the cabinet.

Yeah. I have seen plenty of DIY ones on the web made out of PVC pipe too. The one under lying thing I have seen in most of those is a substantially lower differential than some of the commercially designed ones claim. It could be design (pocket vs jet) or some other factor like the material its made out of.

--Well howzabout running a Microdrop system; they're *almost* dry; not real cheap tho..

Bob La Londe fired this volley in news:b589d4bf- snipped-for-privacy@to5g2000pbc.googlegroups.com:

I think its the concentricity and smoothness of the bore. The gas has got to get up to almost unimaginable rotations per minute inside there for the differential to be very high. Any minor defect in the walls, or any out- of-round condition would disturb the flow.

LLoyd

That's a condition I had not considered. It makes sense though.

I still wonder if the cam lobe shaped pocket vs the multiple angled jets has a substantial difference. Most of the DIYers are using the multiple angled jets method. Like I said. I can make either one. If I had more time to play I might make both and set them up to used on the same hot and cold tubes and compare. I don't have that kind of spare time right now though.

Consider what might be easiest for you to make first. The cam-shaped lobe sounds like it is calling for some fancy programming in a CNC machine. (But then, you have the CNC machine, don't you?

The way I made mine was to turn a ring near (but not at) the OD of the part to which the cold tube attaches, and then mill slots into the ring so they ended up tangential to the ID of the ring -- then mate that to a flat surface connected to the hot tube. This left a ring cavity just outside that into which air was fed via a tapped hole in one of the flats of the pipe junction.

Enjoy, DoN.

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The ones which I saw which prompted my experimentation with them were being developed for use in a tank (tracked military vehicle, not a container for liquids or compressed air). The cold air was piped into holes in the top of the crew's helmets, to keep at least their brains from overheating.

The two drawbacks of these things -- poor efficiency, and lots of noise -- were not a problem in that environment. Given how much power it takes to move all that forged iron and steel around, and how much noise both the engines and the tracks make, the crew would happily accept the benefit of cool heads. :-)

Sounds as though you can experiment with both, and let us know which works better. But I suspect that the cam lobe design is later, and presumably it either works better, or was designed to get around patent restrictions on Hilsch's designs. :-)

Enjoy, DoN.

machines as the coolant and to blow chips

but that just isn't in my plans if I make

I'd consider a long coil of mini copper tubing inside an ice - filled cooler before I'd consider a Hilsch tube.

--Winston

Or park the copper (or aluminum) tubing inside a mini (or larger) fridge (or chest freezer, I suppose - depends on what you have handy and space available) - enter the fridge section, and exit after a bunch in the freezer section. Drain-leg in the fride section would help with condensation. Quieter and far less power used than with the vortex tube. If it comes out of the freezer at 0F under pressure, it should be quite chilly by the time it expands at the nozzle.

Nice out of (or in) the box solution- I bet the cost wouldn't be much different from buying a commercial vortex tube.

A little muffin fan inside the fridge could help.

Good idea!

Or go cheaper, smaller and colder with a 'saturated - salt ice water' slurry in your ice chest.

--Winston

Ice generally isn't "free"; salt is cheap, but also not free, and can be corrosive to have around the shop; this is something Bob wants to run every day (or nearly), and labor to drain the saltwater and load up the fresh salt and ice also isn't free - so refrigeration wins, IMHO for cheaper.

Smaller depends on the fridge you are using .vs. the cooler, ice source, and salt storage, which can easily be larger than a small fridge.

It can also win on colder -21.1C is only -6F, and plenty of freezers can be cranked colder than that. OF is just a typical setting.

It also wins on less messy.

If it were a one-day deal or the like, I'd agree with you, but I'd choose refrigeration in a heartbeat for any regular use. I'm intimately aware of the hassles of salt-ice refrigeration, and I'm quite certain that if I were making ice cream and sorbet as a busness rather than for myself, it would be an easy decision to spend the money for a refrigerated mixer - for home use it's a lot of money, so I use salt and ice.