How to remove heat from a copper wire magnet?

[MitchellJames]

One of my current designs requires standard open center magnet coil cylinders inside the vacuum chamber.
About 5 cm long, 1cm dia open center, 1 cm coil thickness. It is a standard solenoid.
I was going to remove the heat by wrapping a 3/8 copper water tube around it. This would work well if convection was available however this is in the vacuum chamber. The copper tubing is not going to touch anything but an aluminium sheath holding down the solenoid. So conduction is going to be minimal. That leaves radiation which sort of implies that the copper water tubing is not going to be worth the bother.

What are some good cheap ways of cooling standard copper coils?

Is there a vacuum rated thermal paste?

[Tom Ligon]

Mitchell,

Long time no see!

An old rocket scientist buddy of mine designed a ceramic rocket engine with no nozzle cooling, with copper wires embedded in the nozzle for reasons he refused to specify, and with a tri-propellant rocket fuel (which may have included boron hydride ... not nuclear though) and he estimated would reach a 12k exhaust temperature.

I wanted to know just exactly how he intended to cool the engine. His cryptic answer was MHD and thermal emissivity.

I can't imagine the cooling jacket will do you an ounce of good unless you circulate it to the outside of the chamber. Phase change material (possibly a wax or a low-melting metal) might allow the coil to run slightly longer per test, at the cost of a really long cooling period for radiation.

Otherwise the only advice can offer is to make the outer surfaces of the magnet and the inner surface of the chamber black. Cooled chambers are common, and that should help marginally.

[tombo]

A common way of removing large amounts of heat from a coil it to make the coil from copper tubing with cooling water flowing through it.
It might not need to be 3/8" dia as water removes a lot of heat.
You might need fewer turns though or if you need lots of turns perhaps you could put the conductors inside the tube of cooling water.

[Nik]

Just curious-- How much power must this dissipate, and what stagnation temperature must it tolerate ??

Can you co-wind some coolant tubing with the coil ? Could you manage with foil or laminates to transfer heat to the mountings ?? Can you break the windings into sections, and remove heat at their tappings ?? Can you enclose the entire coil and pump coolant through casing ??

Do PC 'heat-pipe' coolers offer an inexpensive route ??

[MitchellJames]

The Texas summer heat has driven me out of the garage so I am spending more time working on design instead of on infrastructure which means that I am at a computer and have time to post messages at least until it cools down.

The copper water coils are running out of the vacuum chamber to a chiller. The chiller is looped to an outside heat exchanger. I have the parts but none of it is assembled and working. Lots of infrastructure to go. In the mean time I will just use a garden hose if it is not summer. Water from Texas water towers gets more than warm in the summer.

I have seen both 1/8 and 3/8 copper tubing used for coils with water running through them. In all cases these were being used as inductors for old high power RF systems. This required routing the water through conductive and non conductive tubing. A lot of connections done outside of a vacuum chamber using materials that shouldn't be in a high vacuum chamber. Also the loops of the coils did not touch each other. A difficult method to use for a solenoid.

The magnets for this experiment are just standard solenoids, many turns with standard magnetic wire.

I searched around last night and came up with one place that sells 4 oz jars of silver doped vacuum grease for $275 a jar. A little steep for my budget. But the same concept could be used with any thermal conductive material so I am trying to see if I can obtain bulk amounts of powdered diamond or beryllium oxide. I am also going to stick a highly rated computer thermal paste in a vacuum chamber to see how much it out gases. I would like a non electrically conductive thermal grease.

Another way to do it might be to use several loose layers of aluminium foil between the solenoid and the water pipe. A difficult assembly problem since the tubing would have to be wound tight on to the solenoid. I was thinking of winding the tubing on a mandrel and then sliding it over the top which would just crumple the aluminium foil to the bottom. Sounds cheap enough if I can work out an assembly method.

[chrismb]

Can you describe the application? Maybe there is a configuration of permanent magnets that can do the job for you, as it is a fairly small volume you're trying to permeate.

[MitchellJames]

Just curious-- How much power must this dissipate, and what stagnation temperature must it tolerate ??

Can you co-wind some coolant tubing with the coil ? Could you manage with foil or laminates to transfer heat to the mountings ?? Can you break the windings into sections, and remove heat at their tappings ?? Can you enclose the entire coil and pump coolant through casing ??

Do PC 'heat-pipe' coolers offer an inexpensive route ??

As much power as I can stuff though hence the need to remove heat. The temperature has me concerned. I want to run this experiment for hours at a time (steady state). Since this is just standard magnetic wire the temperature needs to stay below what the coating will handle.

Foil would seem the best way to go except that it will leave hot spots where the foil is not compressed against the solenoid. I wanted to fill in the spaces with a thermal grease.

Using a casing is interesting but I am not sure I could implement it with my limited manufacturing capability. Could water be used directly on solenoid wire or would it have to be another type of fluid?

[MitchellJames]

Can you describe the application? Maybe there is a configuration of permanent magnets that can do the job for you, as it is a fairly small volume you're trying to permeate.

Maybe as next step. Right now I have wire, iron, hymu transformer core metal, some power supplies, and vacuum systems. I don't have any highly designed expensive permanent magnets. My wife thinks that I should stay within my budget so I have to use what I have.

[GWW57]

I'm not a physicist, so please ignore this if it is too naive:
why not shift the heat out of the coil using the Peltier effect?

I expect that the effect is too weak to move the amounts of heat produced in your coil though.

[BenTC]

why not shift the heat out of the coil using the Peltier effect?

Do you mean like a peltier device you might put on a CPU? It creates a cold side and a hot side, but the heat from the hot side still needs to go somewhere. Are you placing the peltier so that the hot side is not inside the vacuum?

[GWW57]

Are you placing the peltier so that the hot side is not inside the vacuum?

Yes, I was thinking of long thin thermocouple piles so that one end was in the coil and the other end poked out of the vacuum vessel and could then be cooled by, for example, a water flow. There could then be a hedgehog of lots peltier thermocouples pumping heat out from lots of locations on the coil.

I don't know how efficient modern Peltier devices are though.

[MitchellJames]

peltier junctions don't solve the problem of thermal contact with the coil. The junctions that I have seen are flat surfaced so there would be a much smaller contact area than wrapping the coil with water pipe tubing.

I am leaning towards encapsulation with a design that I should be able to build using oil as the cooling fluid.

[tobiwan]

I am no engineer, but I wiork at a large 1050 mw power plant. Our generators range in size from 320 mw to 150 mw we use hydrogen cooling to circulate in the windings. you can also use ultra pure water in the windings as pure water is non conductive hope this helps.

[MitchellJames]

I was thinking of using liquid nitrogen but decided that was too many complications getting in the way of doing the experiment. Without a good filter system I probably couldn't keep the water pure enough. Oil is used in large transformers. I have some used vacuum oil that I can filter the particulates out of that should work fine.

I have never heard of hydrogen being used for cooling.

[tobiwan]

Yes , it is common practice to cool large generators with hydrogen . it is an excellent coolant , you have to be careful to use nitrogen as a purging gas. So we start with 100% air and purge to nitrogen and then to hydrogen, and visa-versa going the other way so we don't get an explosive hydrogen air mix. hydrogen is not explosive above a 85 percent purity. As an aside we also had a nuclear reactor out here ( now decomissioned) that was helium cooled.