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Pressure vessel, with a insulator

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Andy

Fri Aug 30 2013, 02:38AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi
I would like to put a genny into a pressure vessel with a inert atmosphere under pressure at 230psi. What would be a good insulator for the connection coming out of the vessel, or good fibreglass be used at that pressure, or would it have to be steel?
I'm open to other ways to increase the pressure, with the setup being isolated apart from two leads.

Thanks

Sulaiman

Fri Aug 30 2013, 06:38AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

At >15 atmospheres you would be making a bomb !

I suggest using oil instead, better, cheaper (pressure vessel/sealing costs) and MUCH safer.
ANY oil will be better than 230 psi gas.

OR use parafin wax which wouldn't require a sealed vessel and can be fairly easily melted for repairs etc.
The melting temperature of parafin wax is so low that it will not harm electronic components.

Andy

Fri Aug 30 2013, 07:20AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi Sulaiman
Yeah oil would be good, just worried about friction, the plates hopeful would be 0.5mm separation just thought that oil would cause to much problems. I might have to think about this abit more...
Thanks for the ideas

Patrick

Fri Aug 30 2013, 02:26PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Are these moving?

Andy

Fri Aug 30 2013, 09:12PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Hi Patrick
Yep, but I want be building it, I can't make something to that tolerance :( :)

Eleccentric

Fri Sept 06 2013, 10:46PM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

Hello Andy.

I'm guessing that this thread is in direct relation to one you started here:

I'm not sure why you never come right out and name the type of "capacitive generator" you have in mind, but in reading that thread I was pretty sure you were referring to influence machines - electrostatic generators of a type widely used in the late 1800's and very early 1900's. Now that you've posted about running such a machine under very high pressure insulating gas I'm even more certain. Have you picked a generator configuration? I'm fond of sectorless Wimshurst machines, though there are almost endless possible variations with other obscure names: Voss, Bonnetti, Holtz, Wommelsdorf, etc.

There was some real work done in the 1940's and 50's regarding doing just what you propose. Efficiencies of about 95% were achieved, if memory serves. However, the experiment I recall specifically used hydrogen as the insulating gas, at many atmospheres of pressure. Building one's own pressure chamber is hard enough, but doing it in a way that will hold in hydrogen - with rotating mechanical feedthroughs - in the presence of a few hundred thousand volts sounds dangerous and "out-there," even compared to the usual projects on this forum.

There are a variety of published papers on how this sort of contraption was built and tested. I haven't read them, but I can find references to them.

I don't think oil would be a suitable alternative to gas due to its viscosity and the resulting drag. The only practical reason (yes, I know, practicality has little meaning here) to build this thing is the very high efficiency in converting mechanical energy to electrical energy, and oil would drag that down. Perhaps a good first test would be to submerge a normal air-insulated 2-disc generator in oil and see if it still works well.

All that being said, I do have some useful info to offer. Oceanographic work routinely uses plastic pressure housings for depths with pressures far greater than 230psi. This doesn't directly relate to doing the opposite with the same materials, but it does suggest that the material doesn't matter so much if it is made thick enough.

For materials that would be a more direct substitute for steel, a google search has returned with fiberglass-wrapped polyethylene tanks rated to 150psi, which is promising. More looking reveals that kevlar fiber composite vessels are available for working pressures of as much as 5000psi. These are listed on the sort of sites that never mention prices, of course.

For simplicity (lol) I'd suggest using a magnetic drive linkage to avoid the most mechanically difficult part - a rotating feedthrough.

This was my first post on here, hope I didn't do anything wrong..

Andy

Fri Sept 06 2013, 11:52PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi Eleccentric

Thanks.
The fiberglass-wrapped polyethylene tank would be the ideal way to go. How would you go about stopping a gas leak with a cable going through the wall?.
I was thinking maybe steel with a rubber casket to make both ends insulated, but that might have leakage.
Nice idea about the magnetic drive linkage.

Eleccentric

Sat Sept 07 2013, 12:49AM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

I'd use an off the shelf electrical feedthrough bulkhead connector sold for marine pressure vessels, but installed backward. Teledyne Impulse sells such things rated at up to 750 volts, but that is for use with a metal casing and under enormous pressure in seawater, so you should be able to push things much further in air.

Sulaiman

Sat Sept 07 2013, 06:01AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I didn't realise that you meant a rotating generator, liquid and solid dielectrics are definitely no use;

A few random thoughts;

Sulphur hexafluoride is a widely used dielectric gas, but I think that as others may copy your work if it is successful then it is better to not use such a potent greenhouse gas.

I use butane gas as a dielectric for my P6015 h.v. probe, seems ok.

To get around the problem of a rotating seal you could use rotating neodymium magnets on the outside to rotate magnets on the inside.

If you use magnets to transfer the rotational energy there will be a large axial force on the generator shaft
which could be balanced by using rotating magnets at both ends of the internal shaft
or rotating at one end and at the other a static magnet externally.

Andy

Sat Sept 07 2013, 07:47AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi Eleccentric

I checked that site out and others with wire feed through, the component has the voltage rating, but not the amps, the most I saw was 58amps/600volt.
I think I'll ask a machine shop and see if they could make something that could handle 640mm2 cable.
Thanks

EDIT
Yeah the threads are related. I can get a large supply of firewood cheap, I'm trying to change that into electricity one idea was a steam turbine to drive a cap genny, they other make methanol and run it through a fuel cell, they both need a good switch at high volts or high amps.

Hi Sulaiman

I will be using a solid dialectic, I've purchased some Barium titante and will mix that with fibreglass to cover the plates, about 1mm deep. My multimeter capacitor setting got fried , but will get another one to see if the stuff makes any difference. I will have a look at butane, just might be difficult to pressure it with a off the self compressor.
Thanks

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