Transporting an electric charge using moving oil

The pros in this business built pelletrons. They had chains made of alternating metal and plastic links, instead of the Van d Graff belt. The metal links could carry a lot more charge to the HV terminal. They charged the chain with a modest HV power supply. The biggest in the world was at Oak Ridge, TN, single-ended with a 50 MV terminal voltage. This one has a magnet in the terminal that folds the ion path 180 degrees. Many other tandem Van de Graff machines are straight-through, and have two chains and the HV terminal is in the middle of the tank. Insulation is sulfur hexafluoride.

Oil isn't going to carry much charge, unless you dope it with something, maybe little particles of some polar stuff. Or, maybe, tiny wire fragments. Then, the charge has to REACH the particles, THROUGH the oil, which I think wrecks the whole idea. You don't want a very good insulator to interfere with the charge transfer.

Jon

Maybe. Millikan's oil-drop experiment relied on charging oil, but he only got a handfull of electrons on a droplet.

There are oil-miscible semiconductors, you could flood a bit of your oil tubing with UV light and create photoconduction for a short period (long enough to get charge diffusion). The problem, then, is that the charge will repel, and lie mainly against the tubing walls, which isn't the flowing part of the oil stream. It seems you'll get charged oil in motion with gravity streams easier than in pipes.

This is a question for people with electrical knowledge, especially in the field of electrostatics. It's also spontaneous. I'm not sure if I'm going to build anything yet.

A few years back I built a Van de Graaff generator. It occurred to me at the time that it would be really cool to transport the electric charge using a liquid instead of a moving belt. I thought of pumping bubbles of electrically charged air into a column of oil and allowing them to rise under gravity. But then I did a few calculations and came to the conclusion that you could barely generate enough current from such a system to build a good generator, so I never built it.

This week I acquired one of these chemical pumps when a laboratory was being cleared out (in the 0.25 kW size):

So today I was thinking: would it be possible to impart an electric charge to insulating oil (no bubbles this time) and pump the oil up the column of a Van de Graaff generator to transport the charge? If it was all made from transparent acrylic, it would look really cool.

Would it work? How could the oil be charged? Perhaps by pumping it through a stainless gauze connected to a high voltage power supply, I was thinking.

Anyone know? For now, it's just a train of thought. But it's interesting...

All the best,

Chris

=============

-jsw

Are you thinking Jacob's Ladder/spark gap? If so, I'd think the discharges would melt the acrylic tubing in short order.

RE: The oil, I don't think this guy would like it one bit.

Not a clue. But how would you insulate the motor from the charge in the first place?

About 20 years ago I worked with a physicist, he thought this might work. So as his tech I proceeded to build a Van de Graaff with oil as the medium to move the charge, We used a sump pump to pump the oil. It didn't work on the first try, and there was no attempt to alter it to make it work. I don't know if he figured out a flaw in the idea, or, if we decided we needed to go back to money making work. I was disappointed, it was just dropped with no further thought. We did use a high voltage power supply as you suggest above. Mikek

Hi Mike,

That's interesting to hear that someone has already tried it. I'd be keen t o hear a little more about the details of the design and materials, if you can recall them. There might be a fundamental problem, but it might just be a minor design issue which could be resolved.

Best wishes,

Chris

Hi Larry,

No. I'm thinking of machine which resembles a Van de Graaff generator. There would be a rounded aluminium terminal on the top. Like this:

The parts of the pump which contact the liquid are entirely plastic (PVDF). This is what set me thinking about the idea of a Van de Graaff with pumped oil again (I first thought of the concept with bubbles around 2001).

Chris

Thanks for the thoughts. Why can't oil carry much charge, but a nylon belt can? I don't doubt your answer, but as more of a mechanical guy, I'm not su re of the reason.

A couple of days ago I was thinking that it might be possible to mix the oi l with thousands of tiny plastic balls which could carry the charge. Or hol low metal balls, but they might not go through the pump. The pump can cope with a maximum particle size of 3 mm and, depending on the head, can delive r a flow rate up to 60 litres/minute. But charging the balls might be diffi cult.

Chris

Interesting. It relies on flow in droplets, though, doesn't it? It's hard t o make droplets go upwards. Single air bubbles which bridge a narrow pipe, with short regions of oil in between, might work, but I think the implement ation and adjustment would be difficult.

Thanks to everyone for the ideas.

Chris

So you mean a semiconducting liquid which can be mixed with oil? Do you have any product names for these semiconductors? If it worked, it could create a nice show.

Chris

Are you sure? I'll bet the seal is against the metal motor shaft. Plastic wears too quickly. Still, that would give you half an inch of plastic to insulate _how_ many kV? Seems iffy at best.

Wild concept.

There is no shaft seal. The motor is vertically mounted above the tank and a thick plastic shaft dips down into the liquid.

I've tried to follow the answers you've received regarding oil and charge, and I'm not certain you're getting correct information.

Dielectrics, permittivity and so on is an aspect of electricity about which I'm pretty vague, but my recollection is that a high-permittivity material, like the mineral oil used in oil-filled capacitors, polarizes easily with a low charge on the opposing plates, and I would think that equates to a high potential to store an electrical charge. (or maybe it's irrelevant, because polarization is not the same thing as storing a charge)

But, as I said, I've always been a little vague about this, being more interested in the results in a capacitor than in the electric charge within the dielectric. For example, although there is a high degree of electrical polarization within the oil, I believe that the net charge is zero. What that implies for the ability of oil to*store* a charge is where I'm vague about it.

Sorry if this just confuses the picture. But I think you need to dig deeper to get the answer you're looking for.

Thanks for the response, Ed. The way I understand it (and this isn't really my field), you need to either tear electrons out of the oil or force more electrons in, so that a net charge is present in the oil rising up the pipe . How one achieves that, and how easily it can be done, I'm not sure.

Ya, I don't remember much. We used pvc riser tube, about 4 ft tall. A possible power supply was 12kV, I don't recall, but I know we had those on the shelf. I think we used a stainless steel bowl as the accumulator. Sorry can't give you much info. Mikek

It's a pity that your boss never published the details of the test. Do you recall how you attempted to transfer the charge to the oil, and how fast the oil moved? I'm assuming it was transformer oil you used.

Thanks!

Chris

OK, if you say so, that's handled.

How you make a natural insulator (oil) into a carrier for electrons is your next very interesting task. Let us know what you find. (Too bad Mike's guy didn't pursue it.)

Yes, I think you are on the right track. I'm not a physicist, but it seems that a liquid just isn't going to carry much charge. i think it is SURFACES that can carry charge, and these surfaces have to have a distinctly different polarity than what they are surrounded by. Anything works OK if surrounded by vacuum (or air, even). The oil would have to be a VERY good insulator, meaning very clean and dry. The metal balls ought to work, you'd need a metal brush to break through the oil film to charge them.

Jon

Same here. d8-)