Low Tech Gas Feed Solution

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Low Tech Gas Feed Solution

Postby Steven Sesselmann » Mon Jan 16, 2017 10:46 am

Plasma Backdraft Arrester

This high voltage gas feed problem has been driving me nuts, and today I came up with a simple idea which might work.

Basically its like a wine makers glass air lock with a bit of diff pump oil in it. Have any of you guys seen something like this being used before and do you think of the idea, will it work?

Steven
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Re: Low Tech Gas Feed Solution

Postby Rich Feldman » Mon Jan 16, 2017 9:31 pm

Nice picture and nice idea, Steven.

Let's be sure we have the same understanding of "Plasma Backdraft Arrester".
Left side tube connects to apparatus (ion gun?) at high voltage and very low pressure.
You don't want an electric discharge inside the hose, back to a gas flow control at ground potential.
HV isolation comes from the oil column in U-tube, right?

Gas pressure on the source side of U-tube will be on the order of a couple of torr, to support the oil level mismatch. Gas bubbles will expand as they rise through the gradient of hydrostatic pressure.
Don't know how much much they will expand, since surface tension will also be important. How soon will you have a picture for us?

Sparse bubbles probably won't reduce the dielectric breakdown voltage much. Were you ever told that it's dangerous to pee off the side of a bridge, if there are electric train wires not far below?
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Re: Low Tech Gas Feed Solution

Postby Steven Sesselmann » Mon Jan 16, 2017 11:15 pm

Rich Feldman wrote:Let's be sure we have the same understanding of "Plasma Backdraft Arrester".
Left side tube connects to apparatus (ion gun?) at high voltage and very low pressure.
You don't want an electric discharge inside the hose, back to a gas flow control at ground potential.
HV isolation comes from the oil column in U-tube, right?


Yes, yes and yes, that's the basic idea..

Gas pressure on the source side of U-tube will be on the order of a couple of torr, to support the oil level mismatch. Gas bubbles will expand as they rise through the gradient of hydrostatic pressure.
Don't know how much much they will expand, since surface tension will also be important.


Well all of this will depend on the viscosity of the diff pump oil, but from what I have seen before the synthetic oils have a low viscosity.

How soon will you have a picture for us?


First I have to mentally prepare myself to dump the electronic gas flow project I spent the last 3 months on, then move on swiftly and find some Swagelok to glass fittings. I have a local glass blower just up the road who can make it for me.

Sparse bubbles probably won't reduce the dielectric breakdown voltage much. Were you ever told that it's dangerous to pee off the side of a bridge, if there are electric train wires not far below?


If I ever feel the urge while crossing a railway bridge I shall remember not to do any target practice :)
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Re: Low Tech Gas Feed Solution

Postby Roberto Ferrari » Tue Jan 17, 2017 12:18 am

Hi
I don’t understand the issue.
With a peek tubing you can feed deuterium to your chamber.
1/16” to NPT Swagelok adaptor would solve the joining point.
Do I miss something?
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Re: Low Tech Gas Feed Solution

Postby John Futter » Tue Jan 17, 2017 12:30 am

Roberto
I have lit up a 30m roll of polyurethane tubing like a giant neon bulb. Pashens law gives us a clue as to why this happens.
I think
Steven is trying to find a way to prevent his terminal voltage being shorted out via this discharge.
however his bubbles will grow in size by 1000's of times as the perceived pressure goes lower in the insulating liquid
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Re: Low Tech Gas Feed Solution

Postby Steven Sesselmann » Tue Jan 17, 2017 12:52 am

John,

Why do you think the bubbles will get that big?

Pressure on the gas side is about the same as on the chamber side, so the gas can't expand all that much. I would still be using the Mass Flow Controller (MKS 649) to control the pressure in the chamber, but this time it will be at ground potential which makes everything so much simpler. The size of the bubbles would be function of the surface tension in the liquid, which I suppose can only really be confirmed by a test.

Steven
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Re: Low Tech Gas Feed Solution

Postby Roberto Ferrari » Tue Jan 17, 2017 4:23 pm

Got it!
Cannot put a grounded metal sieve or mesh in order to drain current to ground while deuterium still goes through?
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Re: Low Tech Gas Feed Solution

Postby Rich Feldman » Tue Jan 17, 2017 7:13 pm

Roberto, Steven is not talking about feeding gas to fusors.
In a fusor, metal fitting at vacuum end of gas line can be grounded. That's not always the case when the gas is for ion guns, particle accelerators, etc.

Steven, I bet John was thinking of the change in hydrostatic pressure from a couple of torr at bottom of oil to low micron level at top. Equilibrium volume of bubbles would change by the inverse factor, except for the extra internal pressure to balance surface tension.

I bet formulas and numbers applicable to our case can be found this paper, with theory and pictures of expanding gas bubbles in microgravity. https://ntrs.nasa.gov/archive/nasa/casi ... 019007.pdf

[edit] Consider a gas bubble of radius 1 mm in water. Surface tension at 20°C is about .073 N/m.
The equilibrium pressure inside the bubble exceeds the outside pressure by 2T/r = 146 Pa. About 1 torr according to this unreviewed analysis.

[edit some more] For a small gas flow, it might help if U-tube were modified to make the bubbles consistently tiny and frequent. This picture shows about 1 sccm of air bubbling through water at about 1 atmosphere.
bub.jpg
as presented here: viewtopic.php?f=6&t=8725&p=60017 Next round should have vacuum on the discharge side.
Last edited by Rich Feldman on Wed Jan 18, 2017 12:28 am, edited 1 time in total.
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Re: Low Tech Gas Feed Solution

Postby Roberto Ferrari » Wed Jan 18, 2017 12:26 am

Thanks Rich!
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Re: Low Tech Gas Feed Solution

Postby Steven Sesselmann » Sat Jan 21, 2017 12:05 am

I couldn't resist ...

https://youtu.be/HyWqxkaQpPw

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