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Dielectric oil flow

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Adam Munich

Mon Jan 24 2011, 03:22AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I can't find any info on why this

happens. Does anyone here know? I'm assuming it's black magic.

Mattski

Mon Jan 24 2011, 04:10AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

My initial guess is that it's due to vibrations in the wires and various components which is caused by magnetic attraction/repulsion due to the AC current, or vibrations coupled into the tank from the output wire if an arc is being drawn.

What frequency is it running at?

Maybe in person it is easier to see, but if you put some floating particulate in the oil (maybe some ground pepper) then we can see a little better in the video what is going on.

Adam Munich

Mon Jan 24 2011, 04:25AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I would make another but it's kind of late. Pretty much the oil is flowing in a vortex motion, flowing from the HV side and then spinning around the first stage capacitors. It's definitely not vibration, 30kHz.

This thing makes a HUGE EMF field. I'm 3 feet away and I can feel myself get charged up from the ionic wind. Then I touch a doorknob and get a nice shock. And this is only 45kV!!

PS: Icanhazcheezburger made $30 million!!! I'm jealous and angry at the same time.

Xray

Mon Jan 24 2011, 05:38AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

I've seen that phenomenon many times before when testing X-ray heads in a bucket of oil. I believe that it's caused by electrostatic forces on the oil. The same thing happens with solid insulators such as paper or plastic, only the motions are different of course. This motion of the oil actually helps to cool the X-ray tube by circulating the oil around in the confined space of the X-ray head.

Adam Munich

Mon Jan 24 2011, 12:02PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Yes, but I'd like to know what goes on at the molecular level.

Dr. Shark

Mon Jan 24 2011, 05:06PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

No clue really, but here goes my guess. This would not happen if there was no charge transfer between the oil and the wiring. Thus there have to be some impurities in the oil, maybe moisture, maybe just fragmented oil molecules. Anyway there have to be some molecules that can "ionize" (for lack of a better word) into anions and cations. These will migrate to the anode and cathode of the multiplier, dragging the viscous oil with them. There they get discharged, in the case of moisture even creating trace amounts of H2 and O2, but since the current is so low probably not enough to create any gas bubbles.

PS: Informative thread title, keep it up!

Proud Mary

Mon Jan 24 2011, 05:42PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

According to A A Zaky et al 1967 Br. J. Appl. Phys. 18 953
Electrohydrodynamic motion of the surface of an insulating liquid in the vicinity of a stressed gap

"When a static electric field is applied between two electrodes immersed in a liquid dielectric, the free surface above the electrodes is set in violent motion. This motion does not depend on the polarity of the applied voltage, but appears to be associated with the presence of regions of high-field non-uniformity in the gap. The surface disturbance was recorded by a cine-camera and a number of frames distinctly showing typical movement patterns are given."

It is my understanding that the movement of an electrostatically stressed dielectric fluid is analogous to the ionic wind produced at the tip of a highly charged point - a 'region of high-field non-uniformity' as Zaky says.

Adam Munich

Mon Jan 24 2011, 05:44PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I don't think it's entirely that because the flow is petty substantial, and it becomes vigorous at higher voltages. At 70kV it's like a torrent. It'd take a lot of ions for that to happen, and if the oil was that conductive the multiplier would likely fail.

Gahh PM got a ninja post in...
Then how does that explain this?

Proud Mary

Mon Jan 24 2011, 06:04PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

This is clearly what is going on with the transformers in Xray's oil bucket posted above:

Journal of Electrostatics Vol 7, August 1979, Pages 361-372
J.D. Crossa, M. Nakanoa and S. Savannisa
Electric stress induced motion in transformer oils under 60 Hz stress Journal of Electrostatics

Abstract
The results of an experimental investigation of the onset of electrohydrodynamic motion in transformer oil between metal electrodes is presented. It is shown that under d.c. stress the onset of motion is in good agreement with the theory for unipolar injection of positive charge carriers. Under 60 Hz stress the time delays between voltage application and the onset of turbulence are explained in terms of the production of a critical space charge density in the vicinity of the injecting electrode.

radhoo

Mon Jan 24 2011, 06:29PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Could you post some pics showing the other side of your PCB ?

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