Pipe pressure rating

[SillyOldDufferModerator @sillyoldduffer]

Shoot me down in flames if I've got it wrong but I think the maths shows there isn't much to worry about here.

Joe's very impressive capacitor stores 8KJ of energy. In comparison a kg of hard coal stores about 30MJ. His capacitor contains the energy equivalent of less than 0.5 grams of coal.

What makes the capacitor fun is that the energy can be released very quickly. Whilst spectacular, the effects of the discharge will be short range because the amount of energy in the system is relatively small.

I shall sleep easy in my bed tonight!

Regards,

Dave

[frank brownParticipant @frankbrown22225]

More power Igor!

Frank

[mechman48Participant @mechman48]

Way above my head but does Joe page 1 work for or have anything to do with CERN or the Large Hadron collider or in any way connected to Jules Verne's time machine story …

**LINK**

Just can't get my head round this one… … no insult intended of course.

George.

[JasonBModerator @jasonb]

Sounds like a candidate for that BBC program Diane posted about last week

Edited By JasonB on 23/11/2015 20:17:57

[V8EngParticipant @v8eng]

Perhaps Joe has come up with a very complicated way of coating the inside of a steel cylinder with another material (from the wire).

Edited By V8Eng on 23/11/2015 20:20:53

Edited By V8Eng on 23/11/2015 20:21:37

[Nick_GParticipant @nick_g]

[Rufus RoughcutParticipant @rufusroughcut]

Hi Joe

You will find some freely available info for protection against projectile forces for your containment apparatus during failure conditions from the the US military ballistics and nuclear webs, there's many to shake a stick at, but have found them the greatest valuable resource in my former life, I'm sure if your brave enough to tackle these activities in your shed per say, then trawling some of the more sensitive web sites around would be a breeze and I'll say no more.

Good luck

[Anonymous]

I don't think I'd experiment inside, but it shouldn't be a problem outside. Personally I wouldn't bother with trying to contain the results. I suspect it'll be rather unspectacular, a very hot wire that will melt and break the current, albeit possibly with some arcing. Unless the capacitors are pretty special with very low ESR and ESL and the wiring is also very low inductance I doubt that the currents, or di/dt, will be anything like those mentioned.

Andrew

[Clive HartlandParticipant @clivehartland94829]

In any case how are you going to measure the pressures you expect to get? I cannot see a gauge doing it. Perhaps a copper disc being crushed but what parameters are you going to compare the crushed disc to.

Clive

[Joe PageParticipant @joepage27051]

Yeay, finally some people who understand what I'm doing.

Dave – yep completely true, the energy I'm dealing with is so small that it's not much use, as in my example it would power a kettle for 4 seconds, or the same energy in 1/19 of a cream cracker, but because it can be discharged so fast the results are spectacular when shorted through something like a wire.

George- If only I were, but unfortunately I'm unemployed at the moment, quit my stressful machinist job.

Jason – That ain't such a bad idea, but I'm not sure if it could work for me or against me, not sure if I trust the BBC.

V8eng – This method is actually the most efficient method for producing nano particles, something I hope to achieve and prove.

Nick – Probably going to be me later on in life

Rufus – Thanks for the advice, I love researching such documents, still going to make the vessel, but to hold water like a bucket, hydroforming is what I'm doing instead.

Andrew – you caught me, I wondered if anyone would question these numbers. esr and resistance is about 0.1 ohm total, so about 9kA, still a lot of current, but I am using electrolytic's, so quite high ESR's compared to film capacitors. I do have a bank of films that's 34kV, 300J, esr 0.4ohm so peak currents of 85kA, but that's in a different project.

Clive – This is something I'm not sure I can do accurately. Assuming it's in a bucket of water. I could put a copper disc at the end tube dipped in the water, an approximate calculation on the force required to do puncture the copper disc would be made, then see if it punctures.

[jason udallParticipant @jasonudall57142]

Sounds a bit like a chap I saw who built a ( I think it was called a fuzor)..basically internally “nano coated”( I would have said sputtered) spheres..arranged at the vertices of a tetrahedron. .and filled with special goo..then spun…
He carefully built this and set ip live video feed…to wait for the “anomalous” behaviour. .claimed for it….
( some sort of overunity/antigraviry thing)…
..the connection? ..just the how of the sputtering. .fuse wire..cap bank..and splat..

[jason udallParticipant @jasonudall57142]

U tube can have good stuff..too.

One chap built a chemical reactor cell…
Thick wall gas pipe..threaded..end caps..plunger (loose piston)..just long enough to be nipped buy end caps..
Fill with reactants..add piston..screw on caps….bake….
Yields the graphine film. .desired

[jason udallParticipant @jasonudall57142]

Joe..have a look at the reactor vessel’s used for explosive ( or thermal) deburring. .

[jason udallParticipant @jasonudall57142]

Also worth a look is codys lab —atomic drain cover…
Were he recreats on a scale the experiment conducted by the atomic energy dept. Of putting nuke down a well..and launching a drain cover…
From a period when the world had just discovered nukes and needed to play

[JAParticipant @ja]

I am not sure about this at all. The energy release is very high but over a very short time period. OK the theoretical pressures are high for a fraction of a second but then nothing. By the time the pressure vessel starts to respond the pressure will have gone. Perhaps a tin can will do.

Or have I got this all wrong.

JA

[jason udallParticipant @jasonudall57142]

JA…8KJ is 8 kJ however fast or slow its delivered.

8KJ as has been said equates to say 20Watt light bulb for 400 seconds….
In comparison mobile fone battery. . 2 amp hour at 3V..60*60*2*3= 21.6 KJ

Edited By jason udall on 24/11/2015 16:04:03

[jason udallParticipant @jasonudall57142]

I wonder..
If you take a sphere of say steel..and a given wall thickness and radius..how much WORK consequently energy..does it take to meet the yield tensile strength of the steel?..
Anyone?..
Regardless of how scary the pressure peaks..work must be done to overcome the “surface” tension of the steel bubble

[JAParticipant @ja]

8 kJ is not a lot of energy, my kettle switched on for 4 seconds.

Once the container starts to yield, become plastic, it will absorb far more energy than when elastic. If one really wants to design such a container plasticity should be considered.

JA

[SillyOldDufferModerator @sillyoldduffer]

Coin crushing is an interesting application of this technology.

Going back to Joe's original question: if his pressure pulse is completely contained then the container will have to immensely strong. And even if the container doesn't break it's possible that a shock wave will travel through the wall and cause it to spall.

For personal safety it would be prudent to box the inner container leaving an air-gap of several cm between the two containers. The outer box is a screen rather than a pressure vessel and it doesn't have to be strong because the energy level is relatively low. But I have no idea how hefty the inner container would need to be.

An ordinary glass bottle will resist enormous pressures provided the pressure is applied slowly. But it is easily shattered by an impact. The elasticity of the material must be important but the analysis is well beyond me. It feels like a job for an expert.

I suggest the best way forward is to experiment. I would start with the biggest container I could make on my lathe. Cast iron is too brittle. Aluminium, brass and copper are too soft. I guess high tensile steel would be better than mild.

Good luck,

Dave

[Ian S CParticipant @iansc]

There were some experiments conducted, and written up in "Model Engineer" of the effect of pressure on a number of containers, including a thin walled throw away gas cylinder, and the effect of heating on a stove of a copper ball cock ball that had leaked, and what happened when the water flashed to steam, and the soldered joint parted, one half heading to the ceiling, the other getting squashed into the stove top.

Ian S C

[Anonymous]

Posted by Joe Page 1 on 23/11/2015 23:03:45:

Andrew – you caught me, I wondered if anyone would question these numbers. esr and resistance is about 0.1 ohm total, so about 9kA, still a lot of current, but I am using electrolytic's, so quite high ESR's compared to film capacitors. I do have a bank of films that's 34kV, 300J, esr 0.4ohm so peak currents of 85kA, but that's in a different project.

Don't forget that the ESR of electrolytic capacitors is often specified at 100Hz. If you're lucky, and the capacitors are intended for switch-mode PSUs then an ESR may be quoted at 100kHz. But that's still a long way below the frequencies you're talking about. The resistance of the connections, and the wire iteself also need to be taken into account. Finally, you're unlikely to get all the energy out of the capacitors in a short pulse due to dielectric absorption.

Andrew

[Joe PageParticipant @joepage27051]

Hi all,

Suppose I will keep updating as I seem to have stirred some discussion here.

Andrew – I will have to take some measurements to see what the ESR actually is, I'm sure it's probably going to be nearer 0.5ohm overall as the datasheets are always best case scenario's. Total resistance is too low for my multimeter to measure, so is less than 0.1ohm. But I only have the ye olde oscilloscope so can't measure single pulse widths yet to determine current, esr, etc.. So for now it's just brute force and see what happens, but I will eventually get a digital scope.

Got the capacitor bank almost there, fired it at 5.5kJ to test the switching system. I could feel the shockwave hit the camera and even with moulded ear plugs it was incredibly loud. Will do something more scientific with it soon but here's a video; **LINK**

[Anonymous]

Joe: Pretty professional looking setup! Good to see the 'Marigolds' in use. As long as that's all you're using them for. Current measurement, especially high frequency AC and transient is a pain. I suspect your best bet is a current transformer along with the digital 'scope when it arrives.

Andrew

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