Pipe pressure rating

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

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

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

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

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**

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