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Thermoelectric Cannon Construction

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LAN_403

FastMHz

Fri Sept 15 2006, 06:05PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Hi all; I have an idea for a new type of electric gun that does not involve electromagnetics

. I did an experiment yesterday to confirm that it would work. What I did was I put the output of my 3.5kj cap bank into a bowl of plain water and fired the SCR...and sure enough, it violently converted to steam...so I took my thermoelectric cannon and put some water in it and started attempting to fire it at higher and higher voltages...200v - 800v nothing happened, but when I fired at 1000v, the whole PVC cannon EXPLODED into SHRAPNEL...apparently I had too much water in there and too small of an exit hole. But this means the idea should work, I should be able to use the electricity to instantly boil some water into steam and fire a projectile.

Has anyone done anything like this? My trouble now is figuring out how to build it so that the electrodes are always in contact with the water no matter what angle you aim it, and figuring out how much water to use vs empty space in the "combustion" chamber.

Psyko

Fri Sept 15 2006, 06:34PM

Registered Member #81 Joined: Thu Feb 09 2006, 11:57AM
Location: Paris, France
Posts: 43

That's a known device, called an etc gun, for electro thermo chemical gun.

FastMHz

Fri Sept 15 2006, 07:35PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

I knew there had to be a name for this...I googled and found Barros tried one but his is different - he is apparently using acetone as seen in his pics. I suppose that differentiates an ETC and an ET gun...I found no other hobbyists doing this...

I'm going to start by using spark plugs like he did and see what happens...but I'm sticking with plain water. Eventually I will do a similar thing as with my EM Rockets and find a way to use the pressure to launch a "rocket" like projectile.

Madgyver

Fri Sept 15 2006, 10:35PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Has been done before.

Fusion

Sat Sept 16 2006, 03:43PM

Registered Member #354 Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55

When a very powerful spark plug discharga at water, the water "atomize", and go to gas without boiling

After the discharge no heating or increase os pressure exist.

AndrewM

Sun Sept 17 2006, 01:15AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

Sam's analysis is simplistic and incomplete. He alludes to some mystery shockwave effect, when in reality, his test was bad, and his conlusions flawed.

The atomization is due to the shock from expanding gas in the arc path. This is genuinely non-magical boiling water, and the rapid expansion blows up the surrounding water before it has a chance to heat up. Once the arc ends, the small portion of water that boiled is rapidly cooled by the rest of the water (now scattered all over the place), and little change in temperature, and no change in pressure is observed.

Sam couldn't see this since he has a comparitively huge volume of gas inside the calorimeter, and didn't have a high speed high resolution pressure monitoring system.

Self Defenestrate

Sun Sept 17 2006, 03:05AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I used to have a little tiny cannon that I made out of an inch long peice of 1/4" copper tubing. It consisted of a 2 pin header epoxyed in one end, and connected to a camera flash unit with a few extra flash caps. To fire, it was loaded with a tiny hair of magnesium wool from a flash bulb and a wad of wet paper towel, wet enough to submerse the wool. When the bridge wire exploded, it would heat the water to a boil, and shoot that wad out fast! Sometimes fast enough to shred the poor little thing to bits. I couldn't get it to work with just water, so i think the magnesium might have alot more to do with my cannon than the water actually did.

Now, the way you could position the electrodes would be to use a metal barrel as an electrode, and a center rod as another. That keeps the water consistently in contact. I also think that any air in the so called combustion chamber is a waste, its just more stuff you have to pressurize.

FastMHz

Mon Sept 18 2006, 05:48PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

I don't think you had enough voltage in your small cannon to fire with just water...I was feeding 800v into mine with no results.. and then at 1000v and with pure water (no salt, etc), it blew up. As posts have said above, it's been done before, but I have yet to see an electrothermal cannon that uses just water; they all seem to use a filament or chemical of some sort. The secret to pure water is high voltage, enough that the relatively high resistance of plain water is no barrier.

Quantum Singularity

Tue Sept 19 2006, 01:23AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I had heard/read about the watergun before getting my first HV pulse caps many years ago and once I got them, that was one of the things I wanted to do. Thanks for the link madgyver... I was looking for it bu couldnt find it. As it says in the link, the watergun blew out sparkplugs that were threaded through 3/4" of steel so I figured i would really have to fabricate something prety well designed to hold up, and needless to say I never did persue that any further.

I really dont know much about the physics behind the water gun, I thought that the force was due to the high amount of current breaking apart the H2 and O atoms and the resulting explosion from pure hydrogen fueled by pure oxygen. If that is completely untrue please say so I can file that info in my heads recycling bin.

BTW, there was a mention of 'only water' being used in this short excerpt:

They manage to perforate a 1/4" aluminum plate with nothing
but the water fired from the end of the gun. They attempt to look
for anomalous energy production, but their results are inconclusive.

This type of electric gun seems prety rare but might have potential. Please FastMHZ, if you do further testing report back some of your results and findings!

FastMHz

Tue Sept 19 2006, 04:29PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Well I did some testing...blew a spark plug apart but did have successful water jets...it takes at least 800v through a spark plug to make the water "explode". I'll have to work on the gun some more and try firing a projectile outdoors when I get a chance.

I wonder if some of those huge aircraft engines might have larger, more durable plugs....anyone?

I wonder why there haven't been many of hobbiests trying this?

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