Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
Here's a demo of exploding wires
http://web.mit.edu/Edgerton/www/ExplodingWire.html
They use 500 uF @ 800V to zap a shortish piece of NiCr wire. With
their energies, I'm not sure they're really getting an honest
explosion (as in creating a shock wave).
In my experience, it takes about a kJ to get a good explosion from a
one meter long wire in the AWG 32 or finer area. Both aluminum and
copper wire work. I ran 5-20 uF at 10+kV.
Exploding wires is a matter of peak powers, too.
There is a definite series of qualitatively obvious phenomena. From
lowest to highest energy:
Melting
Melting into droplets with sparks (a "pop", like a fuse burning out)
Melting and flashing over like a spark(a crackle or "flash", like
any old spark, eg. from a TC)
Exploding (a distinct "bang" or "crack")
Visually, they're quite different. All of them, except the
explosion, appear to "propagate" along the wire, at least in a meter
long segment.
in order to explode, the wire has to liquefy, then vaporize, then
ionize, before the material has a chance to move around. So, you
have to put a fair amount of energy into the wire, fairly
quickly. You can calculate the amount of energy required to
vaporize the wire pretty easily by looking up the heat of fusion and
vaporization for the material.
The dyanmics are quite interesting, because the resistance of the
wire rises rapidly as it heats, so getting enough current into it
quickly enough requires a substantial voltage.
Thanks for all you do,
Jim Mora