T
Tim Williams
- Jan 1, 1970
- 0
Robert Latest said:BTW, a setup like this is really more like a relay, not a spark gap.
It's a relay that happens to spark a lot ;-)
Eh, not really, consider the whole thing is over in a hundred microseconds,
while a relay might take a whopping ten miliseconds to engage. For it to be
a "relay that sparks a lot" in any meaningful way, you would have to close
the gap before the sparks are done with.
Hum... figure it has to close the gap (sufficient to hold off the voltage
mind you!) in 10us or so. Let's say a mass 0.l kg, distance 0.02 m and time
= 10^-5 s. Average velocity must be 0.02/10^-5 = 2 x 10^-2 x 10^5 = 2000
m/s, breaking the sound barrier I believe! Assuming constant acceleration
from an initial velocity = 0 to final velocity = 4000 m/s, that's dv/dt =
4000 m/s / 10^-5 s = 4 x 10^3 x 10^5 m/s^2 = um, 0.4 gig m/s^2, or roughly
40 million G's? F = ma so that's around 4 MN (mega newtons), or for N = G *
1 kg ~= 10 on Earth, roughly 400k kg, that is to say, 400 metric tons,
sorry, tonnes. This force has to be applied with a rise time under say, 5
us, so inflating a wide piston with pressurized air isn't going to cut it
(speed of sound as it is). A light gas piston might, particularly if
pressurized greater, but it still begets fast risetime elsewhere to do it.
An ignited H2/O2 gas mixture might do it. Other propellants may also work,
considering the speed of sound is much faster with higher gas temperatures.
Oh, and a final kinetic energy of 1/2 * 0.1 kg * (4000 m/s)^2 = 800kJ
The force and energy would of course be much smaller given a lighter
contact, but that doesn't matter, your biggest concern (if it were a
concern) is really getting things to actually move in the first place.
Heh.
Fortunate that gasses can ionize so quickly and completely, huh?
Though on the other hand, if you pressurize or vacuum the spark gap chamber,
you can get shorter distances, requiring less robust drive train. 'Course,
if you pressurize the chamber, you can also get a lot more ions in the
spark! Come to think of it, that might be a good reason to use something
easily vaporized, like zinc or aluminum...
Tim