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Re: [TCML] High Power Static Gaps
Sfxneon@xxxxxxx wrote:
Questions and ramblings to the group:
Besides the advantage that a rotary has in setting the break rate and phase,
what else does a rotary do to make it more suitable for high power work? If
the main advantage is the cooling/deionazation provided by rapidly moving the
electrodes through the air, then it seems to make sense that moving the air
over the electrodes is much simpler and safer. The idea of a triggered static
gap intrigues me even more because the BPS rate can be changed, with just the
turn of a knob.
So far, I have only seen and used metals like copper and brass as the
electrodes in sucker or vortex gaps. Has anyone incorporated tungsten rod into the
design, maybe mounting a rod axially inside the hollow electrodes, letting it
protrude slightly out of the ends?
The high power blast gap designs I've seen didn't use a refractory metal
(e.g. tungsten) in the gap, presumably because it isn't needed. Enough
airflow keeps the part cool. In fact, one of the gaps shown by Fruengel
actually had the active part of the gap made of aluminum.
It looks like that should make a better
quenching gap, than one made of softer metals. Also, the mass and shape of the
electrodes versus heat dissipation would need to optimized. I'm not sure if
bigger is better here, since surface area/mass ratio plays a big part in
removing heat. Would it be easier to keep a small or a large electrode cool?
The typical gap has air/gas coming in or out through the center of the
electrode, which is flat faced (see, e.g.,
http://home.earthlink.net/~jimlux/hv/blastgap.htm
).
The gas actually heated by the spark is carried away rapidly (velocities
of 1000 ft/sec are possible), and the heat in the electrodes themselves
(either from radiation from the arc channel, or from IR heating) is
presumably carried away the same way.
Keeping the KISS principle in mind, how far can a single static gap be
pushed without exotic cooling methods,
Fruengel claims 50 kHz rep rate at 2Joules/discharge-> 100kW
using only the motor/turbine with some
applied aerodynamics and thermodynamics? There are literally millions of vacuum
cleaner and shop-vac motor/turbines out there already for cheap or free, and
these seem to be a good choice for both pressure and vacuum. The noise can be
almost silenced by putting it in a box with some internal baffles and lining
it with thick felt, fiberglass or other sound absorbing material. I used to
use these same vacuum motors to build vacuum pumps for player pianos, and once
the piano started playing, the motor could no longer be heard.
I think you're looking at substantially higher pressures and volumes.
several CFM at tens of psi, perhaps.
The drawings and descriptions I've seen talk about "choked flow" in the
gap, which generally means supersonic. (Getting supersonic flow in a
1/16" hole doesn't take all that much airflow)
At 50 psig, you're looking at about 4 scfm
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