Re: spark gap question...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Jim,

On 2 Jul 01, at 13:54, Tesla list wrote:

> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> Supersonic flow is certainly possible in a spark gap, without even working
> hard. A 1/8" orifice driven from ordinary shop air at 60-80 psi will form
> visible Mach diamonds; especially if the compressed air is humid, or you
> look at the shadow of the air stream in strong sunlight (so you can see the
> density discontinuities).  1/8" is 8.5E-5 square feet, and at 1000 ft/sec
> (sonic speed, roughly), you're looking at around 5 CFM. The effective
> orifice size is going to be different, and the fine detail of the orifice
> has a huge effect (it changes what the shock waves look like.
> 
> 
> 
> However, before you start calculating madly, you should be aware that
> trying to actual calculate the flows and speeds is quite complex,
> particularly when you throw in the effects of the plasma, which radically
> changes the density, temperature, and compressibility of the gas.
> Supersonic nozzle flow is tough enough to calculate by itself.  This is an
> area where empiricism (i.e. try it and see how it works) might be a better
> approach.
> 
> And for the second part of the question, yes, the supersonic flow will blow
> the spark out. This is used in air blast circuit breakers, as well as a
> variety of other schemes, where the hot gas formed by the spark is used to
> blow the spark out (as in an expulsion type fuse).  It's also been used in
> high speed wind tunnels, where an ionized gas line is created across the
> air flow( using a row of spark gaps), which then drifts downwind at the air
> speed, allowing visualization of the air flow.

I don't think there is any dispute that a sufficiently powerful jet 
of air can blow a spark out. The question pertinent to TCs is "at 
what loss?". I've done it - and blown the arc into a four inch arc'd 
flame in order to obtain a first notch quench with a static gap set 
to its normal firing spacing. Marc's idea though is making use of the 
fact that the gap setting is far wider than that. It would be very 
interesting to see whether the TC system at work would work with the 
same scheme (wide gap spacing and no airflow at all where currently I 
have to use a finely adjusted air jet).

Regards,
malcolm
<snip>