[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [TCML] JAVATC - Question
bartb wrote:
Hi Jim,
Yes, a hyperbaric gap would have greater pressure and this will change
breakdown to some degree. As I understand the gap in question, it's not
hyperbaric. If it were a hyperbaric gap, then you would certainly want
to have the air flowing or at least the chamber pressurized equivalently
(assuming we knew a decent ball park pressure for a typical hyperbaric
gap).
One of the main points that Paschen showed was a curve identifying
breakdown voltage with gap distance or pressure. It's a curve because of
the molecular density of air and the probability of electrons getting
from point A to B.
Ahem... Paschen actually didn't take any data down low enough to get to
the minimum. His data fits pretty well on a straight line, and says
only that p*d = constant for a given voltage. I just got a copy of the
graphs from his paper, and I'll put them up in a day or two. (the
paper's already out there.. send me an email and I'll send you the link).
The curve shows that as the pressure is decreased,
breakdown voltage will drop (340V) and then will increase as pressure
continues to drop (one of the strange phenomenons of the density of
molecules in a low pressure environment. So what happens when we
increase pressure? Well, breakdown voltage increases (unless were below
that area of the curve described above).
In the "straight line" region (where Paschen actually worked), you're
looking at avalanche breakdown. But when the gap gets small or the
density gets low, (i.e. the mean free path starts to be comparable to
the gap), other factors come into play.
There's some well known data for small gaps where the breakdown does NOT
occur at the shortest distance.
In general, as the pressure is increased, the breakdown voltage should
increase and mainly due to the product of d x p (distance and pressure).
So if we double p, we should halve d for the same arc voltage. This is
one of my main points about hyperbaric gaps I've tried to mention in the
past regarding "cause of performance". Say we double the pressure and
leave the gap distance unchanged. Did we just double our arc voltage?
Probably not. You may have doubled the breakdown voltage, but not the
arc voltage, especially for mm length arcs, where the cathode drop is
the bulk of the voltage.
Yes we did. Is this being accounted for? I doubt it. I think were
currently just applying a mechanical air force into the gap and
observing the "performance". I'm not sure what the actual pressure
differential is, but I have a hunch that the performance increase is due
to the pressure causing the arc voltage to climb and thus the energy
release to be greater (and thus, a hyperbaric gap at 0.2" cannot be
compared to a blown gap at 0.2" with all else the same). If the pressure
was known, then we could increase the blown gap distance equivalently,
at which point, both gaps may perform similarly.
With the physics, it may be wise to identify and adjust the breakdown
voltage of hyperbaric gaps under pressure on the workbench before
running the TC (at least with an NST).
I agree
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla