RE: Statistics & spark length and Air Pressure

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

In general, down to, say, a few torr, the breakdown field will be 
proportional to density.  Pressure and temperature both affect density 
(those of you familiar with "density altitude" and taking off in a small 
plane on a hot day understand this...)

A rough rule of thumb is that the pressure is halved for every 18,000 ft 
elevation.

Humidity has an (small) effect for two reasons: Water Vapor has a higher 
breakdown strength than Nitrogen; Water Vapor is less dense than Nitrogen 
(mol wt. 18 vs 28); the two effects counteract each other to a certain degree.



At 01:01 PM 6/10/2003 -0600, you wrote:
>Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><Gary.Lau-at-hp-dot-com>
>
>While the dielectric constant of air does vary somewhat with pressure, I 
>don't think this is pertinent to breakdown voltage vs. length.
>
>Terry posted a graph of static gap breakdown voltage with correction 
>factors for air temperature and pressure.  Temperature had only a minor 
>effect, but pressure was significant.
>See http://hot-streamer-dot-com/TeslaCoils/Misc/SGapVolt.jpg
>
>Consider how important low pressure is in plasma globes.
>
>Gary Lau
>MA, USA
>
>
> >Original poster: "by way of Terry Fritz 
> <teslalist-at-qwest-dot-net>" ><dhmccauley-at-spacecatlighting-dot-com>
> >
> >The dielectric of air varies (increases) with increased air pressure.
> >However, I am thinking this characteristic would mostly apply only to
> >pre-breakout conditions.
> >I think once that the air is sufficently ionized by previous streamers, that
> >spark length vs. altitude would somewhat normalize and that air pressure
> >would be less of a factor.
> >
> >Any thoughts?
> >
> >The Captain