Re: [TCML] Rectifying a Tesla coil

["David Rieben" <drieben@xxxxxxxxxxx>]

Hi Tony,

Yes, I was aware that 14.7 lbs./ sq. in. was the maximum pressure
differential that could be obtained with an absolute vacuum. I was
NOT aware of how "hard" of a vacuum is drawn in a flourescent
tube from the factory, though. Two to three torrs is definitely quite
a significant vacuum and it would certianly have an insignificant
difference in pressure differential from an absolute (0 torr) vacuum.
However, I still feel that a flourescent tube would be excessively
fragile for the proposed rectifier tube use. I think we'll all experienced
just how easily these tubes can break with all but the most gentle han-
dling!

David

----- Original Message ----- 
From: <Sfxneon@xxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, August 31, 2008 11:56 PM
Subject: Re: [TCML] Rectifying a Tesla coil


> Hi David, all,
>
> Yes, a fluorescent tube would withstand even the deepest vacuum 
> obtainable.
>
> Look at it this way, the absolute pressure difference that can exist 
> between
> the inside of a vacuum tube and the atmospheric pressure  outside is no 
> more
> than about 14.7 pounds per square inch, and even less  above sea level.
>
> Normally, a fluorescent tube is backfilled to about 2 to 3 Torr of argon 
> (or
> other noble gas mix + Hg). Standard atmospheric pressure at sea  level =
> about 760 Torr, (which = about 14.7 PSI, or about 30" of  mercury column) 
> so, the
> pressure differential of a standard fluorescent tube is  only about .05 
> PSI
> less than one with a hard vacuum.
>
> It's a bit deceiving to think that the higher the degree of vacuum,  the
> greater the implosion force that would exist (since that is true with 
> pressure
> and ex-plosion forces), but that's not really so with a vacuum. It  can't 
> be any
> greater than the pressure outside the tube. Once you reach  the single 
> digit
> Torr range, there's not much real pressure difference  below that, so a 
> tube
> that will withstand a rough vacuum will most likely  withstand an 
> ultra-high
> vacuum too.
>
> It's really amazing how that 14.7 PSI adds up over a surface area, though.
> If I did the math right, a 4 foot tube would have over 200 square inches 
> of
> surface area, and at 14.7 PSI outside, the total force distributed over 
> the
> whole tube would exceed 3000 pounds! It's no wonder those things implode 
> with
> such a BANG!
>
> Tony Greer
> **************
>
> In a message dated 8/31/2008 10:33:33 P.M. Central Daylight Time,
> drieben@xxxxxxxxxxx writes:
>
> Hi Tony, Ben, all,
>
> I was also wondering if the ultra-thin walls  of a glass flourescent
> tube could withstand the pressure gradient of a high  vacuum with-
> out sustaining collapse (imploding)? Even if it could, it would  still
> prove extremely fragile!
>
> David
>
>
>
>
> **************It's only a deal if it's where you want to go. Find your 
> travel
> deal here.
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