Re: water arc expolsion- was: water as spark gap dielectric

["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>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, April 19, 2003 8:12 AM
Subject: Re: water arc expolsion- was: water as spark gap dielectric


 > Original poster: "S & J Young by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<youngs-at-konnections-dot-net>
 >
 > Hello coilers,
 >
 > David is right - submerged spark discharges are used for metal forming
 > because huge pressure waves result.  I have blown out the side of cans
with
 > underwater discharges from a 4 mfd 15KV capacitor bank.  About like a
cherry
 > bomb.

That's 450 Joules.. a far cry from the usual tesla coil primary bang size.
I don't see many TC designs using 4 uF primary caps..

 >
 > As I understand it, a lot more energy gets released in an underwater spark
 > than one through air.  The underwater gap has a lot more resistance and so
 > is able to absorb a lot more energy, and less gets wasted in the capacitor
 > and associated wiring.

Nope.. the energy is going to be the same (in a capacitive discharge
scenario, not in a closing switch scenario). The reason they do it in water
is that the water provides a incompressible mechanical transfer medium for
the energy in the spark to the workpiece.

To a first order, spark losses are proportional to length (by the time the
spark gets going, it's all a plasma.. whether surrounded in liquid or gas is
immaterial), and higher breakdown strength (in a V/m sense) means a shorter
spark.  Actually, in a water spark, the plasma density is somewhat higher
because the mass of the water inertially confines the spark, at first.
Higher plasma density ==> lower losses due to resistive effects.

   For this reason, I don't understand why one would
 > prefer water gaps for TCs.  We want our gaps to exhibit the lowest
possible
 > loss.