Re: spark gap

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Jim,

Surface area is certainly important for cooling, but mass is also a 
major factor. A tube has little mass and as a result, transfers heat 
very quickly (heats up quickly, cools quickly). It also has the added 
surface area inside the tube for heat dissipation. A solid round 
stock will heat much slower and only has the outer surface to 
dissipate heat, but, the mass of the object has more "mass" to 
transfer within itself. This lowers the overall heat the object will 
need to dissipate and will require less cooling on the outer surface.

For our spark gap coils, we can certainly build gaps with tubes or 
solid stock and achieve stable running temperatures. In either case, 
it's a matter of just enough air to keep the gaps at a stable 
temperature, and in both cases, this can be achieved.

BTW, polished brass electrodes are very cool!  After I drill and tap 
a hole in the end of the solid round brass stock, I simply thread in 
a 2" long threaded stock and attach it to a high speed hand drill. 
Then place a wad of steel wool in my hand and spin the electrode in 
the steel wool. The result is a polished electrode.

Here's a pic. The image is old and the connection terminals have 
since been changed, but it does show the electrodes.
http://www.classictesla.com/temp/bba_brass_v2.jpg

The inside (white) tube which the electrodes are mounted to will 
slide out of the main gap tube attached to the fan. Thus, another set 
of electrodes can easily just be inserted (I ran across some larger 
solid brass stock on ebay for cheap and will probably make another 
insert). Haven't had the motivation yet to make the electrodes. I 
don't have machining tools, so everything I do is always with a vice 
and a hand drill. The baffle on the front is just another simple 
gizmo which directs airflow across only the electrodes.

Take care,
Bart


Tesla list wrote:

> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>
> When it comes to heat transfer (which is what you're doing here), 
> surface area is the thing.  The tube has area on both the inside and 
> the outside through which air can flow to carry the heat away.
>
> Increased mass may keep it cooler for a time, but it's like a big 
> capacitor, it just delays the inevitable.