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Re: Aerodynamics



Subject: 
        Re: Aerodynamics
  Date: 
        Sun, 30 Mar 1997 12:40:13 -0700 (MST)
  From: 
        Chip Atkinson <chip-at-pupman-dot-com>
    To: 
        tesla-at-pupman-dot-com


Interesting post, but I have a few questions that are no doubt a result
of
ignorance.

I understand that the main source of loss in the tank circuit is the
spark
gap.  Wouldn't putting in a small tungsten rod in place of larger
electrodes increase the resistance, and therefore the losses, or are the
losses non-ohmic (resistive), which consist mainly of heat, light, and
noise?

Another idea that comes to mind is to have some radial vanes much like a
centrifugal fan on the inside of the disk, away from the electrodes. 
The
purpose would be to provide an outward air flow which would help cool
the stationary electrodes and quench the spark.  It would also be
removed
from the proximity of the moving electrodes and thus reduce the eddying
around the electrodes themselves. Looking down on the vane and moving
electrodes we would have something that looks like:
----  . , where the ---- is the vane, and the . is the electrode.  

Ah, but enough of the armchair coiling.  It's time to rewire my power
cabinet....

BTW
I do have a 12" diameter wheel for my rotary, so the mods wouldn't be
too
bad for me though.


Chip

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
 Chip Atkinson 
 http://bhs.broo.k12.wv.us/homepage/chip/info.htm
 --- Tighten it 'till it strips and back off half a turn ---
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

On Sat, 29 Mar 1997, Tesla List wrote:

> Subject: 
>         Aerodynamics
>   Date: 
>         Sat, 29 Mar 1997 11:54:57 -0500 (EST)
>   From: 
>         richard hull <rhull-at-richmond.infi-dot-net>
>     To: 
>         tesla-at-pupman-dot-com
> 
> 
> All,
> 
> I have always held that rotary gaps of the simple type, as built by the
> majority of the Tesla community, often flame, flare, or exhibit "follow
> around" for several reasons.  The most obvious is poor design and lack of
> forethought in the tank circuit itself.  The other reason is Aerodynamic
> fluid flow problems!
> 
> We all want to seen the rotary as a big fan in addition to a spark gap.
> This fan cools the electrodes and keeps a steady flow of churning air at the
> stationary points. How many of us view the system as an series of
> instantaneous events?
> 
> If we invision the moving point as a slab sided cylinder in motion, the
> fluid flow dynamics will show a low pressure region extending well behind
> the point.  the faster the point moves the lower the pressure in the region
> and the more extended it becomes.  Furthermore, we all know that in air, at
> reduced pressures, the electric conduction is more readily supported due to
> reduced mean free path.  This remains the case until we get to below 1 or 2
> mm of pressure and then the situation reverses and the resistance of the arc
> goes up quickly due to reduced charge carriers.
> 
> Thus, as the points are firing and the gap tries to spearate, the low
> pressure region following in the wake of the moving cylinder electrode
> allows conduction to continue long after the points are beyond normal spark
> over.  All this seems to occur in the low pressure region.
> 
> The biggest flamer gaps I have seen have been high speed gaps with big
> electrodes!   Realizing what the cause might be, I have always used
> electrodes smaller than 1/4" and lately in magnifier work, have opted for
> .180 tungsten rod up to 12KW.  I also opt for a much slower gap or rotor
> speed and a larger wheel diameter.  I often operate at no more than 1800 rpm
> on a 1 foot rotor and use multiple gaps in series with the rotary and run
> lethal rotary gap spacings in the .010" range.  I never have experienced
> flare, flaming or "follow around" up to the maximum of 15 KW which I ran
> on Nemesis a few times.
> 
> We might do well to think about this problem a bit.  I am planning some
> aerodynamically designed electrodes in future.
> 
> Richard Hull, TCBOR
>