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Re: Aerodynamics
Subject:
Re: Aerodynamics
Date:
Mon, 31 Mar 1997 23:12:56 -0500 (EST)
From:
richard hull <rhull-at-richmond.infi-dot-net>
To:
Tesla List <tesla-at-pupman-dot-com>
At 10:25 PM 3/30/97 -0600, you wrote:
>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?
The ohmic loses in a 1" length of Tungsten rod 1/8" diameter are just
not
significant compared to those in a 1/2" rod of the same length. The
other
loses around the circuit of all types cause this differential to pale by
comparison.
R. Hull
>
>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.
The effect of the low pressure area trails very close to the rear of the
electrode and is very strong and pronounced. With a blade or vane at
any
range, the air flow produced by such a vane would probably not remain
strong
enough at range to conteract the negative pressure region hugging the
electrode itself.
R. Hull
>
>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.
You may be quenching good enough already! Try the vane idea and see.
If no
improvement, then the idea was a bust. R. Hull
>
>
>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
>>
>
>