museum tornados, also electrostatic speculations

[William Beaty <billb@eskimo.com>]

On Mon, 28 Sep 1998, Clifford Bettis wrote:

> I am pleased to announce the birth of a new demo. We turned it on the
> first time this morning and it worked wonderfully. My thanks to Dave
> Maiullo whose vortex generator provided the inspiration. If I am asked,
> to whom should I give the credit for the original idea? Was it William
> Beatty?

Actually, the original was from World Book Encyclopedia from the late 50s:

(now on BIZARRE STUFF YOU CAN MAKE IN YOUR KITCHEN)
    http://freeweb.pdq.net/headstrong/hurr.htm

I vaguely recall seeing a paper from the 50s about this, so it probably
originated from mainstream meteorology or physics.

While at Museum of Sci. in Boston, Doug Smith and I built the ultrasonic
humidifier version as part of a set of activities to accompany the
Peitgen/Richter "Edge of Chaos" fractal art exhibit.  By turning the fan
speed up and down, the tornado would undergo a laminar-to-turbulent
transition.  It was basically a hall exhibit, with fan speed control
pushbuttons and a triggered timer which would run the mist for awhile if
any button was pressed. 

One thing I had always wanted to add to this exhibit: a thin plane of
scanned laser light.  Try waving a laser across the mist tornado with room
lights off. You'll see a brilliant "cross section" of the fluid flow.
(note:  it's much brighter if the laser light is directed TOWARDS the
observer, with proper safety considerations of course.)  A single, fast
sweep will "freeze" the pattern of turbulence even when the air velocity
is very high.

Another untried idea (would be fascinating if it works): voltage-dirven
electric tornado.  I never had the ambition to work with this.  Perhaps
somebody here would like to give it a try?

If a tray of water is placed in the bottom of the tornado machine with the
fan speed at maximum, a small hump develops at the location of the vortex
core.  If the air pressure was low enough, perhaps the water surface will
develop a point, and begin emitting a spray of droplets.  ("Waterspout"
tornados do this, as do dustdevils when they cross a pond.)

This water spray could act as an electromechanical drive for the tornado
if the spray was electrically charged, and if there was a large, vertical
e-field.  THe moving column of spray would entrain air and transport it
upwards, and new air would spiral in from the sides.  I get this idea from
Dr. Vonnegut, the "heretical" weather physicist.  Therefor, place a metal
screen horizontally over the water, and connect it to a high voltage power
supply ( connect the water tray to the opposite terminal of the supply. ) 
The water spray created by the tornado chamber will then have an opposite
charge induced on it, and the water droplets will be attracted upwards to
the screen and some charge will flow.  Work will be done upon the droplet
cloud.  With luck, we could then turn the fan off, and the tornado would
persist. It would be an electrostatic linear motor, the "rotor" being
composed of the upwardly-driven cloud of charged droplets.  Sort of like a
Vandegraff machine which is run as a motor, where the e-field drives the
motion of the belt instead of vice versa. 

To have a chance of success, the e-field must be large, so the gap between
the screen and the water should be fairly small.  Also, the power supply
would need to give significant energy flow, on the order of the watts of
work done by a small electric fan.  Something like tens of KV at several
milliamps, which suggests that a VDG machine would NOT work as a power
supply.  Instead try a neon-sign transformer and a HV diode.  This is a
safety hazard, so it's probably not such a great project for untrained
students.  On the other hand, I've never heard of anyone trying to build
such a device, so perhaps the age-old tornado demo might easily become
some basic research attainable by even a funding-challenged highschool
kid. 


((((((((((((((((((((( ( (  (   (    (O)    )   )  ) ) )))))))))))))))))))))
William J. Beaty                                  SCIENCE HOBBYIST website
billb@eskimo.com                                  www.eskimo.com/~billb
EE/programmer/sci-exhibits          science projects, tesla, weird science
Seattle, WA   206-781-3320          freenrg-L taoshum-L vortex-L webhead-L