![[tornado box, swastika-shape panels w/fan at top]](/amateur/tornbox.gif)
SCIENCE FAIR NOTES: If you don't need the device to last forever, you could build this out of cardboard or "gatorfoam" instead of plexiglas. Use duct tape instead of glue, and use incense sticks to make "smoke" instead of a humidifier. The bottom panel should not be cardboard, since it's a fire hazard with incense, or humidifier mist will make it soggy after awhile. If you use opaque materials, then make a big hole in one of the side panels and tape clear plastic over it to form a window. The fan creates the tornado, and the mist or incense smoke makes it visible. Instead of using an ultrasonic humidifier, you can use burning incense sticks or cones, but supply a large dish or pan on the bottom so the burning incense cannot become a fire hazard! If desired, put a small (15W) light bulb at the rear of the chamber to light up the mist tornado, and paint the inside of the chamber black to give good contrast. Try using the "12-volt micro fan" from Radio Shack, part number 273-240, and run it from a 9V battery. However, if the slots in the side of your tornado box are too wide, you'll need a more powerful fan. R. Grummer suggests using dry ice, which can sometimes be had at no cost by asking your local grocery store.
Top view of the tornado box looks like this (if the square top panel is removed) :
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TOP VIEW ||
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The four panels
are positioned to
form four slots
at the corners
The four 14"x24" vertical panels are fastened to top and bottom
square plates 18" wide, but
are not fastened to each other. Gaps between the vertical panels form the
slots. With 18in square top and bottom plates, and 14in walls, the slots
are 1in across, and the square central chamber is 12in side. Air rushes
in through the narrow slots at the four corners, then swirls inwards to
form the
tornado, then exits through a hole in the top. A small fan was
installed in the
center of the top plate (with a hole cut for the fan.)
If one wall is made of clear plexiglas, then you can see inside. Or use wood, but cut a large viewing hole in one side and cover it with stretched plastic wrap. Paint the interior black to make the tornado easily visible. The entire device can be any size, keeping the scale of the slots about the same of course: with a 12" square inner chamber, the slots end up being about 1" across. The total height is up to you. My device was about 2ft. tall. If you make yours lots taller, you either need to use a fairly strong fan, or you need to make the width of the slots smaller.
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The top plate of the version I built was a flat panel with a 2" hole in the center, with a high speed 120volt AC 3" box fan screwed over the hole. Fan air direction was aimed out of the box of course. This type of fan is available at surplus electronics outlets, and I think Radio Shack carries one version.
In order that it stand up to many weeks of wetness, I made the bottom of mine from a heat-formed plexi sheet, formed into a shallow funnel shape in an oven, w/crude frame to hold the edge, and a piece of ABS pipe used temporarily to punch the "funnel" shape into the hot, soft sheet. A hole was cut at the bottom of the funnel shape, and the edge of the hole was glued to a short piece of ABS sewer pipe. A perforated plexi disk covers the funnel mouth and provides the flat surface that the tornado needs in order to form properly. The ABS pipe led down into an ultrasonic humidifier which provided the marker-mist and made the vortex visible.
