Open-Air Tornado Simulation

Instructional video for a 2ft tall chamber	Demo video of a 3ft tall chamber

Overall picture of the chamber. This is a pressurized plenum-type chamber, similar to the one shown in the Tornado Video Classics video series. The main difference is that this one has the plenum in the base and has an off-board smoke source (ultrasonic mist humidifier). Air is forced into the plenum base by the muffin fan. It then flows up through the PVC pipes. The pipes are capped at the top.Holes are drilled in the pipes every 4 inches in a line. These holes are aimed by twisting the pipes, so that they will generate a cyclonic airflow. The top fan creates the main updraft and keeps the vortex going.

Total cost (excluding fan and humidifier) is about $75.

The top panel of the chamber showing the fan, lights, threaded PVC caps and control box. CLICK IMAGE FOR DETAILS.	Underside of the top panel, showing the fan and PVC pipe anchors. The anchors are threaded pipe couplers. They are secured to the panel by the threaded pipe caps shown in the previous image.
I used a 115 VAC 20W industrial vent fan. This fan was small enough, but yet still has the power to draw air up the 3-ft height of the chamber.	The base of the chamber, showing the pressurized plenum, PVC pipe anchors, and muffin fan. I used a regular 12 VDC muffin fan, similar to those used as case fans in PC's. There's a variable voltage transformer controlling it, so I can vary the speed of the fan. CLICK IMAGE FOR DETAILS.
The backside of the chamber base, showing the tube that feeds the mist "smoke". Note that the PVC pipe anchors are attached the same way as on the top panel, only there's a 1/2 hole drilled through each one, to let the air through. CLICK IMAGE FOR DETAILS.	The Ultrasonic mist humidifier. This produces hours of "smoke" that's harmless to breathe (it might even help with a head cold!) They cost about $40 and are available at many drug stores. The tube fits right in the output.
Most humidifiers have a fan that pumps the mist out. If left alone, the mist will shoot out of the tube, disrupting the vortex. I used a scrap CD and some quarters to spread out the mist. You could also try to partially block the fan on the humidifier with some tape.	The vortex. The two rear black panels help with contrast, but also help block room air currents that might disrupt the vortex.