Fire Tornado Rig
Fire. Scourge of Prometheus. Toaster of marshmallows.
It's time to make the elements bow in obeisance to the will of the hacker.
This rig is all about static airflow. It's a giant box, open on both ends, with strategically placed air intakes on each face of the box.
A contained flame source, in this instance, jellied alcohol, is placed in the center. As the heat rises, air is drawn in through the slits in each face of the box, and each inflow region is deflected by the path of the next face, causing the incoming air to rotate.
As this rotation is drawn into the flame, the speed of the rotation increases due to conservation of angular momentum, and a vortex forms in the center.
This rig needed some tweaking, to ensure that the area of the updraft was narrowed down, to prevent air from flowing down from the top of the box, and breaking up the vortex.
After version 1 was successfully tested, we at UAS decided to go big, or go home. We discussed several models for new rigs, some of which are still options, but the simplest method involved a rotating screen around a flame.
You can attempt to rotate a flimsy screen at high speed, or build an entire rig that rotates, based on a "lazy susan." When you're intentionally playing with fire, it helps not to burn yourself.
Remember: If you build a man a fire, he will be warm for a night. If you set a man on fire, he will be warm for the rest of his life.
We built a not-so-level, and not-so-square 2x4 frame for the lazy susan. (UAS needs a framing square and straight-edge BADLY!) But, it's a prototype....
On top of that, we mounted the circular wooden turntable, and a piece of drywall to limit combustion to the areas that we wanted. Then affixed a cheap pie plate to the top to hold the fuel source.
Our first screen roll was a thin gauge aluminum window screen, flimsy, and just tacked into place. When it lost its shape, and encountered the vortex, the screen started to melt. Also, the flinging around of the turntable by hand was less than optimal.
Necessity is the mother of invention. Pyromania is the bastard red-headed stepchild who melts your toys.
First order of business was to re-engineer the screen, with a roll of chicken wire as the solid core of the cage, far sturdier, followed with a outer layer of the aluminum window screen, carefully and meticulously sewn together with wire.
Next was a far more energetic fuel source - its effectiveness is up for debate.
Finally, the turntable was motorized. C-P will add the details of the motor rig here:
So, alpha runs 1, 2, and 3 were both surprising and enlightening.
alpha 1 - we actually accomplished tiny multiple-vortexes with a scaled-down model... interesting potential.
alpha 2 - really dialed in on it, and hit a great fire vortex.
alpha 3 - we scaled up to two fans high, and it kinda sucked.
Beta 1 - dry ice. No updraft, no vortex. we need some heat.
So, I went back to the drawing board, literally.
(Yes, I know it's a little uneven, what do you want for limited resources and time.)
So, the question becomes, how best to build it? (As something that won't melt, nor conduct heat to areas that will.)
In this version, we started using a larger fuel basin, as well as experimenting with different fuel mixtures.
With an internal diameter of 2 ft, and a 12 foot diameter circle for our 12 fans, we got some impressive results. Damn impressive.
2 small bottles of lighter fluid - 2 ft diameter funnel, approximately 20 ft high, for 1 minute, 30 seconds.
4 large bottles of LF - a 30-35' high full diameter funnel - 6 minutes.
9 bottles (various) - 40' high full funnel - 14 minutes. (Pan was off center) Very hard to ignite.
5 cans (small) - 25' - fans were off, moved in 6 inches from the line - 4 minutes.
2 cups of lf, 2 cups of alcohol (91%) - 20-25', but lasted almost 4 minutes. (Fans moved back to the line) Smaller diameter funnel - very compact.
3 cans of lf, 12 bottles of alcohol - 25-30', lasted 20 minutes.
Several new ideas came about as a part of the fire/fumes/alcohol during the UAS 1 year party:
- changing the basin shape/configuration to induce the shape of the vortex.
- a pressurized plenum, leading to a pipe with multiple holes. Same volume, smaller opening, higher speed and pressure. (Re-use the fans)
- experiments with fuel types, ratios.
Several downsides with version 3.5.
- Wind is still an issue, even very slight changes affect the vortex.
- Heat at a 6 ft radius was enough to melt the plastic on the fans.
- Galvanized coating on the basin started to melt, with potential health effects noticed.