I was just watching a popular science program (“Bang Goes the Theory”, the BBC’s replacement for “Tomorrow’s Word”). It showed an experiment where a tornado was created by lighting a fire and spinning the air as it rose into a tube. The result was a massive fire tornado.
On wikipedia I’ve read about “Fire Whirls” which manage the same thing without the aid of a tube.
How could I get a similar effect with a candle, oil lamp or other small scale open flame?
I’ve seen these type in a fireplace showroom. But they do use the tube like you described.
Yeah, the program I mentioned pretty much had a giant one of those.
If air must approach the base of the flame on a path that is tangental to the flame, and especially along several such paths that are all tangential in the same sense (eg all paths want to skirt to the right of the flame), then it will spiral.
I have a childhood memory of a science demonstration with a pan of flammable liquid sitting on a turntable. The turntable was circular and about 1-2" thick. Secured to the edge of the turntable was a cylinder of hardware cloth or other heavy-duty screen material, about 16" in diameter and maybe 36" high. The liquid was lit and the turntable began to spin; how fast I don’t really remember. A fire vortex formed which extended quite a bit higher than the upper edge of the wire mesh cylinder. So a partial cylinder may be sufficient.
Like this demonstration, only with a larger pan and coarser screen.
So could this work, I’m going to try and;
[li]Take two (empty) 500ml drinks cans.[/li][li]Cut the top (the bit with the ring pull off of one.[/li][li]Slice the bottom (plus a couple of cms of the body) of the other.[/li][li]Flip the first can over, punch a hole in the middle of the (concave) base and another in the side.[/li][li]Place some sort of fuel delivery system in it (maybe a metal or glass tube full of petrol with a rag stuffed in the end).[/li][li]Slide the second can onto the top (now the base) of the first to make the entire thing airtight.[/li][li]Punch a couple of holes near the bottom to draw in air without interfering with the top.[/li][li]Light it (outside, preferably on some gravel or tarmac) and see what happens.[/li][/ol]
The idea is that the flame from the torch will flow from both A and B (but hopefully not the intakes) and the flow from B will cause the lateral air current to make a vortex of A.
Would this work? Is there anything I should change before I go ahead? What’s the best size for A and placement for B?
Don’t use petrol (gasoline). It is too explosive, and fumes can drift and ignite in places you didn’t intend. Use something like diesel fuel.
Are you sure? The whole point of the rag is to act as a wick that limits the amount of petrol, and the mechanism mainly relies on it’s volatile nature to make sure there’s a decent flow.
Don’t worry, I’ll be lighting it in the middle of an empty space and from a distance. I’ll even wear goggles.
Reel EFX in Hollywood does a nifty fire tornado. They used to have a bunch of videos on their site from the construction and testing phase that might help you out. They’ve moved everything around since I worked with them last, but I’ll bet you can find some good info there if you spend the time. Lots of other fun videos too.
I second Fear Itself in suggesting gasoline wouldn’t be a safe fuel. If you really know what you are doing, then have at it - but if you aren’t already an expert in burning gasoline in various ways, you should probably be pretty frightened of it.
Arguably gasoline is not explosive. What I think is the most useful definition of “explosive” when discussing a chemical is the criterion that ignition would be propagated by the pressure wave, and what gasoline vapor in the air does instead is catch fire very fast, which is a little different (though often still called an “explosion”). But it can get out of control amazingly quickly, and the sudden burst of heat and pressure (whatever you call it) has the very nasty ability to throw additional liquid gasoline around, and onto things, and make it evaporate very fast, and ignite in what seems like no time.
If you must, use gasoline, and when your universe spontaneously morphs into Hades, back time up a couple of seconds and call it quits right there.
'Course, that’s just my advice. My experience includes trying unsuccessfully a couple of times to get gasoline to ignite, and getting it to ignite in downright amazing fashion trying to start a camp stove which left me shaking for days, and watching garage workers toss their lit cigar butts into open pans of gasoline to extinguish them. I just don’t think the stuff lends itself to useful anticipation.
Well I only need a large flame to test my theory, so if anyone could suggest a safer fuel to use in the contraption I described above, it would be helpful.