Flaming tube of death

(No actual death.)

I suggested a Ruben’s tube for a science fair project. It has everything needed to be cool – loud noise, the potential for serious injury, lots of instructions online and youtube videos of people not actually hurt by building one, and even an actual scientific principle or two to discuss.

(To be honest, the think of a hypothesis, plan an experiment, write up your results waterfall model for most science fair projects is completely bogus. The real hypothesis here was can we build something cool and seemingly dangerous over a weekend and get credit and the result was yes.)

We went to Home depot and found a variety of tube options. HVAC duct. Double-walled exhaust duct. Electrical conduit. The winner was 6′ steel fence post. A little hard to drill through, but not super heat conductive.

We only broke one bit on the holes.

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We went for brass-and-copper connections instead of quick-connect plastic, figuring that they wouldn’t melt and might look really cool.

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The ends were sealed with rubber from 3′ balloons, and the speakers were on clearance at Parts Express.

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First test. Big fun!

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Oops. See the bonus flames at the brass inlets?

problem

I couldn’t see these from the other side, but the camera caught them nicely. Eventually I noticed the scorch marks. I was intending to tap the holes for the brass, but didn’t have a tap of the right size, so we cowboyed it with duct tape.

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The metal connections turned out to just be leaky and tedious. After we switched to plastic, judicious use of teflon and silicone tape, and securing the speaker tightly with a hose ring, things started working predictably.

I learned that propane isn’t that scary to work with. It’s actually not easy to keep small leaks ignited in a well-ventilated environment.

Even a little wind interfered with the flames, and after trying various positions outside we moved inside (with due trepidation and discussion of safety).

Here’s a nice Rubenesque picture of standing waves:

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A frequency sweep:

Obligatory music:

It was great fun… highly recommended.

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