The Ruben's Tube Experiments are done for today -- and we developed a few good ideas for improvements on the next tube (or set of tubes; we are building four!)
Robin and Debbie made it over for a short time right at six tonight, and I ran the tube through its paces (not unlike the video I took of it later, see the link at the end of this post). While they were here, Michelle showed up too, but then they all left at 6:30, leaving me with a tub of square, organic marshmallows to roast in the flickering flames.
Michelle had the idea, to help counter the way high-frequencies blow out the flames nearest the speaker, to move the speaker out into an extension that would act as a buffer and diffuser of the sound waves. We later did a wee test, closing the holes near the speaker, to see if having a longer dead zone helped. It did seem to slow down the blowout a bit, but in the case of a steady-state tone, they still blew out. But for varied music, it might help a little bit.
Just about when they left, Randy showed up and we got down to poking the tube in ernest.
The first thing I did was record a video using the laptop's built in camera of the tube as it stood: small holes (1/16 or so) drilled every 1/2 inch on a 4" diameter 6' long ventilation tube. The speaker is mounted on an 8" adapter on the left side, and the gas inlet is on a 6" adapter on the right side.
The first tests involved using a signal generator to feed very low frequency waves into the tube ... 4 to 10 Hz, more or less. These pulses of sound provide very interesting "dancing fire" effects. Higher frequencies make a more frenzied flame, and tend to blow it out near the speaker.
Then we ran all kinds of music through it: Blue Man Group, who are heavy on percussion and base; some Enigma; some this, some that (I forget now what we used). Dance music is best, providing dramatic flame effects. Voices and a lot of wimpy instrumental don't do much at all.
We also drilled 5/32" holes every inch (expanding existing small holes), to test larger holes. These lowered the pressure in the tube a bit, giving a large more diffuse flame (I thought) but were also less inclined to blow out.
We used metal tape to block off holes on the edges, but this didn't change the behavior much. Randy used metal tape to block every other large hole and all the small holes, which hurt the tube's ability to relight itself and didn't help the blowout problem.
Ideas for the next tube include Michelle's buffer; Randy though that putting the gas pressure where the speaker was might help. On that one, I'll attach the gas hose on the extension where the speaker goes, and possible a second branch at the far end. This will put the gas pressure and speaker pressure on the same side, and might help. If I attach quick-releases on both sides, this can be configurable.
The hole pattern that we left with seems to be a good one; tiny holes every inch, and quarter inch holes between them.
All in all, a good experiment. Too bad Matt and Susan and Silona were busy, we missed them! But I'll show M&S the tube tomorrow morning, briefly, before Dim Sum. Yummmm.
See the video here:
Posted by Edwin at March 3, 2007 10:17 PM