[Gasification] thermoacoutics, rijke tubes, sondhauss tubes, pulse jets-- how do we make them not work?

[jim mason]

> we're having lots of problems with thermoacoustics now that we've put
> a tall stack on our gasifier swirl burner.  we're using a tall stack
> now to keep startup gasses away from the operator.  the swirl burner
> is 5" in diameter, 10" tall. we've added a 4 foot or so stack of the
> same 5" diameter. it looks like this
> http://www.gekgasifier.com/forums/showthread.php?t=501 (though this
> one without the joint at 10")


completing the circle on this question from a few months ago, here's
what we finally found solved the problem- insulation.  we found that
if we simply insulated the stack from bottom to top, eliminating the
hot/cold delta, the thermoacoustic effect went away.   more reading in
the rilke / sondhaus tube effect clarified that it needs this temp
differential, and if you eliminate the temp differential, the effect
stops (which it did).

this was one of the many good suggestions offered here.  we didn't try
all of them.  but some of note.

1.  cut a V in the top of the stack like done to quiet some pulse jets
2.  drill holes towards the top, or other shapes to soften the
transition at the end to reduce the pulse wave
3.  put a floating "deresonator" plate in the tube
4.  angle the tube, or otherwise put angle plates in it to break up
the standing wave.
5.  drill a hole in the side down low and put a rod across the flame path.
6.  experiment with expansion chambers like a two stroke exhaust,
except with the intent of "detuning".



i don't know which of the suggested will work.  we ultimately decided
the easiest one was the insulation and tried that.  it worked, so we
stopped there for now.

as usual, thank you for the input.

and btw, what problem of physics do gasifiers not touch?

j