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

Luke Gardner lgardner at wwest.net
Wed Feb 16 10:33:16 CST 2011


Jim,
In marine engines that have wet exhaust, most factory set-ups add the water 
to the exhaust stream via "risers" that bolt to engine water cooled 
manifolds.  something goofy like this also happens inside the exhaust flow, 
but in this case the water will actually migrate against the conventional 
flow of exhaust and crawl back up the exhaust stream to the backside of the 
exhaust valve and dither there at low rpms.  marine manifolds generally exit 
up , and when the engine is shut down the water will pool in the sump of the 
manifold and begin doing what it does best oxidize everything it touches, 
worse yet this is raw water, meaning if you are not in a lake or river, it 
brings in salt and whatever else, leaving behind accumulating salt deposits 
for later reactivation.
solution to that problem is to install a "deresinator" downstream of, but as 
close to the riser as possible, it consists of  a circular plate about 1/2 
the diameter of the exhaust plumbing that is suspended by three dainty legs 
centering it in the exhaust flow.  Effectively at the cold end of the 
resonance chamber.
I suspect that if you place a three inch od restrictor plate centered on the 
end of your flare tube, attached with non restricting legs, and another 
couple inches of 5" pipe things would change dramatically.  I would surmise 
that the tube would heat more evenly, thus eliminating the cold/hot end 
situation.  I would restrict as far as possible without affecting flow to 
undesirable levels.
An added feature to this compliments where you are headed with the internal 
flare tube, as it will give you more evenly heated surface area to transfer 
heat to another medium, I assume water.
If you try , please give feedback as this is where I am traveling as well 
with a current prototype.

Luke

PS
how loud does it get?
Add a few more different ID tubes you'll get a sinister organ   HA HA HA!


----- Original Message ----- 
From: "jim mason" <jim at allpowerlabs.org>
To: "Discussion of biomass pyrolysis and gasification" 
<gasification at lists.bioenergylists.org>
Sent: Tuesday, February 15, 2011 11:11 PM
Subject: [Gasification] thermoacoutics, rijke tubes, sondhauss tubes, pulse 
jets-- how do we make them not work?


any ideas out there for how to make a pulse jet robustly not work?

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")

when run under high load, it howls rather loudly. if art, it would be
fabulous. if a genset, not so good.

darrel tonight explained that we have made a rijke or sondhauss tube.
or really, an unintentional pulse jet. read about them here.
http://en.wikipedia.org/wiki/Rijke_tube. scroll down 3/4 to see
sondhauss close bottom tube, exactly as we have.

this apparently can happen with any pipe of one or two open ends, with
a big temp difference between the ends. a great enough temp diff
between the ends alone will set up the standing wave. you can make
the effect more pronounced with heat exchange meshes inside that
augment the pulse in one direction, but not the other.

turns out the best place to site a mesh, or apply your heat source is
about 1/4 length of the tube. (at least with the two end open type)
hmmm, we put our always on silcone nitride igniter right about the 1/4
length point. didn't think of that one. no idea if it is enough heat
to be making a difference in the resonance though. we should try
turning it off and seeing if the resonance changes.

an important thing that makes them work is the push and pull against
atmosphere. this suggests that one way to "detune" the tube would be
to put holes in the sides around the top portion of the tube. make
the pulse hit atm at difference lengths, and thus scatter the wave,
like one does in a car muffler.

or, maybe a flare outward would work? but that seems to only help
impedence matching, and make the trombone louder.

we put criss-cross baffles down the tube tonight. that helped quite a
bit, but didn't solve it fully.  also made more higher pitched tones.

this pulsing is also likely why we have flame backing up into the
mixing section/blower/etc in manners we never have before. i we did
most our testing on the blower and flame arrester, integrated
flare/exhaust with just the short stack. the big resonance problem
did not start until we put on the 4' extension.

i wonder if we could insulate our way out of this problem. insulate
the stack from bottom to top, even out the temp differentials so it
can generate less sharp thermal pulses.

any other ideas or experience for how to make your pulse jet not work
under any circumstance?

jim









--
------------------------------------------------------------------------------
Jim Mason
Website: http://www.whatiamupto.com
Current Projects:
- Gasifier Experimenters Kit (the GEK): http://www.gekgasifier.com
- Escape from Berkeley alt fuels vehicle race: www.escapefromberkeley.com
- ALL Power Labs on Twitter: http://twitter.com/allpowerlabs
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-- 
------------------------------------------------------------------------------
Jim Mason
Website: http://www.whatiamupto.com
Current Projects:
- Gasifier Experimenters Kit (the GEK): http://www.gekgasifier.com
- Escape from Berkeley alt fuels vehicle race: www.escapefromberkeley.com
- ALL Power Labs on Twitter: http://twitter.com/allpowerlabs
- Shipyard Announce list:
http://lists.spaceship.com/listinfo.cgi/icp-spaceship.com

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