[Stoves] Nozzles for TLUDs Re: venturi system -ratios of air and gas?

[Julien Winter]

Hi Paul, Frans and all;

When you talk of Kevin Adair's nozzle, are I assume you describing a
hourglass riser above the concentrator ring?  Something like the hourglass
comes to mind following Frans' comments on the coanda effect.  However, I
expect that the dominant force at the bottom of the hourglass would be
buoyancy, straight up.

A rough type of 'hourglass' venturi burner was invented by Dave Yarrow (ca.
2013) for barrel type TLUDs.  I built one myself, and it roars.  I have
attached a couple of photos

1) shows the whole unit.  There is a 130 L reactor barrel inside the 200 L
barrel, so secondary air was being preheated, and passed over the top of
the 130 L barrel where woodgas ignited under the concentrator.  The flame
then went up into the chimney burner.

2) shows the bottom of the chimney burner, which constricts to accelerate
the gases, then expands.  Where it expands, there are tertiary air holes
that are cut at an angle to get rotational turbulence (supposedly).  The
idea is to create a bit of a venturi suction for the tertiary air.

This unit is designed for a high gasification rate.  At low gasification
rates, the flame is below the concentrator.  I haven't done any more work
on this idea, because I have been focusing attention at on the initial
mixing of woodgas and secondary air.  I have yet to move upstream.

I don't have this unit any more.  I gave it to a friend who lives in the
countryside, and does not fear being shut down by the town's fire
department.



Of course, anything said about a natural draft, wood gas burner is
dependent on the supply rate of woodgas, because that can change its mode
of operation (as above).  The big problem for any burner is to get it to
work over a wide range of woodgas supply rates.  What works great at a
medium gasification rate, can be the cause of smoke at a high gasification
rate.

Premixing air and woodgas under natural draft would be a nice thing to
achieve.  The challenge under natural draft is to get the flow of the
mixture to be faster than the flame speed of H2, CO, CH4, so there is no
flash back.  We may be able to achieve that at higher gasification rates.
At low rates, the flame will likely flash back to the top of the char,
which may not be a bad thing for low turndown.

Cheers,
Julien.



-- 
Julien Winter
Cobourg, ON, CANADA
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