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<p>All,</p>
<p>There was a recent discussion on the biochar list about
turbulence in the mixing of wood gas and air for burning. Ron
Larson stated that this also belongs on the stoves discussion
list. The below and the attachment describe my disagreements
with turbulence for mixing in a TLUD and describes my hypothesis
for a better mixing system. It is the the same system used in
the 3 hour TLUD stove I described in an earlier contribution.<br>
</p>
<p>I had a very difficult time when I started working on the
Wonderwerk TLUD test stoves ~5 years ago. I realized how little
I knew about the processes going on inside the TLUD that make it
work. I wondered about pressures, temperatures, velocities, and
mixing and tried to learn what I could. No papers that I found
covered what I felt I needed to improve the stove designs. I
began to look into what makes a stove do what it does. First I
attempted to figure out why the flame goes up through the
stove. This landed me on buoyancy. My high school physics
taught me that buoyancy had to do with a boat in water. That
had to be extended to understand how buoyancy works in a TLUD,
or any wood or gas stove. I developed theories which changed
and improved over time, and are still changing. Buoyancy lowers
the pressure inside the stove to below atmospheric air
pressure. That is what brings the primary and secondary air
into the stove, the air follows the pressure gradient from
higher pressure outside to lower pressure inside. Once I
accepted that buoyancy was moving the gasses I began realizing
that the moving gasses had an effect on the pressure variations
in the stove through such things as the Venturi effect, back
pressure up stream of a restriction in the flow path, and
directional impact pressure. Then ideas began presenting
themselves as to how these pressure variations could be used to
improve mixing. This lead me to notice a mixing technique in
the Peco Pe and Champion TLUDs. At the upper edge of the fuel
chamber the wood gas meets the secondary air. The full <u><b>pressure
difference</b></u> between the outside atmospheric air and
the lower buoyancy provided gas pressure inside the stove was
pushing the gasses together. Since gasses are permeable, they
could merge, and the mixing here is excellent, molecule to
molecule. The flame is smooth, laminar, without turbulence, and
yet it was a good mix. However it looked to me that this mixing
was not optimized since the air could not reach the gas at the
center of the gas column. I set about to design a burner which
would optimize this mixing system. That is how I arrived at a
mixing system that does not use turbulence. I tried a number of
designs, including the Wonderwerk stove that was tested at
Lawrence Berkley National Lab, which was quite clean at moderate
power levels. No design seemed to solve all the problems. I
wanted it to be simple and cheap to build, and to be able to
turn the power level up without the burn getting dirty. I was
assisting Dean Still at Aprovecho with a different experimental
design, and after I left to come home, Dean continued his
experiments. He found a way of cleaning up the flame without
making the burner complex. He told me about it, and I thought
through it. I realized that his design fit the pressure
theories that I was developing. I adapted his idea to the
TLUD-ND stove and it seems to work. It is simple, and the power
level can be turned up quite high before it begins smoking. In
fact it can tolerate some forced primary air increasing the
power level very high. It can also be turned down to a stable
low flame. See the attachment for a description of this mixing
technique.</p>
<p>Respectfully,</p>
<p>Kirk H.<br>
</p>
<div class="moz-cite-prefix">On 12/27/2020 8:54 PM, Norm Baker
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAEZw-BBU0C+nFMOsqry-CsRUyU0SLCNDmA2Uj8LUF0u=XT0VOw@mail.gmail.com">
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charset=UTF-8">
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<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small">Kirk;</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small">I
cannot imagine how your stove does not need turbulence for
complete combustion. </div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small">The
simple fact that the flames are exiting the top indicates at
least some turbulence and there </div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small">has to
be turbulence just to mix the woodgas or pyrogas with
oxygen.</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small">Please
explain. Very interested.</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small">Norm</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:tahoma,sans-serif;font-size:small">PS
How's my cat doing???</div>
</div>
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