<html><head></head><body><div style="color:#000; background-color:#fff; font-family:verdana, helvetica, sans-serif;font-size:13px"><div id="yui_3_16_0_ym19_1_1521756600094_10264">Paul,</div><div id="yui_3_16_0_ym19_1_1521756600094_10270"><br></div><div id="yui_3_16_0_ym19_1_1521756600094_10389">I am unconvinced. One of the comments (the first - Arthur Noll) provides an explanation - it is the air being drawn into the base (primary air inlets) that stimulate the burning at the bottom.</div><div id="yui_3_16_0_ym19_1_1521756600094_10542"><br></div><div id="yui_3_16_0_ym19_1_1521756600094_10543">Hugh<br></div><div id="yui_3_16_0_ym19_1_1521756600094_10513"><br></div><div id="yui_3_16_0_ym19_1_1521756600094_10514">Noll's comment is copied below:<br></div><div id="yui_3_16_0_ym19_1_1521756600094_10390"><br></div><div dir="ltr" id="yui_3_16_0_ym19_1_1521756600094_10503">That is interesting, but I'm not convinced that pyrolysis products are
coming out of the bottom. You don't see any smoke coming out the bottom
until you put the flaming stick in there. The stick could be producing
the smoke that hits the bottom of the can, turns sideways and joins the
flow of air, much of which is rising up the sides between the
containers, while smaller amounts are going in to the wood. If it were
correct that products of pyrolysis were going down and then up, I
would expect to see a significant amount of smoke coming out the bottom
and up the sides all the time, not just when the stick was put in. And I
would expect to see soot and tar precipitating out on the surfaces
between the containers. Pyrolysis produces a combination of gases,
smoke, soot and tar. It is messy. I have built these stoves and this
area is always clean, even after many burns, just like what you have is
clean. I have always felt that the smoke, tar and gas from the
pyrolosis was rising up, and the preheated air coming out the secondary
air holes, going into this mixture of flammable gas and vapor, made the
jets of flame. I don't think it makes any difference whether you have a
jet of air going into a mass of flammable gas or if you have a jet of
flammable gas going into a mass of air, both can give you a jet of
flame.
</div><div id="yui_3_16_0_ym19_1_1521756600094_10580"><span></span></div> <div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: verdana, helvetica, sans-serif; font-size: 13px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"><font size="2" face="Arial"> On Thursday, March 22, 2018 9:05 AM, Paul Anderson <psanders@ilstu.edu> wrote:<br></font></div> <br><br> <div class="y_msg_container"><div id="yiv9198720191">
<div>
<div class="yiv9198720191MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal;" align="center"><b style=""><span style="font-size:14.0pt;color:black;">Explanation of downdraft in the fuel chamber of
TLUD (UP draft)
stoves.</span></b></div>
<div class="yiv9198720191MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal;" align="center"><span style="font-size:12.0pt;color:black;">Paul S. Anderson, PhD<span style=""> </span>21 March 2018</span></div>
<div class="yiv9198720191MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;line-height:normal;"><b style=""><span style="font-size:14.0pt;color:black;"></span></b><span style="color:black;">Stovers,<span style=""> </span>Previously
I wrote:<br>
*******************<br>
This link takes you to [what I am calling Video A.)<br>
</span><a rel="nofollow" target="_blank" href="https://www.youtube.com/watch?annotation_id=annotation_1962734105&feature=iv&src_vid=wzN-cYR84_Y&v=b0vM9aD78XY"><span style="color:blue;">https://www.youtube.com/watch?annotation_id=annotation_1962734105&feature=iv&src_vid=wzN-cYR84_Y&v=b0vM9aD78XY</span></a><span style="color:black;"><br>
Same fellow. and showing clearly UPdraft. Side by side
comparisons. Well worth watching. <br>
That is dated 2015. I hope that somebody will delve into this
further.</span></div>
<div class="yiv9198720191MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;line-height:normal;"><span style="color:black;">*****************************</span></div>
<div class="yiv9198720191MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;line-height:normal;"><span style="color:black;"> First, we all should thank Heath Putnam for his
research and for
reporting it publicly. He also provided an earlier video that
lh
cheng saw and called to our attention:<br style="">
</span><a rel="nofollow" target="_blank" href="https://www.youtube.com/watch?v=wzN-cYR84_Y"><span style="color:blue;">https://www.youtube.com/watch?v=wzN-cYR84_Y</span></a><span style="color:black;">
</span></div>
<div class="yiv9198720191MsoNormal" style="margin-bottom:12.0pt;line-height:normal;"><span style="color:black;">This
I
am calling Video B. Although dated earlier, it is better to
watch Video A
first.<br>
<br>
After sleeping on this question last night, I think I have an
explanation. And it also would explain what Nate Mulcahey
presented
as the "Everything Nice Stove" which he claimed was not a TLUD
stove
and claimed to be a downdraft flow of the pyrolytic gases (or
Opposite
draft). Putnam's work shows (but does not explain) the answers
about downdraft in updraft TLUD stoves. <br>
<br>
The big clue (revealed in video (A) above) is the difference
between the two
trial units. The difference is a sealed bottom that enables a
"co-mingled
air supply zone" for somewhat restricted primary and secondary
air versus
abundant secondary air that arrives separately from the supply
of primary
air. <br>
<br>
If the primary air entry is direct or very nearly direct and
sufficient even
with a small, restricted flow, it will sustain the migratory
pyrolytic front
(MPF), and all the air and gases will flow upward. This is the
CLASSIC description of TLUD operation.<br>
<br>
But consider the case of a TLUD-design stove that has a closed
bottom (or is
sitting reasonably tightly on a flat surface that prevents entry
of abundant
air) AND also has somewhat limited entry (via 4 holes in
Putnam's glass
outer cylinder) of air for <b><u>BOTH </u></b>primary and
secondary air into a
space (a "co-mingled air supply zone") from which BOTH types of
air
must be drawn. Therefore, the only exit is upward. The only
DRAFT
for the stove is powered by the flame of the burning gases at
the top.
<br>
<br>
Consider the case of a functioning TLUD stove when the MPF is
below a layer of
charcoal about 3 to 6 cm down from the top, with another 7 to 12
cm of raw fuel
below the MPF. The pyrolysis occurs, and the hot gases tend to
rise
upward through the layer of char and into the zone of the
cooking
flame. But the flame requires secondary air, which can only
come up
in the ring (annulus) between the two cylinders, and it does
come up.
This is the vast majority of the total supply of air (about 5
units for
secondary to 1 unit of primary air). In fact, that natural
draft by the
flame is pulling the air from the "co-mingled air supply zone"
(that
one place of air supply which is also feeding the primary
air).
There is therefore a reduction of air pressure below the MPF,
and that means
less movement of the primary air upwards. <br>
<br>
The result is that there is sufficient lower pressure that SOME
of the
pyrolytic gases move downward. Probably some swirling also, or
some
channels of gases going down but with SOME (at least some)
primary air (the O2
is the important part) moving to the MPF. <br>
With a little bit of time, some of the pyrolytic gases reach the
entry holes of
the primary air and leak outward into the "co-mingled air supply
zone" where there is fresh air entering and where those gases
can be
combusted (as shown in the Putnam demonstration in Video B).
Impressive. And if there is no flame down there, those
pyrolytic gases
can be pulled upward to become part of the upward flowing
secondary air THAT IS
NOW PRE-MIXED (-but rather diluted to some unknown amount
-) WITH
COMBUSTIBLE GASES. Nice trick, and you can see Putnam's
demonstration of a taller, stronger flame (Video A). This is
important. Pre-mixing is to be encouraged. But it
should be understood and done intentionally to attain consistent
results.
<br>
<br>
BUT in the described simple setup, production of the pyrolytic
gases is
suffering. There is a somewhat deficiency of primary air.
That could be forgiven (or overlooked or ignored) except for one
very important
factor:<br>
<br>
When the downdraft is occurring, the stove user loses some
control over the
fire. The draft from the burning gases is now regulating (in
part)
the operations of the TLUD stove. The normal control of a TLUD
fire is by
closing off some primary air, or using a small fan, but these
are no longer as
effective because of the co-mingled air. As the flame at the
top
changes when there is downward flow (shown by Putnam), there is
a ripple effect
to the air flows. Adjust, then adjust again, and then adjust
again. <br>
<br>
You can look at the Champion TLUD (only one hole for primary air
entry) or the
Quad or the Troika (by Awamu) with only one entry for primary
air, or some of
the other more established true TLUD stoves. The Peko Pe by
Wendelbo also keeps the two air sources separate.
Then look at Putnam's variation and at the Everything Nice stove
and see how
the primary and secondary air are comingled and subjected to the
draft created
at the top of the stove.<br>
<br>
Also consider what would happen if there actually was sufficient
downward draft
for the FULL reversal of the air flow in the fuel chamber. At
the
top there is flame. And how is there any O2 surviving in that
flame
so that it could go downward enough to go through the 3 to 6
(and deeper) layer
of hot charcoal in order for O2 to reach FROM ABOVE the top side
of the MPF and
to sustain that MPF for sending gases further downward? And
then those
pyrolytic gases would need to go out through what were the
primary air inlet holes,
and then be mixed with secondary air (but never catching fire
because somehow
there was not a spark there, even at the end of the batch with
red-glowing
coals????), and then rising in the annulus between the two
cylinders, and only
when entering the area of the main flame would those gases
combust. But this
supposition of FULL reversal of the air flow is impossible
because there are no
pyrolytic gases moving upward from the MPF. </span></div>
<div class="yiv9198720191MsoNormal" style="margin-bottom:12.0pt;line-height:normal;"><span style="color:black;">Conclusion:
In a TLUD stove, there can be PARTIAL downward drafting of the
created
pyrolytic gases when caused by natural draft of secondary air to
counteract the
flow of primary air. This is educational, but what is possible
is not
necessarily desirable or practical. <br>
-- <br>
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD<br>
Email: </span><a rel="nofollow" ymailto="mailto:psanders@ilstu.edu" target="_blank" href="mailto:psanders@ilstu.edu"><span style="color:blue;">psanders@ilstu.edu</span></a><u><span style="color:blue;"><span style=""> </span></span></u><span style="color:black;">Skype: paultlud
Phone: </span><a rel="nofollow" href=""><span style="color:blue;">+1-309-452-7072</span></a><u><span style="color:blue;"><span style=""> </span></span></u><span style="color:black;">Website: </span><a rel="nofollow" target="_blank" href="http://www.drtlud.com/"><span style="color:blue;">www.drtlud.com</span></a></div>
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