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<div class="moz-cite-prefix">Crispin,<br>
<br>
Please provide some photos (recent or historic) or links to
documents about the elongated holes.<br>
<br>
Paul<br>
<pre class="moz-signature" cols="72">Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: <a class="moz-txt-link-abbreviated" href="mailto:psanders@ilstu.edu">psanders@ilstu.edu</a>
Skype: paultlud Phone: +1-309-452-7072
Website: <a class="moz-txt-link-abbreviated" href="http://www.drtlud.com">www.drtlud.com</a></pre>
On 4/29/2014 6:26 PM, Crispin Pembert-Pigott wrote:<br>
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<p class="MsoPlainText">Dear Dave<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">That is a nice effort and well-reported.
Thanks for the small size pictures.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">In general, I feel you will get better
results and at less cost by using incoming secondary air to
achieve the effect. <o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">To get better penetration into the
rising column of gas, make holes as follows:<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Drill the size you want 1.5mm undersize,
maybe 2mm.<o:p></o:p></p>
<p class="MsoPlainText">Make/find a metal rod the diameter of
hole you want.<o:p></o:p></p>
<p class="MsoPlainText">Sharpen it enough to go into the drilled
hole.<o:p></o:p></p>
<p class="MsoPlainText">Place the sheet metal over a hole
drilled into a thick piece of steel - say, 10mm flat bar which
can reach inside the stove. The hole should be 3 or 4 mm
bigger than the sharpened rod.<o:p></o:p></p>
<p class="MsoPlainText">Punch the bar through the drilled hole
so the rod enters the centre of the hole in the thick bar.<o:p></o:p></p>
<p class="MsoPlainText">Withdraw it.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Now you have a hole with a radiused edge
and a small 'blurted' channel that will direct the air.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">If you really really really want to
optimise this, the outlet hole should be 1/3 of the area of
the inlet and the taper constant, and the length 6 times the
inlet diameter. This is hard to make. It has been known since
the 1880's. It applies to all fluids (air is a fluid). I used
it in Malawian tobacco barns and it tripled the effectiveness
of the 'educting effect' of the combustion gas energy in the
chimney. (It means using the chimney to pull air through the
barn like a fan would. The reason is higher energy, the effect
of the efficient gain in velocity, remembering that momentum
is ½mv<sup>2</sup>).<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">The blurted hole is far better at
getting air into a combustion chamber with velocity and
direction. The tools are home made. You may have to reduce the
hole size, it is so much more effective than a drilled,
sharp-edged hole. You can ‘point’ the hole by tilting the rod
as it is hammered through.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">For those with a technical bent, look up
the ‘elongation’ rating for the material you are using – say,
0.20. Calculate the final diameter of the outlet. Multiply the
diameter by (1-elongation) i.e. Ø*0.8. That is the smallest
hole you can start with to avoid splitting the end of the
material.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">For artisanal stoves, all secondary air
entry holes should be shaped in this manner. Full stop.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Regards</p>
<p class="MsoPlainText"><span style="color:black">Crispin
roaming<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText">The other night I started the charcoal
for our grill badly and we ended up with a feeble charcoal
fire for grilling chicken. I have a BioLite campstove and the
portable grill for it, so I started the BioLite and
transferred our chicken to it. We cooked the rest of our
dinner on American Sycamore twigs.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">The BioLite campstove, as you know,
forces air through the combustion chamber using an electric
blower. If you feed the fuel carefully, combustion occurs in
a spiral of red-orange flame, and scarcely any smoke is
produced.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">I'm not entirely sure how the spiral is
produced, but it looks to me like the forced air enters the
stainless "jacket" around the combustion chamber
circumferentially, circles the chamber, and enters the chamber
through the air ports with some momentum parallel to the
chamber sides.<o:p></o:p></p>
<p class="MsoPlainText">So it is the momentum of the air, not
the shape or arrangement of air ports, that produces the
spiral.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">I was inspired by the spiral of flame in
the BioLite campstove to try to create a spiral of flame in my
natural-draft TLUD that will help to complete the fuel/air
mixing and clean up the combustion. To induce the spiral, I
cut some sheet-metal strakes from 26-gauge mild steel and
installed them between the inner & outer cans of my can
stove.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">I have attached some photos of my stove
and strakes under construction.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">My first experiment with the straked
stove, using wood pellets as the fuel, produced a central
column of flame, blue at the bottom, yellow at the top, that
left soot on the stainless bowl of water that I topped the
chimney with. I noticed a few qualitative differences from
prior tests.<o:p></o:p></p>
<p class="MsoPlainText">The diameter of the flame was greater
than usual. The stove seemed to bring the water to a rolling
boil much faster than usual. The stove also made a hissing
sound, presumably because of increased turbulence.<o:p></o:p></p>
<p class="MsoPlainText">I don't remember hearing that sound from
this stove before.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">I ran a couple of experiments with
natural fuel (broken-up twigs) and one with less pellets than
the first. Each of the tests produced less flame than the
first, and I had to restart each of the natural-fuel burns at
least once. I think that I used too much wax paper to start
these tests, and the layer of char left by the paper blocked
the draft.<o:p></o:p></p>
<p class="MsoPlainText">There wasn't any hiss in any of these
experiments.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">I ran another experiment, tonight, using
the same amount of fuel as the other night (101 grams wood
pellets, the top layer of which consisted of pellets soaked in
91% isopropyl alcohol to aid starting), but with a couple of
changes to the stove. I removed the steel wire loop from the
chimney. I also removed the fan-shaped insert (shown in an
attached<o:p></o:p></p>
<p class="MsoPlainText">photo) from the bottom of the fuel
chamber. Conditions were also<o:p></o:p></p>
<p class="MsoPlainText">different: windy, with a rainstorm
starting during my test. This was a less vigorous burn than
the first one. I could not detect any hiss.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">If the strakes induce any swirl, it is
very subtle. Perhaps more strakes, or strakes at a different
angle will produce a more powerful effect. (My strakes rise
5.8 cm in 9.8 cm, measured around the outer can, diameter =
10.7 cm.) The dramatic burn in the first experiment may have
been due to windless conditions.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Dave<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">--<o:p></o:p></p>
<p class="MsoPlainText">David Young<o:p></o:p></p>
<p class="MsoPlainText"><a moz-do-not-send="true"
href="mailto:dyoung@pobox.com"><span
style="color:windowtext;text-decoration:none">dyoung@pobox.com</span></a>
Urbana, IL (217) 721-9981<o:p></o:p></p>
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