<div dir="ltr">Dear Kirk and All,<div><br></div><div>Generally I think that the study of the TLUD has opened up new thinking about the Rocket. Super insulating the Rocket (and every other trick to improve time, temperature, turbulence) helps to keep only the tips of the sticks burning and to burn up quickly the made charcoal so the air flow under the sticks is not blocked. If we think of the air flowing under the sticks as 'primary' air and the air flowing on top of the sticks as 'secondary' air the intention is the same as in the TLUD. The primary air controls the rate of reaction (solid making gas) and the secondary air creates mixing. In the Rocket the flame naturally flows up the back wall and big open spaces occur near the front walls. Almost no mixing, unfortunately.</div><div><br></div><div>Using the primary air to slow the rate of wood gas production and forcing the secondary air to mix cleans up the Rocket as in the TLUD.</div><div><br></div><div>I'm hoping that Kirk and company will come to Stove Camp and figure out how to optimize natural draft mixing in the Rocket.</div><div><br></div><div>Best,</div><div><br></div><div>Dean</div><div><br><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Apr 26, 2015 at 1:07 AM, kgharris <span dir="ltr"><<a href="mailto:kgharris@sonic.net" target="_blank">kgharris@sonic.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div bgcolor="#ffffff">
<div>
<div><font size="2" face="Arial"></font></div><font size="2" face="Arial">
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt">Dean,</span><span style="FONT-FAMILY:'Times New Roman','serif';FONT-SIZE:14pt"><u></u><u></u><u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt"><u></u> <u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt">This
is a clever idea.<span> </span>The inner dark
radiating surface of the chamber liner would return heat to the flame
while it's outer shiny surface, being a less efficient radiator of heat,
would radiate less heat outward.<span>
</span>Below are some thoughts which I hope are not too far off base.
<u></u><u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt"><u></u> <u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt">My
first inclination is that your rocket stoves are so well insulated that it would
make very little difference since all that heat is being retained anyway.<span> </span>A re-radiating surface would be little
more effective than a reflective surface since they both do the same thing,
return the heat to the flame. However, if a radiant surface could radiate fast
enough to keep the wall temperature lower than it would be otherwise
(conservation of energy, if the surface is radiating heat then there is less
heat in the surface so the temperature is lower), then the stove could be
operated with cooler walls as well as a hotter flame. This would be helpful
by allowing less heat loss to the outside and by keeping the wall cooler for
better lifespan. <span> </span>A hotter flame
would not be more efficient unless there is enough preheated air, mixing, and
dwell time to take advantage of the extra heat.<span> </span>Back to the basics required for a
fire;</span><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt"> fuel,
oxygen, and heat.<span> </span>If there is not
enough air then increasing the heat won’t help.</span><span style="FONT-FAMILY:'Times New Roman','serif';FONT-SIZE:14pt"><u></u><u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt"><u></u> <u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt">If
I were working on improving the efficiency of the natural draft rocket stove, I
would want to first design an experiment that would tell me what the gas flow is
inside the stove. Where is any excess air, flame and any unburned wood gas, how
are they moving, and how much of each is present? <span> I understand from Dr. Winiarski that the flow up
through the chimney is not symetrical and contains excess unmixed air.
</span>A 3D computer model of flowing gasses through the stove could allow ideas
to form for improved mixing of air with wood gas and flame. This could allow a
secondary burn using the excess preheated air already in the stove, and
perhaps some method of concentrating the flame for increased dwell time. A clean
burn is not necessarily hotter, but rather more complete. I agree with what you
said in an earlier e-mail, that a clean low soot flame requires excess air to
make sure all the fuel and soot is burned. The excess air cannot be allowed to
cool the flame, so using the excess preheated air that is already in the stove
is the way to go.<span> </span>With improved
mixing and dwell time, increasing flame temperature by radiating heat from the
wall could help.<u></u><u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt"><u></u> <u></u></span></p>
<p style="LINE-HEIGHT:normal;MARGIN:0in 0in 0pt" class="MsoNormal"><span style="FONT-FAMILY:'Arial','sans-serif';FONT-SIZE:14pt">Kirk</span><span style="FONT-FAMILY:'Times New Roman','serif';FONT-SIZE:14pt"><u></u><u></u></span></p>
<p style="MARGIN:0in 0in 10pt" class="MsoNormal"><span style="LINE-HEIGHT:115%;FONT-SIZE:14pt"><u></u><font face="Calibri"> </font><u></u></span></p></font></div>
<div><font size="2" face="Arial"></font> </div>
<blockquote style="BORDER-LEFT:#000000 2px solid;PADDING-LEFT:5px;PADDING-RIGHT:0px;MARGIN-LEFT:5px;MARGIN-RIGHT:0px" dir="ltr">
<div style="FONT:10pt arial">----- Original Message ----- </div>
<div style="FONT:10pt arial;BACKGROUND:#e4e4e4"><b>From:</b>
<a title="deankstill@gmail.com" href="mailto:deankstill@gmail.com" target="_blank">Dean
Still</a> </div>
<div style="FONT:10pt arial"><b>To:</b> <a title="stoves@lists.bioenergylists.org" href="mailto:stoves@lists.bioenergylists.org" target="_blank">Discussion of biomass cooking
stoves</a> </div>
<div style="FONT:10pt arial"><b>Sent:</b> Saturday, April 25, 2015 3:36
PM</div>
<div style="FONT:10pt arial"><b>Subject:</b> Re: [Stoves] Inner color of
combustion chamber?</div>
<div><br></div>
<div dir="ltr">Hi All,
<div><br></div>
<div>We were wondering if an inner refractory metal black wall would absorb
the IR (get very hot) and then emit back into</div>
<div>the fire. The outside of the metal wall would be shiny and then not emit
very much into the stove body?</div>
<div><br></div>
<div>Best,</div>
<div><br></div>
<div>Dean</div></div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Apr 24, 2015 at 3:12 PM, Bamboo Science Group
<span dir="ltr"><<a href="mailto:greg@bamboosciencegroup.com" target="_blank">greg@bamboosciencegroup.com</a>></span> wrote:<br>
<blockquote style="BORDER-LEFT:#ccc 1px solid;MARGIN:0px 0px 0px 0.8ex;PADDING-LEFT:1ex" class="gmail_quote">Dean<br>Great topic<br>When I was designing solar thermal
panels for INCO in 1979, we used a coating (selective) process (chrome oxide
spinel that had a alpha ( absorptivity) of 0.9 and and epsilon ( emissivity)
of 0.04) on stainless steel that allowed it to perform at parity with a
black oxide on copper ( fin and tube). The parity was achieved despite
the overwhelmingly superior conductance of copper versus s/s.<br>The high
alpha allows absorption of the short wave solar radiation and the low
epsilon slows the longer wave radiation emission in this flat plate solar
collector application. These "selective" surfaces have cavernous surface
area structure, utilizing the peaks and valleys of the coating to slow down
the emissivity of the longer wave radiation.<br><br>So you want an low
emissivity coating for your refractory material to reduce ( inhibit) the
black body radiation. SERI could certainly help out in this area as they are
acquainted with high-temperature selective coatings for their work on
concentrating collectors.<br><br>Sent from my iPad<br><br>> On Apr 24,
2015, at 5:07 PM, Dean Still <<a href="mailto:deankstill@gmail.com" target="_blank">deankstill@gmail.com</a>>
wrote:<br>><br>> Hi All,<br>><br>> At the Aprovecho weekly
meeting we were discussing how to improve performance in a Rocket stove. We
were wondering about radiation.<br>><br>> Would temperatures rise if
the inside of the refractory metal combustion chamber was black and the
outside shiny?<br>><br>> Best,<br>><br>> Dean<br>>
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