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Marc,<br>
Would you care to take the next step and calculate what happens to
gas temperature and convective heat transfer with the dome?<br>
Just a thought........experiment.<br>
<br>
Thanks for shedding light with your radiant contribution.<br>
Alex<br>
<br>
On 17/03/2012 8:30 AM, Marc Pare wrote:
<blockquote
cite="mid:CAPJQZbyFQ+GbbwkY_+vLDh9KcVbAo8t54Xg1u8uuB5HY-Dwc8A@mail.gmail.com"
type="cite">
<div>Hi all,</div>
<div><br>
</div>
<div>First a short story, then a presentation of some analysis
I've been working on the last week (with the help of Crispin and
Matt Redmond). You can skip the story, if you like.</div>
<div><br>
</div>
<div><b>the story</b></div>
<div>My friend Isaac from Tech tells of his
most traumatic experience training to be an engineer: "We were
giving a presentation on a design of a hybrid vehicle. The
professor asks us why we choose one particular motor over
another. 'Oh, it was bigger, so we figured it would be better.'
The professor stopped them there. Stood up, turned to the class,
and yelled: "ENGINEERS QUANTIFY!"</div>
<div><br>
</div>
<div><b>the results</b></div>
<div>In the spirit of Isaac's legendary professor, I sought to
provide some clarity to the speculation of radiative heat
transfer and improved cook stoves by doing some simple analysis.</div>
<div><br>
</div>
<div>The setup was simple: what is the theoretical upper bound on
contribution to heat transfer by the "dome-shaped emitter"
described over the last week.</div>
<div><br>
</div>
<div>It turns out that <b>the dome-shaped emitter has negligible
impact on the heat transfer</b>. Further testing supported
this conclusion, but I figured it was worth showing how we were
able to show with theory that the dome-shaped thing was not
important.</div>
<div><br>
</div>
<div>The results place the upper bound on power from the emitter
at <b>0.301 kW </b>vs. the power required to boil water at <b>1.65
kW</b>.</div>
<div>This means that even at 100% efficiency, the emitter will
only improve your thermal performance by about 20%. (not the
reported 100% improvement)</div>
<div><br>
</div>
<div>I attached a pdf explaining the theory and a spreadsheet of
the calculation. You can also get them here:</div>
<div><a moz-do-not-send="true"
href="http://notwandering.com/radiation.php">http://notwandering.com/radiation.php</a> <br>
</div>
<div><br>
</div>
<div><b>thanks</b></div>
<div>Matt Redmond for a first pass on the spreadsheet</div>
<div>Crispin for quadruple-checking the spreadsheet and adding
improved water boiling numbers</div>
<div><br>
</div>
<div>
<br>
</div>
<div>feedback is welcome. there is always the chance that there
are mistakes!</div>
<div><br>
</div>
<div>Best,</div>
<br clear="all">
Marc Paré<br>
B.S. Mechanical Engineering<br>
Georgia Institute of Technology | Université de Technologie de
Compiègne<br>
<br>
my cv, etc. | <a moz-do-not-send="true"
href="http://notwandering.com" target="_blank">http://notwandering.com</a><br>
<br>
<br>
<div class="gmail_quote">On Sat, Mar 17, 2012 at 2:05 PM, Crispin
Pemberton-Pigott <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:crispinpigott@gmail.com">crispinpigott@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div link="blue" vlink="purple" lang="EN-CA">
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Great!</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Marc
you are doing us a great service. Simply by collecting
the little spreadsheets circulated here, one can gain a
good education in stove design.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The
volunteer’s efforts are always rewarded.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Many
thanks</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Crispin</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<div>
<p class="MsoNormal"><span style="color:#1f497d">+++++++</span></p>
<div>
<div class="h5">
<p class="MsoNormal"># I appeal to Marc not to hide
his light under a bushel. These discussion also need
numbers and methods so the reality of things becomes
widespread.</p>
</div>
</div>
</div>
<div>
<div class="h5">
<p class="MsoNormal"><br clear="all">
Write-up is coming :)</p>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">Putting
in some effort so that it's a useful resource for
folks in the future.</p>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">Marc
Paré<br>
B.S. Mechanical Engineering<br>
Georgia Institute of Technology | Université de
Technologie de Compiègne<br>
<br>
my cv, etc. | <a moz-do-not-send="true"
href="http://notwandering.com" target="_blank">http://notwandering.com</a><br>
<br>
</p>
<div>
<p class="MsoNormal">On Sat, Mar 17, 2012 at 1:55
PM, Crispin Pemberton-Pigott <<a
moz-do-not-send="true"
href="mailto:crispinpigott@gmail.com"
target="_blank">crispinpigott@gmail.com</a>>
wrote:</p>
<div>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Dear
Alexis and Paul</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Thanks
so much for the very open discussion and
open design of the burners. Alexis, when we
met in Thailand you mentioned that you have
switched to a premixed flame and if you
recall we did talk a bit about the top end
of the version of the stove you
demonstrated.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Is
it correct that you are now using a premixed
flame? I have been in extensive conversation
with Paul O about the burner for some time
and it seems at present to be a blend of
premixing with secondary air and as Paul
says, some tertiary air for the final
burnout.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The
difference in performance that Paul
mentioned and which got some much discussion
going about heat transfer from the hot dome
could have at least three quite different
origins and there is a lot of merit in
tracking down the difference. The first
might be that the structure under the pot on
Paul’s present configuration is much more
closed than the one I saw in Thailand. That
could account for all the difference in the
boiling time. A second possibility is the
reduction in excess air either through the
burner where flames are present or between
the flames and the final departure of the
pot and stove structure, by which I mean the
outer ring. Until the hot gases leave the
pot and vent into the room, the air present
in that gas stream is technically part of
the combustor. If there is a lot of cold air
entering the region under the pot, then it
is counted as excess air in the heat
exchanger.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Paul,
thanks for putting the pictures of the
development work you are doing. It is
helpful for those who would like to work on
stoves with minimal equipment to see how
things work and what has been tried. It
saves a lot of reinventing.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">With
regard to the heat transfer from a radiant
dome, Marc has been doing some calculations
which I hope he will post here when he is
confident in the method. That should settle
the question as to whether or not a large
increase in performance can be obtained by
changing hot, relatively non-IR radiant gas
into IR emitted from a wide gauze surface.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">It
is well worth remembering that because a
flame is pale blue in the visible range,
that does not tell us what it is emitting in
the IR which is invisible to human eyes.
Looking through a translucent flame is not
really a measure of emissions of heat. If
you point an IR gun at a flame it will
register a high temperature, even if it is
as inaccurate as an unshielded thermocouple.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I
agree with the others that the discussion
about heat transfer has been a good
exploration of the subject. I appeal to Marc
not to hide his light under a bushel. These
discussion also need numbers and methods so
the reality of things becomes widespread.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Regards</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Crispin</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</blockquote>
</div>
<br>
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