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<DIV><FONT color=#1f497d><FONT face=Calibri>>Crispin said: An implementation
that most will find useful is to extend the burner higher than the top deck as
you have done, then have the larger gap, then put a ring of similar height (a
little higher) at about the OD of the pot. </FONT></FONT></DIV>
<DIV><FONT color=#1f497d><FONT face=Calibri></FONT></FONT> </DIV>
<DIV><STRONG><FONT size=4 face=Arial>Crispin you are a mind reader or maybe
you have already done this, because <U>that</U> is exactly what I plan to
do with the next potholder prototype. The burner extends above the cooktop about
25 mm and the potholder will be about 12 to 18 mm or about 1/2 to 5/8
taller. (I am decreasing the gap from 25 mm to about 12 to18 mm to help the flow
spread out around the pot) <U>and then around the outside parameter of the
potholder I will use a band about 25 mm, to trap the dead
air.</U></FONT></STRONG></DIV>
<DIV>
<DIV><STRONG><FONT size=4 face=Arial>My cook top extends beyond the pot holder
and pot so the "Pot Shell" will have a place to sit. The pot shell is the
easiest way to improve a stoves efficiency. Without the pot shell, my
stove would not be able to boil, and then simmer, 35 Kg of beans for 2
hours with only 3 Kg of wood.</FONT></STRONG></DIV></DIV>
<DIV><STRONG><FONT size=4 face=Arial>I am also working on a multiple pot,
potholder that sits on a single burner and is able to direct the heat flow in 2
or 3 different directions. This pot holder will have a 250 mm/10" flat spot
above the burner that could be used like a small griddle. Hinged flaps/doors
will direct the flow. </FONT></STRONG></DIV>
<DIV><STRONG><FONT size=4 face=Arial>Lanny</FONT></STRONG></DIV>
<DIV><FONT color=#1f497d><FONT
face=Calibri><o:p></o:p></FONT></FONT> </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=crispinpigott@gmail.com href="mailto:crispinpigott@gmail.com">Crispin
Pemberton-Pigott</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=stoves@lists.bioenergylists.org
href="mailto:stoves@lists.bioenergylists.org">'Discussion of biomass cooking
stoves'</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Sunday, September 22, 2013 2:39
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] A doctoral thesis
on stoves</DIV>
<DIV><BR></DIV>
<DIV class=WordSection1>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Dear
Lanny<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<DIV>
<P style="MARGIN: 0mm 0mm 0pt" class=MsoNoSpacing><B><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 13.5pt">With the School
Lunch Cooker I let the burner extend 1”/25mm above the cook top and used
2”/50mm tall pot holders. This puts the heat on the pot and shields the stove
top with a layer of dead air.<o:p></o:p></SPAN></B></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">I
have another interpretation that may be useful. You did the right thing, but
the layer of air is not at all dead. What happens is that the buoyancy of the
hot molecules is much stronger than the effect of turbulence. Even though the
gap under the pot is large, it is not hot ‘down there’ on the lower surface.
The heat rapidly rises into the pot. An implementation that most will find
useful is to extend the burner higher than the top deck as you have done, then
have the larger gap, then put a ring of similar height (a little higher) at
about the OD of the pot. <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">This
creates a heat transfer zone that is not easily blown around by transient
winds.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">The
suggestion that the space should be small with a high velocity to bring the
heat close to the pot is based on the presumption that the hottest molecules
do not rise with more force than the turbulent force. In fact the buoyancy
force is about 30 times the turbulent force. The heat is always at the top
when the flow is in the 200 mm/sec range. “Top” in this case means the top 2mm
of the cross section. It is cool right at the surface where the heat flux is
taking place.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">The
suggestion that ‘more heat’ gets into the pot if the velocity is high confuses
the heat transfer rate with the heat transfer efficiency. They are both
efficiencies (ratios) but of different things.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Regards<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Crispin<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P></DIV></DIV>
<P>
<HR>
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