<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML xmlns="http://www.w3.org/TR/REC-html40" xmlns:v =
"urn:schemas-microsoft-com:vml" xmlns:o =
"urn:schemas-microsoft-com:office:office" xmlns:w =
"urn:schemas-microsoft-com:office:word" xmlns:m =
"http://schemas.microsoft.com/office/2004/12/omml"><HEAD>
<META content="text/html; charset=utf-8" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 9.00.8112.16599"><!--[if !mso]>
<STYLE>v\:* {
BEHAVIOR: url(#default#VML)
}
o\:* {
BEHAVIOR: url(#default#VML)
}
w\:* {
BEHAVIOR: url(#default#VML)
}
.shape {
BEHAVIOR: url(#default#VML)
}
</STYLE>
<![endif]-->
<STYLE><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0mm;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman",serif;
color:black;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
p
{mso-style-priority:99;
mso-margin-top-alt:auto;
margin-right:0mm;
mso-margin-bottom-alt:auto;
margin-left:0mm;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0mm;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";
color:black;}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;
color:black;}
span.EmailStyle20
{mso-style-type:personal;
font-family:"Calibri",sans-serif;
color:#1F497D;}
span.EmailStyle21
{mso-style-type:personal;
font-family:"Calibri",sans-serif;
color:#1F497D;}
span.EmailStyle22
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></STYLE>
<!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></HEAD>
<BODY lang=EN-CA bgColor=white vLink=#954f72 link=#0563c1>
<DIV><FONT size=2 face=Arial>Crispin,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>My appology, I ment BLDD. Thank you for your
input.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Kirk</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@outlook.com
href="mailto:crispinpigott@outlook.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> Monday, December 15, 2014 9:36
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] Correcting a
misconception that approaches myth status</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
Kirk<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 class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; FONT-SIZE: 10pt">In a ND TLDD there
will always be a battle between the downward moving air and the hot combustion
gasses which will be inclined to rise. </SPAN><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; COLOR: #1f497d; FONT-SIZE: 10pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">I
need to be clear do you mean a Top lit down draft or a bottom lit downdraft? A
TLDD is not the same at all – that is like putting fuel on top of an existing
fire, except upside down. A BLDD is lit on the bottom and fuel added pushing
it down further. The MPF moves up.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">If
you meant BLDD, I will contribute this:<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; FONT-SIZE: 10pt">I am
thinking that gasses cannot go both directions in the same space, so will
there be areas in the fuel where the air will win and areas where the hot
gasses will win? </SPAN><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; COLOR: #1f497d; FONT-SIZE: 10pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">In
the small spaces, there is hot air buoyancy pushing gas and air up and there
is primary air passing down through the fuel. They fight. The passage down is
not completely even as it is in a TLUD where every force is upwards. In the
BLDD there are little currents of air and gas that rise, cool against the fuel
above then descend with the overall primary air flow down. The water vapour
and gases are pulled down eventually and have to pass through the permanent
char layer at the bottom, cracking the tars and so on to give a high H2 and CO
gas that burns below the grate. Ash falls down keeping the grate clear – a
significant advantage to low continuous operation. There are numerous
things that accentuate the quality of the gas burn. Adding preheated secondary
air is obviously one of them. There are a couple of recent patents on
optimising that burn at low EA.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; FONT-SIZE: 10pt">This could lead to
the buoyancy caused convection you mention, with the heavier air displacing
the hot gasses, pushing them upward. </SPAN><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; COLOR: #1f497d; FONT-SIZE: 10pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Correct.
This happens between the fuel particles. The vertical distance involved
depends on the primary air speed downwards. Generally, when the MPF reaches
the top of the fuel, the smoke and gases rise above the fuel and this means a
cover of some kind has to be placed over the hopper to prevent them getting
into the room. <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Here
is a picture of such a cover. The primary air hole is in the centre. It has to
be large enough not to block the primary air, but small enough to trap the gas
and smoke from the pyrolysis of the top layer of fuel inside the stove. The
upper hole is a secondary air flow controller (the plate is rotated to
regulate it).<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><IMG id=Picture_x0020_2
alt=cid:image004.jpg@01D018C7.07BA6900
src="cid:C12080F79F59475B97902165A8360C5A@phyllisPC" width=378
height=350><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Here
is an isometric view of a bottom lit downdraft stove (slightly different from
the one above) incorporating the same closer plate on
top.<o:p></o:p></SPAN></P>
<P class=MsoNormal><IMG id=Picture_x0020_1
alt=cid:image005.jpg@01D018C7.07BA6900
src="cid:0C736E2757A744DEA52242B6A5AA4518@phyllisPC" width=472
height=361><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; FONT-SIZE: 10pt">Could this
unevenness be caused by local resistance variations to gas flow
in the fuel? </SPAN><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; COLOR: #1f497d; FONT-SIZE: 10pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">I
don’t think that is an aspect of the circulation. It is just hot gases rising,
cooling against the fuel above and descending again. It also takes place in
cross draft stoves with a hopper. In that case the pyrolysation front is
approximately stationary and there is no air from above passing down through
the fuel in the hopper. The reason is that a cross draft stove would not bring
enough air through the fuel to keep the pyrolysation front from rising through
the entire hopper. The hopper top is sealed and the layer is starved of air,
able only to get air from below rising through the fuel then descending again
– perhaps 80mm or so.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial',sans-serif; FONT-SIZE: 10pt">Or might it be a
temperature thing where the air wins in cooler areas and the hot gasses
win in hotter areas? Or am I totally off base
here?</SPAN><o:p></o:p></P></DIV>
<DIV>
<P class=MsoNormal><SPAN style="COLOR: #1f497d"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">That
is completely on-base. <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Here
is a photo of a stove taken at night when the MPF has moved halfway up through
the fuel.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><IMG id=Picture_x0020_3
alt=cid:image009.jpg@01D018C7.07BA6900
src="cid:4DAE38A18FDE40CBAD82A9837431E849@phyllisPC" width=378
height=417><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">The
hopper is 2mm thick 3CR12 which can operate at that temperature for sustained
periods. All this work was performed at the SeTAR Centre research lab at the
University of Johannesburg.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">The
MPF can be made much thinner than above by using chipped fuel. The main reason
for chips making it thinner is that the upward movement of hot gases is
limited by the compacting of the fuel. They cool more quickly in the small
passages.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">All
these stoves have a minimum power level (same as a viable TLUD fire) and it is
related to the particle size. Bigger means higher minimum power. If the
particle size is larger than 1/6<SUP>th</SUP> of the hopper diameter the fire
is likely to pyrolyse the fuel then go out. That is experience and observation
talking, there is no theory behind it. It just gets too
cold.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Regards<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Crispin<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P></DIV></DIV>
<P>
<HR>
<P></P>_______________________________________________<BR>Stoves mailing
list<BR><BR>to Send a Message to the list, use the email
address<BR>stoves@lists.bioenergylists.org<BR><BR>to UNSUBSCRIBE or Change
your List Settings use the web
page<BR>http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org<BR><BR>for
more Biomass Cooking Stoves, News and Information see our web
site:<BR>http://stoves.bioenergylists.org/<BR><BR></BLOCKQUOTE></BODY></HTML>