<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
Thanks for this Crispin. Your answers to Francois and Xavier have
helped me in my thought process with the project I envision here.
Love always, G<br>
<pre class="moz-signature" cols="72">Regards, Gerrie Baker, aka The Worm Lady
Dedicated to delivering organic waste solutions through education and demonstrations of worm composting habitats indoors and outside. Focused on converting garbage to gardens and encouraging people to grow their own healthy nutritious food and beautiful edible flowers.
The Worm Factory
874 Grady Road, Foley Mountain
Westport, ON K0G 1X0
613-273-7595
<a class="moz-txt-link-abbreviated" href="http://www.thewormfactory.ca">www.thewormfactory.ca</a></pre>
<br>
On 25/09/2011 11:40 AM, Crispin Pemberton-Pigott wrote:
<blockquote cite="mid:014e01cc7b99$788051f0$6980f5d0$@gmail.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<meta name="Generator" content="Microsoft Word 14 (filtered
medium)">
<style><!--
/* Font Definitions */
@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;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0mm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-US;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p.MsoPlainText, li.MsoPlainText, div.MsoPlainText
{mso-style-priority:99;
mso-style-link:"Plain Text Char";
margin:0mm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
p.MsoAcetate, li.MsoAcetate, div.MsoAcetate
{mso-style-priority:99;
mso-style-link:"Balloon Text Char";
margin:0mm;
margin-bottom:.0001pt;
font-size:8.0pt;
font-family:"Tahoma","sans-serif";
mso-fareast-language:EN-US;}
p.MsoNoSpacing, li.MsoNoSpacing, div.MsoNoSpacing
{mso-style-priority:1;
margin-top:5.0pt;
margin-right:0mm;
margin-bottom:5.0pt;
margin-left:0mm;
mso-add-space:auto;
font-size:11.0pt;
font-family:"Arial","sans-serif";
color:#1F497D;}
p.MsoNoSpacingCxSpFirst, li.MsoNoSpacingCxSpFirst, div.MsoNoSpacingCxSpFirst
{mso-style-priority:1;
mso-style-type:export-only;
margin-top:5.0pt;
margin-right:0mm;
margin-bottom:0mm;
margin-left:0mm;
margin-bottom:.0001pt;
mso-add-space:auto;
font-size:11.0pt;
font-family:"Arial","sans-serif";
color:#1F497D;}
p.MsoNoSpacingCxSpMiddle, li.MsoNoSpacingCxSpMiddle, div.MsoNoSpacingCxSpMiddle
{mso-style-priority:1;
mso-style-type:export-only;
margin:0mm;
margin-bottom:.0001pt;
mso-add-space:auto;
font-size:11.0pt;
font-family:"Arial","sans-serif";
color:#1F497D;}
p.MsoNoSpacingCxSpLast, li.MsoNoSpacingCxSpLast, div.MsoNoSpacingCxSpLast
{mso-style-priority:1;
mso-style-type:export-only;
margin-top:0mm;
margin-right:0mm;
margin-bottom:5.0pt;
margin-left:0mm;
mso-add-space:auto;
font-size:11.0pt;
font-family:"Arial","sans-serif";
color:#1F497D;}
span.PlainTextChar
{mso-style-name:"Plain Text Char";
mso-style-priority:99;
mso-style-link:"Plain Text";
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-CA;}
span.BalloonTextChar
{mso-style-name:"Balloon Text Char";
mso-style-priority:99;
mso-style-link:"Balloon Text";
font-family:"Tahoma","sans-serif";}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-US;}
.MsoPapDefault
{mso-style-type:export-only;
mso-margin-top-alt:auto;
mso-margin-bottom-alt:auto;}
@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]-->
<div class="WordSection1">
<p class="MsoPlainText">Dear François and Xavier<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">X Says >I strongly recommend you not
to use stainless steel for the combustion chamber, nor metal.
It won't last long. We saw it with our stoves, we used
conventional stainless steel. The chambers didn't last 2
months, they were deformed and ripped-off by the fire
intensity.<o:p></o:p></p>
<p class="MsoPlainText"><span style="color: black;"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="color: black;">Stainless
steel is 'stainless' mostly because it is not heated. It is
not technically 'heat resistant'. When the temperature rises
the chromium atoms cluster together ('condense') as soon as
they are mobile enough and form clumps. As their role was to
occupy 'oxidation sites' on the surface of the iron, so once
they are gone the oxidation sites are available once more,
and sure enough Oxygen attaches to them causing corrosion
(iron oxide) to form.<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;">Stainless
steel <i>can</i> be used in a high temperature fire as long
as it is continuously cooled by (usually) air passing behind
it. Putting insulation behind metal is a guarantee that the
chemistry will get completely messed up when hot, unless you
are using a high temperature steel (sometimes called a
temperature resistant steel) which is invariably very
(seriously) expensive. <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;">This type of
use of a cooling jacket was patented in the UK in 1947 when
an engineer made a hot water boiler with a 2mm wall in the
combustion chamber!<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;">So, if you
put the heat coming through the wall to work as a preheater
(especially for secondary air) you can in fact use steel as
a liner.<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;">If you are
building a Rocket-style stove with no separate secondary air
provision you are best off to use the hardest, densest,
lowest thermal expansion ceramic you can find for the
combustion chamber of an institutional stove. There is a
slight gain in combustion efficiency in the late fire when
using high mass bricks.<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;">If you find
that the heat loss is excessive (as a % of the total heat
produced) then consider insulating the hardened chamber, but
not until then and only then. Put the money into air control
instead.<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;">Usually the
idea of 'heat being lost' from the combustion chamber is
both overstated and uncalculated. Usually system efficiency
is not improved much at all by preventing some heat loss
from the combustion area. If that 'prevention' takes place
at a lifetime cost (reduced lifetime) then it is not worth
it as Xavier says, for stoves costing a couple of hundred
Dollars.<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;">Do not guess
what the heat loss prevention is. Calculate it. Painting it
silver on the outside might drop losses by 30%. If you find
that the difference in heat loss is 200 or 300 watts on a 15
kw stove, be very clear that it is FAR easier to transfer a
few hundred watts extra to the pot by controlling excess air
than it is to prevent its loss from a hot exterior of a
combustor.<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;">Most stoves
of the Rocket style have high excess air (due to no control
of air) so have a clear perspective on how much that EA
costs the system. If EA drops the system efficiency 10%,
then that little bit of heat lost to the surroundings low
down is 'peanuts'. Get a handle on the air supply. You can
choke it going in or choke it passing the pot (with tight
skirt). The effect is the same. The latter pressurises the
stove so it is more dangerous in a sealed room.<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;">So for any
system you intend to work for a long time, first seek
strength and thermal shock resistance, then look at the
thermal conductivity. Really hard bricks have a lousy
conductivity anyway and low density bricks are not all that
much better as insulators. The low density ones usually have
a very poor thermal shock resistance because they are not
dealing with the mechanical deformation. The ones used
industrially in high temperature applications are usually
cycled very slowly. A domestic or institutional stove
actually has a very difficult environment because the poor
suffering bricks are heated and cooled several times a day
across a huge temperature range.<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;">Regards<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color: black;">Crispin<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color: black;"><o:p> </o:p></span></p>
</div>
<pre wrap="">
<fieldset class="mimeAttachmentHeader"></fieldset>
_______________________________________________
Stoves mailing list
to Send a Message to the list, use the email address
<a class="moz-txt-link-abbreviated" href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</a>
to UNSUBSCRIBE or Change your List Settings use the web page
<a class="moz-txt-link-freetext" href="http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org">http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org</a>
for more Biomass Cooking Stoves, News and Information see our web site:
<a class="moz-txt-link-freetext" href="http://www.bioenergylists.org/">http://www.bioenergylists.org/</a>
</pre>
</blockquote>
</body>
</html>