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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Dear Crispin,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I’m surprised the paint color on the
outside would make much difference. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Lets see if I have this right. As the goal
is to keep the heat inside the stove body we want less radiation to the outside
off the paint. So more heat on the outside surface the more loss from the
inside stove unless the loss is greater than the heat being supplied from the
stove (not likely(?)). So its not the thickness of the paint and insulating
material of the paint but the color of the surface that makes a big
difference(?) as to how fast the heat will radiate to the outside air(?). <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>And thanks for the info on purchase of an
IR thermometer having an emissivity setting as I am about to purchase one. Any
suggestions?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Again - lots of great information. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thanks<o:p></o:p></span></font></p>
<p class=MsoNormal><st1:PersonName w:st="on"><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>Frank</span></font></st1:PersonName><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Comment below:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><st1:PersonName w:st="on"><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>Frank</span></font></st1:PersonName><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'> Shields</span></font><font color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Control Laboratories, Inc.</span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><st1:Street w:st="on"><st1:address w:st="on"><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>42 Hangar Way</span></font></st1:address></st1:Street><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><st1:place w:st="on"><st1:City w:st="on"><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>Watsonville</span></font></st1:City><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>, <st1:State
w:st="on">CA</st1:State> <st1:PostalCode w:st="on">95076</st1:PostalCode></span></font></st1:place><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>(831) 724-5422 tel</span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>(831) 724-3188 fax</span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="mailto:frank@compostlab.com">frank@compostlab.com</a></span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="http://www.compostlab.com">www.compostlab.com</a></span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Calibri><span style='font-size:
11.0pt;color:navy'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Calibri><span style='font-size:
11.0pt;color:navy'> </span></font><o:p></o:p></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
stoves-bounces@lists.bioenergylists.org
[mailto:stoves-bounces@lists.bioenergylists.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Crispin Pemberton-Pigott<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, September 15, 2011
1:14 PM<br>
<b><span style='font-weight:bold'>To:</span></b> '<st1:PersonName w:st="on">Discussion
of biomass cooking stoves</st1:PersonName>'<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Stoves] flames
touching pot</span></font><font size=3 face="Times New Roman"><span
style='font-size:12.0pt;font-family:"Times New Roman"'><o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=2 face=Calibri><span style='font-size:11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>Dear <st1:PersonName w:st="on">Frank</st1:PersonName><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>Good to hear from you.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>During the early days of solar agitation
(in the ‘70’s) it was discovered that one of the most effective colours for
picking up (or radiating) solar insolation was a dull yellow. Big surprise.
Some browns are also very efficient. They were not selective coatings such as
are used in the evacuated glass pipes on Chinese coated solar water heaters.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>Your bright red is probably a pretty
good radiator, in spite of being slightly ‘white-ish’.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>The main thing is to borrow an IR
thermometer (which you in particular you should already have) and check the
difference between the contact thermocouple reading and the IR reading with the
emissivity set to 0.93 (most common default) or 0.95 (secondmost common).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>You don’t really need to know the value,
you want to know if there is a change, and in which direction.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>I strongly suspect that your darkened
paint will radiate more heat than the bright paint and the difference between
the two readings will be reduced.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>Remember that the heat convection from
the same surface will be reduced if the radiation increases, and the surface
temperature will drop. Don’t assume that if the dark area is cooler it is losing
less heat.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>This is either counter-intuitive or
confuse-intuitive for most people. A higher surface temperature (with the same
system insulation value) usually means a lousier heat loss. Low temperatures on
the outside of a stove do <i><span style='font-style:italic'>not</span></i>
mean it is not losing heat, it may just be losing it very efficiently!<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>Always calculate…<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>If you buy an IR thermometer, make sure
it has an adjustable emissivity setting, typically from 0.4 to 1.0 or 0.35 to
1.0. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>New galv metal has a very low </span></font><font
color="#1f497d" face="Lucida Sans Unicode"><span lang=EN-CA style='font-family:
"Lucida Sans Unicode";color:#1F497D'>ɛ</span></font><font color="#1f497d"><span
lang=EN-CA style='color:#1F497D'> value. Many small sheet metal stoves work
much better when new than later because of this. They can’t get rid of heat
easily when shiny. This leads to higher secondary air preheating and lower
losses from radiation. Later th</span></font><font color="#1f497d"><span
lang=EN-CA style='color:#1F497D'>e losses increase in both parameters.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>For those who want to get rid of heat
from hot surface (over 200 C) use a crosslinking silicone paint. It needs to be
stirred a lot before use. Available in white and dark grey, it will survive 540
°C indefinitely. It is painted on and dries extremely quickly. Fresh black
looks black. When heated over 200 is crosslinks, turns grey and is thereafter
really hard to get off. It is not waterproof if painted on with a brush in only
one coat. One brand name is HRA 540 from Dulux. We use it on the Basintuthu
Stove and the guys making institutional baking ovens in <st1:country-region
w:st="on"><st1:place w:st="on">Lesotho</st1:place></st1:country-region>
designed by Peter Scott switched to it once they were told it existed. <st1:City
w:st="on"><st1:place w:st="on">Normal</st1:place></st1:City> (enamel) black
paint burned off quickly exposing things to rust. In most cases you can
use it on pot grates above the fire. It has the same heat resistant
capabilities as silicone coated 600 degree electrical wire which is quite
common so you know what to expect.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>Regards<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'>Crispin<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
stoves-bounces@lists.bioenergylists.org [mailto:stoves-bounces@lists.bioenergylists.org]
<b><span style='font-weight:bold'>On Behalf Of </span></b><st1:PersonName
w:st="on">Frank</st1:PersonName> Shields<br>
<b><span style='font-weight:bold'>Sent:</span></b> 15 September 2011 13:34<br>
<b><span style='font-weight:bold'>To:</span></b> '<st1:PersonName w:st="on">Discussion
of biomass cooking stoves</st1:PersonName>'<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Stoves] flames
touching pot<o:p></o:p></span></font></p>
</div>
</div>
<p class=MsoNormal><font size=2 face=Calibri><span lang=EN-CA style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Dear Crispin, <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>My GEK was painted bright fire engine red
with some special paint. The paint changed color from red to gray-black around
the lower area. What does that tell us? And can painted surfaces effect or be
good indicators of how hot a surface is(?) or the e value? <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Great info –thanks<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><st1:PersonName w:st="on"><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>Frank</span></font></st1:PersonName><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><st1:PersonName w:st="on"><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>Frank</span></font></st1:PersonName><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'> Shields</span></font><font color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Control Laboratories, Inc.</span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><st1:Street w:st="on"><st1:address w:st="on"><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>42 Hangar Way</span></font></st1:address></st1:Street><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><st1:place w:st="on"><st1:City w:st="on"><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>Watsonville</span></font></st1:City><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>, <st1:State
w:st="on">CA</st1:State> <st1:PostalCode w:st="on">95076</st1:PostalCode></span></font></st1:place><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>(831) 724-5422 tel</span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>(831) 724-3188 fax</span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="mailto:frank@compostlab.com">frank@compostlab.com</a></span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="http://www.compostlab.com">www.compostlab.com</a></span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Calibri><span style='font-size:
11.0pt;color:navy'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Calibri><span style='font-size:
11.0pt;color:navy'> </span></font><o:p></o:p></p>
</div>
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face="Times New Roman"><span style='font-size:12.0pt;font-family:"Times New Roman"'>
<hr size=2 width="100%" align=center>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> stoves-bounces@lists.bioenergylists.org
[mailto:stoves-bounces@lists.bioenergylists.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Crispin Pemberton-Pigott<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, September 14,
2011 7:50 PM<br>
<b><span style='font-weight:bold'>To:</span></b> '<st1:PersonName w:st="on">Discussion
of biomass cooking stoves</st1:PersonName>'<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Stoves] flames
touching pot</span></font><font size=3 face="Times New Roman"><span
style='font-size:12.0pt;font-family:"Times New Roman"'><o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=2 face=Calibri><span style='font-size:11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face=Calibri><span lang=EN-CA
style='font-size:11.0pt'>Dear Paul and AJH<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face=Calibri><span lang=EN-CA
style='font-size:11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face=Calibri><span lang=EN-CA
style='font-size:11.0pt'>AJH >I don't for sure but dull red is around
600-700C for a black body, I'd guess stainless would be around 0.9 emissivity ,
so a bit hotter, of course the outside is losing heat by radiation, conduction
and convection so the other side of the steel can be hotter.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>That would be a bit high for stainless
unless it is badly darkened. Before jumping in with a number I wondered if you
had checked a few values with a surface contact thermocouple. The low chrome
stainless steels darken quite a bit at high temp so the surface finish
dominates (it can still be shiny). Discoloured 400 series is still pretty low.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Engineering toolbox says:<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Values of </span></font><font size=4
color=black face="Lucida Sans Unicode"><span lang=EN-CA style='font-size:14.0pt;
font-family:"Lucida Sans Unicode";color:black'>ɛ</span></font><font
color=black><span lang=EN-CA style='color:black'><o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Steel Oxidized
0.79<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Steel Polished
0.07<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Stainless Steel,
weathered 0.85<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Stainless Steel,
polished
0.075<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Stainless Steel, type
301
0.54 - 0.63<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Steel Galvanized
Old
0.88<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Steel Galvanized
New
0.23<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>I have attached a photo of a fuel hopper
made of 3CR12 which has a rough surface but is reasonably white. The </span></font><font
size=4 color=black face="Lucida Sans Unicode"><span lang=EN-CA
style='font-size:14.0pt;font-family:"Lucida Sans Unicode";color:black'>ɛ</span></font><font
color=black><span lang=EN-CA style='color:black'> is about 0.75 maybe less.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>I am speaking up on the subject because it
can be quite dangerous for children if there are stainless steel components of
a stove that can be touched. They have such difficulty getting rid of heat that
the temperature is very high before it does so. On the other hand the inability
to radiate away significant heat and the poor conduction coefficient (about ½
that of mild steel) means stainless is a pretty good insulating and therefore
combustion chamber material if it is not further insulated on the back.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>In the attached photo of a BLDD5.2 from
the SeTAR Centre the temperature inside is far above the outside surface in
spite of the significant heat radiating away from the outside (making it
visible to the camera). So it has the advantages of being strong, corrosion
resistant, hot and insulating with a poor radiation coefficient. This
combination works best when the whole system is small and when the oxygen level
in the hot region is low.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>We make bread ovens from stainless steel
with a bright finish and the </span></font><font size=4 color=black
face="Lucida Sans Unicode"><span lang=EN-CA style='font-size:14.0pt;font-family:
"Lucida Sans Unicode";color:black'>ɛ</span></font><font color=black><span
lang=EN-CA style='color:black'> is 0.4 when it is new.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>For those who are not familiar with the
term “</span></font><font size=4 color=black face="Lucida Sans Unicode"><span
lang=EN-CA style='font-size:14.0pt;font-family:"Lucida Sans Unicode";
color:black'>ɛ</span></font><font color=black><span lang=EN-CA
style='color:black'>” it is used in the formula that calculates how much heat
radiates away from a surface into the surrounding environment. It is called
‘grey body radiation’ because things are not truly black. The formula is </span></font><font
size=4 color=black face="Lucida Sans Unicode"><span lang=EN-CA
style='font-size:14.0pt;font-family:"Lucida Sans Unicode";color:black'>ɛ</span></font><font
color=black><span lang=EN-CA style='color:black'> * 5.6703*10<sup>-8</sup>*
Temperature in Deg Kelvin * surface area in sq metres.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>If you want to try something interesting,
make up a case with an </span></font><font size=4 color=black
face="Lucida Sans Unicode"><span lang=EN-CA style='font-size:14.0pt;font-family:
"Lucida Sans Unicode";color:black'>ɛ</span></font><font size=4 color=black><span
lang=EN-CA style='font-size:14.0pt;color:black'>,</span></font><font
color=black><span lang=EN-CA style='color:black'> a temperature and an area.
Then lower the </span></font><font size=4 color=black face="Lucida Sans Unicode"><span
lang=EN-CA style='font-size:14.0pt;font-family:"Lucida Sans Unicode";
color:black'>ɛ</span></font><font color=black><span lang=EN-CA
style='color:black'>. You will see the heat radiating drop proportionally. Then
increase the temperature until the radiated heat equals the original case. You
will be surprised. A low emissivity surface has to be a lot hotter to radiate
the same energy as a high emissivity one. That is why cast iron stoves are
painted and polished flat black. In real life the convective heat transfer
increases with the temperature as well so it is not so straight forward to get
accurate numbers.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Regards<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'>Crispin<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 color=black face=Calibri><span lang=EN-CA
style='font-size:11.0pt;color:black'><o:p> </o:p></span></font></p>
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