<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.19190">
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial>Dear Matthew</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>It is amazing how something so simple can escalate to
something wonderfully intriguing!! :-)</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Firstly, the "ordinary mirror" is a bit complex. The
silvered surface is on the "far side" of the glass. Window
glass is opaque to both UV and IR radiation. The "mirrored surface" on the
far side of the mirror glass likely does not enter into the situation at
all.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Note that, as Crispin pointed out, the red laser with a
"laser thermometer" is simply a visible pointing aid. It merely points to
the center of the surface being "surveyed" by the IR temperature sensor in the
instrument. </FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Please see: <A
href="http://www.holanengineering.com/sitebuildercontent/sitebuilderfiles/emissivity_1.pdf">http://www.holanengineering.com/sitebuildercontent/sitebuilderfiles/emissivity_1.pdf</A> for
a very complete listing of the emissivities of many materials at various
temperatures and surface conditions. We see that the surface emissivity of
smooth glass is .95 between 0 and 200 C. Thus, the surface temperature of
the glass is 95% of a "perfect emitting surface". Note also under a
following section "Paint, Lacquer, Varnishes" that the emissivities of surfaces
painted with oil based paints varies from .92 to .96, with 16 different colors
being tested. </FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Note that my "laser thermometer is a cheap one... $29 from
Canadian Tire (also known as "Cambodian Tire" :-) It is not one I would rely on
to make conclusive statements with relatively small temperature differences.
However, I must say that in certain circumstances, it is very accurate. I
measured the temperature of a batch of wine I was aging in a 5 gallon
carboy, and with a mercury thermometer, reading 64 degrees, the Laser
Temperature was also 64 degrees when pointed at the wine surface, AND also, 64
degrees, when pointed at the glass walls of the carboy. </FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I tried the Aluminium Foil Experiment, as you suggested. I
hung the foil in direct contact with the mirror surface, with "shiny side out."
Temperature readings were as follows:</FONT></DIV>
<DIV><FONT face=Arial>1: Temperature of a "far wall" 58.0 F</FONT></DIV>
<DIV><FONT face=Arial>2: Temperature 58.7 F, when front of instrument was held
in direct contact with the mirror (emissivity ~ .95</FONT></DIV>
<DIV><FONT face=Arial>3: Temperature 71.3 F, when front of instrument was held
in direct contact with the Aluminium foil, which was in direct contact with the
mirror. (emissivity ~ .1)</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I then repeated the experiment, using a CD. I placed the
disk on a table for it to equilibrate in temperature, and then with the face
of the instrument in direct contact with the CD, I got the following
readings:</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Temperature 62.6 F, when reading the "Painted Side"
(emissivity ~ .9)</FONT></DIV>
<DIV><FONT face=Arial>Temperature 59.7 F, when reading the "Shiny
Side" (emissivity ~ .1)</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>That is interesting, in that with "foil test" and the
"CD test", the differences in emissivities were similar, but for the CD
Test, temperature readings were not at all like those observed with the "foil
test." </FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>At any rate, these simple tests seem to raise more
questions than providing answers. :-(</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Best wishes,</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Kevin</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV>----- Original Message ----- </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"
dir=ltr>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=mredmond3@gatech.edu href="mailto:mredmond3@gatech.edu">Matthew
Redmond</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=stoves@lists.bioenergylists.org
href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, March 08, 2012 3:18
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] radiant heat
capture, total heat measurement</DIV>
<DIV><BR></DIV>
<DIV class=gmail_quote>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>Kevin,<BR></BLOCKQUOTE>
<DIV><BR></DIV>
<DIV>Nice experiment with the cheap laser thermometer. You are correct,
the laser thermometer did have a higher reading when measuring off your hand,
but it was not as high as would be expected with a very reflective surface
like a mirror. </DIV>
<DIV><BR></DIV>
<DIV>The reason for this could be that your thermometer measures temperature
based on IR wavelengths, not visible wavelengths. Though the mirror
surface reflected visible light very well (we can see this), how do you know
for sure it reflected IR light? In fact, if the mirror was covered with glass,
then the mirror actually is NOT reflective to IR light. That is because
glass is an absorptive medium for IR light. </DIV>
<DIV><BR></DIV>
<DIV>Try repeating your experiment using a shiny metal surface (like aluminum
foil). Aluminum foil is reflective of both visible and IR wavelengths.
You may find different results.</DIV>
<DIV><BR></DIV>
<DIV>If anyone is interested in learning more about radiation heat transfer, I
highly recommend reading the articles on "Black body radiation", "Emissivity",
"Reflectivity" and "View Factor" available on Wikipedia. </DIV>
<DIV><BR></DIV>
<DIV>-Matt Redmond</DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>><BR>><BR>> -----Original Message-----<BR>>
From: <A
href="mailto:stoves-bounces@lists.bioenergylists.org">stoves-bounces@lists.bioenergylists.org</A><BR>>
[mailto:<A
href="mailto:stoves-bounces@lists.bioenergylists.org">stoves-bounces@lists.bioenergylists.org</A>]
On Behalf Of Kevin<BR>> Sent: Wednesday, March 07, 2012 8:32 PM<BR>>
To: Discussion of biomass cooking stoves<BR>> Subject: Re: [Stoves]
radiant heat capture, total heat measurement<BR>><BR>> Dear
Frank<BR>><BR>> OK... basically, a surface radiates or absorbs energy
as a function of its<BR>> emissivity. A "Black Body" is such a perfect
radiation and absorption<BR>> surface. It has an Emissivity of 1.00 Good
"real world absorbers" have an<BR>> emissivity in the range of about .9
to .95, while "poor real world<BR>> absorbers" have an emissivity in the
range of about .02 to .05. These Poor<BR>> absorbers" are thus "excellent
reflectors."<BR>><BR>> With this as an "opener", see further comments
within your text below....<BR>><BR>> ----- Original Message
-----<BR>> From: "Frank Shields"<<A
href="mailto:frank@compostlab.com">frank@compostlab.com</A>><BR>> To:
"'Discussion of biomass cooking stoves'"<BR>> <<A
href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</A>><BR>>
Sent: Wednesday, March 07, 2012 8:30 PM<BR>> Subject: Re: [Stoves]
radiant heat capture, total heat measurement<BR>><BR>><BR>>>
Dear Kevin<BR>>><BR>>> That is what I was wondering. But that is
then a 'new' heat source(?).<BR>>> Correct?<BR>> # No, it is not a
"new" heat source. The mirror, perhaps having an<BR>> emissivity of .05
would simply reflect .95 of teh radiant energy landing on<BR>>
it.<BR>><BR>> That shinny surface must be hotter than the next
surface being.<BR>><BR>> # It would be marginally hotter than its
immediate surroundings, in that it<BR>> reflected only 95% of teh radiant
energy that fell on it. the heat is NOT<BR>> so much a source of
"radiant heat", but rather "reflected radiant heat."<BR>><BR>>>
heated up by the radiant heat it then gives off. OR can you reflect
heat<BR>>> to<BR>>> another surface without heating the surface
doing the reflecting?<BR>> # Yes, if you had a surface with 0.0
Emissivity... you would have a 100%<BR>> efficient reflector, with no
energy absorption.<BR>><BR>> Then when<BR>>> measuring
that shinny surface using an IR gun it reads low heat but the<BR>>>
surface it reflecting too will read higher heat? Is that
possible?<BR>>><BR>> # I did an interesting experiment as
follows:<BR>> I have a flat mirror on a wall. I have a cheap "Laser
Thermometer", which<BR>> when pointed to the wall beside the mirror
reads<BR>> : 45 degree angle: 55 F<BR>> 90 degree angle 55
F<BR>><BR>> # When pointed at teh mirror,<BR>> 45 degree angle 55
F<BR>> 90 degree angle 56 F<BR>><BR>> #When pointed at my hand, I
read 92 degrees F<BR>> When pointed to the mirror, but with the reflected
red dot hitting my hand,<BR>> I read 60 F<BR>> When I remove my hand
from the path of teh reflected beam and the red dot<BR>> hits teh wall, I
read 57<BR>><BR>> # I conclude that:<BR>> 1: This cheap "Laser
Thermometer is actually very good.<BR>> 2: It appears to correct for the
different emissivities of a mirrored<BR>> surface, e=.05, and a wall,
e=.9<BR>> 3: It measures the surface temperature of the mirror, and not
the<BR>> temperature of teh reflected surface.<BR>> 4: However, while
it "mostly measures the mirror surface, the "reflected<BR>> measurement"
of my hand temperature was a bit above room temperature.<BR>><BR>> #
Perhaps others will have a different interpertation of my little
test?<BR>><BR>> Best wishes,<BR>><BR>>
Kevin<BR>><BR><BR></BLOCKQUOTE></DIV><BR>
<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://www.bioenergylists.org/<BR><BR>
<P>
<HR>
<P></P><A></A>
<P align=left color="#000000" avgcert??>No virus found in this
message.<BR>Checked by AVG - <A
href="http://www.avg.com">www.avg.com</A><BR>Version: 2012.0.1913 / Virus
Database: 2114/4858 - Release Date: 03/08/12</P></BLOCKQUOTE></BODY></HTML>