Dear Frank
OK... basically, a surface radiates or absorbs energy as a function of its
emissivity. A "Black Body" is such a perfect radiation and absorption
surface. It has an Emissivity of 1.00 Good "real world absorbers" have an
emissivity in the range of about .9 to .95, while "poor real world
absorbers" have an emissivity in the range of about .02 to .05. These Poor
absorbers" are thus "excellent reflectors."
With this as an "opener", see further comments within your text below....
----- Original Message -----
From: "Frank Shields" <[email protected]>
To: "'Discussion of biomass cooking stoves'"
<[email protected]>
Sent: Wednesday, March 07, 2012 8:30 PM
Subject: Re: [Stoves] radiant heat capture, total heat measurement
Dear Kevin
That is what I was wondering. But that is then a 'new' heat source(?).
Correct?
# No, it is not a "new" heat source. The mirror, perhaps having an
emissivity of .05 would simply reflect .95 of teh radiant energy landing on
it.
That shinny surface must be hotter than the next surface being.
# It would be marginally hotter than its immediate surroundings, in that it
reflected only 95% of teh radiant energy that fell on it. the heat is NOT
so much a source of "radiant heat", but rather "reflected radiant heat."
heated up by the radiant heat it then gives off. OR can you reflect heat
to
another surface without heating the surface doing the reflecting?
# Yes, if you had a surface with 0.0 Emissivity... you would have a 100%
efficient reflector, with no energy absorption.
Then when
measuring that shinny surface using an IR gun it reads low heat but the
surface it reflecting too will read higher heat? Is that possible?
# I did an interesting experiment as follows:
I have a flat mirror on a wall. I have a cheap "Laser Thermometer", which
when pointed to the wall beside the mirror reads
: 45 degree angle: 55 F
90 degree angle 55 F
# When pointed at teh mirror,
45 degree angle 55 F
90 degree angle 56 F
#When pointed at my hand, I read 92 degrees F
When pointed to the mirror, but with the reflected red dot hitting my hand,
I read 60 F
When I remove my hand from the path of teh reflected beam and the red dot
hits teh wall, I read 57
# I conclude that:
1: This cheap "Laser Thermometer is actually very good.
2: It appears to correct for the different emissivities of a mirrored
surface, e=.05, and a wall, e=.9
3: It measures the surface temperature of the mirror, and not the
temperature of teh reflected surface.
4: However, while it "mostly measures the mirror surface, the "reflected
measurement" of my hand temperature was a bit above room temperature.
# Perhaps others will have a different interpertation of my little test?
Best wishes,
Kevin
Thanks
Frank
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Kevin
Sent: Wednesday, March 07, 2012 1:54 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] radiant heat capture, total heat measurement
Dear Frank
----- Original Message -----
From: "Frank Shields" <[email protected]>
To: "'Discussion of biomass cooking stoves'"
<[email protected]>
Sent: Wednesday, March 07, 2012 5:30 PM
Subject: Re: [Stoves] radiant heat capture, total heat measurement
Stovers,
Quick question - does radiant heat require the subject be 'n sight' of
the
object being heated?
"Radiant Heat" is basically the same as "conventional light", in that it
goes in straight lines, but can be reflected. A "low emissivity" surface,
such as polished silver, will reflect "radiant heat" to areas that cannot
"see teh source" directly. (Same as a mirror will reflect light "around
corners.")
Best wishes,
Kevin
Thanks
Frank
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Richard
Stanley
Sent: Wednesday, March 07, 2012 12:27 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] radient heat capture, total heat measurement
Andrew,
Its the old quandry of Brownian movement then, eh ?
Still that "sense we an animals all have of "heat' and "warmth "
remains well beyond degrees of temperature oer se.
Something missing between science and perception that unless clarified
and
quantified would seem to leaves stove performance assessment abit untidy.
Richard Stanley
www.legacyfound.org
=======
On Mar 7, 2012, at 11:44 AM, [email protected] wrote:
On Tue, 6 Mar 2012 07:47:03 -0800, Richard Stanley wrote:
If radient energy is the mother and conductive convective "heats" are
added expressions of it, then why does one rely only upon measurement of
thermal heat only in these more tangible but not necessarily more
influential bands of the spectrum, as the standard measure of cooking
efficiency ?
I suppose it's to do with what means we have of producing the power to do
the cooking, fire is the easiest way of liberating the energy and
transferring it to the cooking pot. Plants have concentrated sunlight
into
wood.
Light can plainly be used for heating, didn't one of the ancient greeks
write of the concentrated beams reflected from polished bronze shield
setting fire to ships rigging?
Micro waves in themselves are not "hot" but they do a wonderful job of
heating by disturbing molecules, just as the visible band of radiation we
call heat, does.
Presumably there was no evolutionary advantage in having an organ that
can
sense infra red in the same way eyes interpret light but many animals do
have increased sense of warmth, snakes can hunt by it.
Microwaves for cooking have only become commonplace in the last 60 years
but the principle is the same as other means of heating, they selectively
excite water molecules. The microwave radiation is tuned to deliver in
frequencies which water molecules will accept in discrete amounts,
otherwise
they would just pass straight through.
My naked supposition is therefore, that beyond a normal thermometer or
one
measuring just IR, one needs a more comprehensive "molecule disturbing"
measurment device
A thermometer is something that reacts to change in temperature, it
doesn't
measure the activity of molecules but rather compares the effect the
molecules have on a substance.
I don't think it is possible to directly measure the state of a molecule
without changing it.
AJH
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