[Stoves] radiant heat capture, total heat measurement

Wed Mar 7 22:32:25 CST 2012

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" <frank at compostlab.com>
To: "'Discussion of biomass cooking stoves'" 
<stoves at lists.bioenergylists.org>
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: stoves-bounces at lists.bioenergylists.org
> [mailto:stoves-bounces at lists.bioenergylists.org] 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" <frank at compostlab.com>
> To: "'Discussion of biomass cooking stoves'"
> <stoves at lists.bioenergylists.org>
> 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: stoves-bounces at lists.bioenergylists.org
>> [mailto:stoves-bounces at lists.bioenergylists.org] 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, ajheggie at gmail.com 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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