Date: Tue Feb 6 18:05:59 2007

Author: Bernard Cleyet

Subject: Re: CO2 demo (was) List conversations. Please Read.


I think your supposition is correct.

Often ignored: Water is a "better" absorber than CO2. Have you tried
using saturated air?

I couldn't decode FLIR thinking it was a spectral region. They make
many cameras and the one you have evidently doesn't depend on the
regions of strong CO2 absorption. At least one of their cameras does
use a water absorption region as they tout its use in detecting water in
their advert.

A very handy IR manual is the military one. An old one (1965) probably
answers this. p. 228 gives the solar spectrum and its dissection *.
CO2 absorption is mainly by two not very broad bands centred near 2.8
and 4.3 micron (and beyond 13) While H2O is characterized by two broad
windows centred aprox. at 4 and 10, and about 2 and 5 microns wide
(respectively) . There are three narrow ones below 2.4. So, if your
camera is a medium IR one, it's not surprising CO2 doesn't do much.
Absorption by H2O vapour will confirm this supposition. Note a camera
sensitive around ten microns is most efficient for to imaging mammals, etc.

* Rather low resolution graphs; high ones later in the chapter.

bc, plays w/ that system and the hugh CO2 filled balloon upstairs.

p.s. The cold air balloon contained more water? How did you inflate
the cold one. That breath is rather wet probably shoots down my
theory. Have you tried a wax block? It supposedly has windows in the
IR. I've been waiting for the Sun (I knew what the Beetles were singing
when I lived in England!) to try out my large wax lens.

p.p.s Cu mirror, yes expected as a good conductor -- Drude theory.
Was it free of oxide? A BTW, The emissivity of Cu oxide is rather high
while Cu polished very low ~ 0.88 and 0.02 respectively (8 => 14 micron).

Paul Doherty wrote:

> Hi Wolfgang
> What camera are you using?
> And for the rest of you tappers.
> We use a FLIR type camera at the Exploratorium.
> I don't see any difference with an air filled versus a CO2 filled
> balloon.
> I even took a 15 cm diameter 1 meter long PVC pipe, covered the ends
> with saran wrap and filled it with CO2 to get more path length and
> still saw no visible absorption.
> I wonder if there is enough IR coming through the band of wavelengths
> in the infrared between the two absorption bands of CO2 and if IR
> FLIR cameras are designed to see through CO2?
> We do see a difference with balloons full of cold air which are
> opaque and balloons full or warm air (breath inflated) which are
> transparent.
> If you have a FLIR camera note that clear acrylic is black opaque.
> Brown plastic trashbags are opaque in the visible and somewhat
> transparent in the IR.
> a second surface mirror is black with the IR yet the copper bottom of
> a Revereware frypan is a great IR mirror (or just a sheet of copper)
> And you must take a beaker of hot water which glows white
> and a beaker of cold water which is black
> and then pour the white liquid into the black while watching on the
> IR camera
> Here is our You Tube Video as part of our global climate change
> webcast which shows several of these activities.
> (Note behind Stephanie's head there are three mirrors, the two black
> ones are actually mirrors in real life while the one that looks like
> a mirror in IR is actually a sheet of copper.)
> Paul Doherty
> On Feb 6, 2007, at 9:44 AM, Wolfgang Rueckner wrote:
>> We do something similar, except with balloons. An air-filled
>> balloon is completely transparent whereas a CO2-filled balloon is
>> opaque. -- Wolfgang
>> On Feb 6, 2007, at 12:04 PM, Rick Tarara wrote:
>>> There is a demo used in the PBS film 'What's up with the weather'
>>> that looks effective but requires some specialized equipment. They
>>> use a chamber with clear end plates through which an infrared TV
>>> camera can view. They put a person on the far side of the chamber
>>> and get a head shot through the infrared camera with the chamber
>>> filled with normal air. Then they flood the chamber with CO2 and
>>> the image quickly starts to fade, ultimately to disappear. This
>>> clearly indicates that the CO2 is absorbing the IR.
>>> I have no idea about the cost of such a setup.
>>> Rick
>>> ***************************
>>> Richard W. Tarara
>>> Professor of Physics
>>> Saint Mary's College
>>> Notre Dame, IN
>>> ******************************
>>> Free Physics Software
>>> PC & Mac
>>> *******************************
>>> ----- Original Message ----- From: "Urs Lauterburg"
>>> To:
>>> Sent: Tuesday, February 06, 2007 11:42 AM
>>> Subject: Re: [tap-l] List conversations. Please Read.
>>>> Michael,
>>>> Your judgement is correct. I tried the original setup with Argon
>>>> and got the same behavior as with CO2. Convection was inhibited
>>>> which caused most of the heating. Lower convection of course
>>>> influences thermal conditions a lot.
>>>> I am however working on a demo which will show how CO2 absorbs a
>>>> certain range of infrared radiation. However, the real challenge
>>>> is to make it simple and straight forward. Not the effect I mean
>>>> but how it's best brought to the minds of our pupils.
>>>> Thank you for pitching in your estimate and regards
>>>> Urs
>>>> Urs Lauterburg
>>>> Physics demonstrator
>>>> Physikalisches Institut
>>>> University of Bern
>>>> Switzerland
>>>>> Urs,
>>>>> I'm guessing convection was inhibited by minimal mixing between
>>>>> the pure CO2
>>>>> layer and the air above it. You created a greenhouse without any
>>>>> glass on
>>>>> top?
>>>>> Michael Thomason
>>>>> Director of Physics Learning Laboratories
>>>>> University of Colorado Boulder Department of Physics
>>>>> 303-492-7117
>>>>> -----Original Message-----
>>>>> From: [mailto:tap-l-
>>>>>] On
>>>>> Behalf Of Urs Lauterburg
>>>>> Sent: Monday, February 05, 2007 2:10 PM
>>>>> To:
>>>>> Subject: Re: [tap-l] List conversations. Please Read.
>>>>> Dear Tap-lers,
>>>>> I very much second what Jerry said. After all, there always have
>>>>> been
>>>>> relations between physics, the world, religion and politics and it's
>>>>> the broader content of things which make certain aspects more
>>>>> relevant than others.
>>>>> Of course the list is primarily targeted at creating and maintaining
>>>>> educational hardware for physics education but since we often deal
>>>>> with young people, who are for good reasons concerned about the ways
>>>>> our planet is treated by mankind it's also important to exchange
>>>>> ideas about hot topics through the list. Global warming is hot and
>>>>> involves a lot of physics too.
>>>>> A few months back I posted a contribution to tap-l about a
>>>>> demonstration experiment that showed the greenhouse effect
>>>>> produced by CO2. The setup was strikingly simple. I had an infrared
>>>>> light bulb shine into a glass, rectangular aquarium shaped container
>>>>> which was open on the top. At the bottom on piece of plywood I
>>>>> hade a
>>>>> thermal sensor to measure the temperature at equilibrium. Now after
>>>>> filing the container with CO2 it soon led to a considerable
>>>>> temperature increase of about 2 to 3 degrees Celsius.
>>>>> Now just recently when wanting to show this rather impressive demo
>>>>> again I discovered that we measured another effect. The largest part
>>>>> of the temperature raise was not caused by the absorption of
>>>>> infrared
>>>>> by the CO2 as is the case with the REAL greenhouse effect. I
>>>>> leave it
>>>>> up to you physics professionals to make a guess. Maybe some others
>>>>> have already discovered the true reason for the heating in my
>>>>> case in
>>>>> the first place but have politely retained from letting me know back
>>>>> then. This of course would have been a wrong form of politeness.
>>>>> Now, I am still thinking about a nice and simple demo to show the
>>>>> energy absorption of greenhouse gasses and I'm right now tampering
>>>>> with some other more promising setup. However this time I will only
>>>>> make public comments when I am dead (well almost dead) sure that it
>>>>> shows the correct physics.
>>>>> Anyway, have fun guessing what it is that caused the greenhouse
>>>>> effect in my aquarium !
>>>>> Thank you for the lively and polite discussion and for caring about
>>>>> the subject by looking at the actual facts caused by the present, to
>>>>> some extent man-made and altered composition of the earth's
>>>>> atmosphere.
>>>>> Urs
>>>>> Urs Lauterburg
>>>>> Physics demonstrator
>>>>> Physikalisches Institut
>>>>> University of Bern
>>>>> Switzerland