Back Radiation

[sigurdur]

OK....here goes. READ the following link........let's talk about the science of the link.........in a scholarly fashion.

www.stkate.edu/physics/phys100/Chapt7.html

[sigurdur]

iceskater:
Read the whole chapter. It is quit definitive. If you agree with what the chapter indicates, then there is no controversy.

IF there are areas of the chapter that you find at fault, bring them to our attention.

[Andrew]

Here is a simple experiment demonstrating back-radiation

The left hand plate is heated from behind by a light bulb to about 59C.
The wall on the right is around 16.5C
The moveable plate is 30-35C

So the hot plate is analogous to the earths surface

the warm plate is analogous to the earths atmosphere as an absorber/emitter when it is present and as a non-absorber/emitter when it is not there.

The wall is analogous to outer space

[Andrew]

Feb 23, 2012 2:18:21 GMT sigurdur said:

iceskater:
Read the whole chapter. It is quit definitive. If you agree with what the chapter indicates, then there is no controversy.

IF there are areas of the chapter that you find at fault, bring them to our attention.

This text is not sufficiently involved to draw out the nature of the problem I am having with Icefisher. Your text is too complicated and too simple also.

[Andrew]

Sigurdur

I think it would be better if I explain to you what backradiation is if you do not already understand it. It will be much simpler and then you will be in a position to talk to Icefisher if you want to

The problem i am having with icefisher is his understanding of thermodynamic laws where he says backradiation does work for nothing.

Why he says that work is done for nothing is a mystery to me.

Backradiation can only be possible during cooling, where a heated object is continually cooling, or an object that is not heated just cools till it reaches equilibrium

So climate backradiation happens when the earth is rising in temperature, is stable or is cooling and happens regardless of the temperature of the atmosphere

Nothing gets gained for nothing.

So if you ask me questions i can give you answers till we are both satisfied you understand backradiation

[sigurdur]

iceskater:
1. The hot plate analogy does not work.
The warm plate can not be anagolous to the atmosphere. A solid behaves very differently in relation to radiation than a gas does.

Backradiation is continuous for starters. ALL matter is trying to achieve absolute zero, and even if cold, continuously emits radiation. The ONLY equilibrium is when it achieves absolute zero.

[Andrew]

Feb 23, 2012 2:51:37 GMT sigurdur said:

iceskater:
1. The hot plate analogy does not work.
The warm plate can not be anagolous to the atmosphere. A solid behaves very differently in relation to radiation than a gas does.

Backradiation is continuous for starters. ALL matter is trying to achieve absolute zero, and even if cold, continuously emits radiation. The ONLY equilibrium is when it achieves absolute zero.

1. The warm plate can not be anagolous to the atmosphere. A solid behaves very differently in relation to radiation than a gas does.

Why do you think a solid behaves very differently to a gas in relation to radiation? A sufficiently dense gas, or sufficiently long length of gas is opaque to radiation of a certain frequency just as a solid is. There is no essential difference between these two types of matter - you need to explain what you are getting at there.

However, a gas is more transparant to some radiation.

But how does that invalidate the experiment?

The moon for example gives a backradiation effect, as would a cliff face or opposite valley side on earth.

The issue with me and Icefisher is not in any case about solids or gases as far as I have found out so far

2. Backradiation is continuous for starters.

Yes backradiation is continuous. But if the atmosphere did not have an absorbing atmosphere it would not happen at all. That is the demonstration i am making when there is no mid range plate.

3. ALL matter is trying to achieve absolute zero, and even if cold, continuously emits radiation,

You cannot say that all matter is trying to achieve absolute zero. Matter just is, and then absorbs or emits radiation without trying to do anything. Yes, even if cold, matter continuously emits radiation.

4. The ONLY equilibrium is when it achieves absolute zero

Equilibrium can happen at any temperature if the conditions are right

Equilibrium tends to be a theoretical concept. However, if you put a lump of hot metal in space it reaches equilibrium around 4C where there is a balance between the forces of heating and cooling.

-------------------------------------------------------------------------------

the issue between me and Icefisher is one of relative heat and absorption/emission for objects.

He says a colder object cannot emit radiation to be absorbed by a warmer object.

In a nutshell, his theory is that the green house effect only works for a warmer atmosphere and colder surface, so that same temperature or colder atmospheres than the surface are not part of the greenhouse gas effect

[icefisher]

The issue with me and Icefisher is not in any case about solids or gases as far as i have found out so far, he issue is one of temperatures where he says a colder object cannot emit radiation to be absorbed by a warmer object.


The topic you are posting to was posted by me and the premise was that there is no difference between a surface molecule and gas molecule in regards to their radiative properties. Look at the master post.

As usual you have it backwards and you are pursuing the cutting up of strawmen. Go back and read the first post and stop being such a narcissist!

The problem is fundamental properties are wrong in the right hand diagram. The surface molecules are not warming the surface below to a higher temperature than the surface! So the IR-active gases should not either.

Oh so you say! Well the surface is different! It isn't letting shortwave through like CO2 does!

But listen carefully to your own arguments Iceskater!

The emission of IR from molecules is random it has nothing whatsoever to do with the direction of the source of heat!!!!!!

Thus the SW/LW stuff is just total BS and guess what that does! It makes climate science full of BS. It makes backradiation totally irrelevant it sends folks back to the drawing board. Its just pure logical.

Indeed Iceskater you have failed to listen. The entire issue is whether gas has peculiar properties that surface molecules do not with regards to electromatic radiation, if they do I am very interested in reading a study on that.

Sometimes science needs a good dose of logic and philosophy.

[Andrew]

Feb 23, 2012 11:18:24 GMT icefisher said:

The issue with me and Icefisher is not in any case about solids or gases as far as i have found out so far, he issue is one of temperatures where he says a colder object cannot emit radiation to be absorbed by a warmer object.


The topic you are posting to was posted by me and the premise was that there is no difference between a surface molecule and gas molecule in regards to their radiative properties. Look at the master post.

As usual you have it backwards and you are pursuing the cutting up of strawmen. Go back and read the first post and stop being such a narcissist!

The problem is fundamental properties are wrong in the right hand diagram. The surface molecules are not warming the surface below to a higher temperature than the surface! So the IR-active gases should not either.

Oh so you say! Well the surface is different! It isn't letting shortwave through like CO2 does!

But listen carefully to your own arguments Iceskater!

The emission of IR from molecules is random it has nothing whatsoever to do with the direction of the source of heat!!!!!!

Thus the SW/LW stuff is just total BS and guess what that does! It makes climate science full of BS. It makes backradiation totally irrelevant it sends folks back to the drawing board. Its just pure logical.

Indeed Iceskater you have failed to listen. The entire issue is whether gas has peculiar properties that surface molecules do not with regards to electromatic radiation, if they do I am very interested in reading a study on that.

Sometimes science needs a good dose of logic and philosophy.

The moon and terrestial cliff faces, trees, buildings etc are a source of backradiation emitted to the surface of the earth.

There is no difference between a specific gas molecule or a specific solid or liquid molecule for the purposes of backradiation emissions.

The only issue is the position of the molecule that emits the backradiation

Any molecule, placed between the surface and outerspace, that intercepts the surface emissions by absorption, will slow down the surface cooling rate, by sending some of the absorbed energy, now energising that molecule, back to the surface of the Earth as backradiation.

The issue has almost nothing to do with gas molecules, but rather molecules that are between the line of sight of the surface molecules and space.

The surface molecules are not warming the surface below to a higher temperature than the surface! So the IR-active gases should not either.

Correct. In the ordinary sense of the meaning of 'warming' the surface molecules are not warmed by the backradiation.

In the ordinary sense of the word, the surface is warmer because the atmosphere slows the net radiation cooling rate of the surface, where cooling to outerspace has to happen through an absorbing/emitting atmosphere.

The emission of IR from molecules is random it has nothing whatsoever to do with the direction of the source of heat!!!!!!

Correct. The atmosphere randomly emits radiation in all directions regardless of the source of the energy the atmosphere has absorbed. However, without the heat of the earths surface the atmosphere would have relatively little ability to cause significant emission of IR towards the surface of the Earth

Thus the SW/LW stuff is just total BS

If you set aside Solar heating for a moment:

The Earth has internal heat sufficient to last billions of years even if the sun totally failed. Even if the atmosphere that remained after such a failure, was very thin, and extraordinaryly cold, the heat emitted by the surface of the earth would have to pass thru an absorbing and emitting atmosphere, so the net heat loss rate of whatever molecule was on the surface would be reduced.

Something approximately similar happens on many nights of the year, plus at some altitudes the air is always very much colder than the surface day or night no matter what time of the year.

Therefore day or night, the net heat loss rate of the surface is reduced by backradiation regardless of the temperature of the atmosphere

Indeed Iceskater you have failed to listen. The entire issue is whether gas has peculiar properties that surface molecules do not with regards to electromatic radiation, if they do I am very interested in reading a study on that.

As i have explained here, the issue is nothing to do with the state of the molecule, but rather the spectral properties and the position of the absorbing molecule that sits between space and the surface emission.

Sometimes science needs a good dose of logic and philosophy.

Science always needs good experimental work to ensure what we think of being as good logic or philosophy is grounded by something more than what can be created in the mind.

For example we can theorise that the faces of the moon and earth that face each other will be warmer than the rest of their surfaces

And we can test that very easily with a simple experiment.

[icefisher]

The problem is fundamental properties are wrong in the right hand diagram.

1) The surface molecules are not warming the surface below to a higher temperature than the surface!

You said this was true


2) So the IR-active gases should not either.

You said this was true

3) Oh so you say! Well the surface is different! It isn't letting shortwave through like CO2 does!
But listen carefully to your own arguments Iceskater!

The emission of IR from molecules is random it has nothing whatsoever to do with the direction of the source of heat!!!!!!

You said this was true

The only reservation you expressed was a slowing of cooling:

However, without the heat of the earths surface the atmosphere would have relatively little ability to cause significant emission of IR towards the surface of the Earth

Its my contention you cannot claim a slowing of cooling by randomly emitting photons as a corollary to the premises you accept above.

Let me set the stage a little neater to explore that so we don't get into an argument about obfuscation.

First lets try to agree on one additonal premise:

1. SB equations for the blackbody radiation of an object some distance from the sun are based upon an input of radiation from the disk of the sun considering radiation from only one side of the disk.

Seems like a no brainer but it should be specified anyway. It really doesn't change anything but I think its part of the confusion so I wanted to specify this. The emission rates are by square meter so they emissions on the backside of the solar disk are the same as on the front side.

So:

If you take a blackbody ball (ball A) in a 0K environment with a constant heat source it will be receiving and emitting radiation at a constant rate so that cooling equals heating. Lets say this ball equilibrates at 100K so the heat input from the core of the disk are steady resulting in about 5.67watts/m2 cooling from all surfaces.

Now we are going to take another blackbody ball (B) and place it near A.

B is 0K at start and has no energy.

It also has no internal or external heat source. It is going to obtain an external heat source by placing it near A but thats all it will have for a source of heat.

So it begins warming in the presence of A.

I am going to introduce another premise here for B. Lets also specify that this ball has zero heat content capability. So that there is no effect from conduction through the ball restricting the path of heat through the ball (we are doing this purely radiatively like climate science does it supposedly).

So the result of this is B warms instantaneously on all surfaces to the same temperature as A including the back surface of B

Since the disk on ball B that is backside from A is the same size as the receiving side its going to be radiating 5.67watts (just like in the left hand surface diagram at the top of this topic).

As a result of this there would be zero slowing of radiation from A.

Do you agree with that?

Lets dispense with the notion of absorption as a vehicle for slowing the cooling of the surface.

The presence of the second ball would be a complete non issue to the first ball. the second ball would heat instantaneously and be emitting everything it did not pass through due to transparency by emissions out its back side. This would also be the case for a perfect conductor even if the ball had heat capacity.

Now that is only the case for a blackbody ball B.

Likely for a substance to exist that is a blackbody it would have to have conductivity adequate to instantly transfer heat through the body at the same rate it absorbs it.

But we have introduced the notions of conductivity and heat capacity here and as such I have problems with the approach of climate science in cherry picking what heat capacity, conductivity and what convection they are going to use in their warming model. Look up radiation has to be included in the model as well in addition to look down and it has to start with the effects of all this on solar incoming as well as I see that as the door closing on the greenhouse effect as radiation is exposed as a zero sum game. . . .namely unless otherwise modified its seeking that SB number.

[magellan]

The setup:
1) Cooper-Atkins 3 channel thermometer w/1075 puncture probes
2) 2-Fluke 87v DMM w/80BK-A contact bead probe
3) 2- ~.67" thick x 3.67" dia. steel disks. All face surfaces have been ground to ~32 micro finish.

I have other temperature monitoring equipment but they are in the field. One more Fluke bead probe should be available in a few days. An IR thermometer is inappropriate for these types of tests because the emissivity differences of surfaces and slight variation in angle toward the part (especially cylindrical) will cause inaccurate readings. Handheld IR thermometers aren't really that great to begin with if true readings are important.

In the picture, the two specimens (T1 & T2) are identical in material, size and mass. One hole is drilled through the center of each for the puncture probes. Being immersion probes they cannot be used to contact the part using the tips.

Keep in mind this is only a preliminary test so that it can be improved on.

Initial conditions: all equipment and parts were allowed to soak for 24 hours in ambient room temperature- 68-72 F. Temperature variation between the 4 probes did not exceed .6 F prior to heating the T2 specimen.

Specimen T2 was heated in an industrial oven for 1 hour 15 minutes to achieve 175 deg F. Specimen T1 was left as is in the photo. Once removed from the oven, T2 was immediately placed on T2_A probe and placed into position ~.020" (.5mm) away from T1. The gap did not vary more than .010" (.25mm).

The results shown in the photo are after ~12 minutes. It was not timed. The "hot" part (T2) temperature did not warm any more at the gap end than the open end. Iceskater said the warmer part would be warmed further by the colder part during the cooling process. I'm open for explanations for why this did not occur, and the heat transfer equations that disagree with my observations.

T2 is on the left. T1 on the right.





P.S. I have a temp probe calibrator to validate accuracy of the measurements.

[Andrew]

Feb 23, 2012 21:08:23 GMT icefisher said:

The problem is fundamental properties are wrong in the right hand diagram.

1) The surface molecules are not warming the surface below to a higher temperature than the surface!

You said this was true

I commented only upon the part not struck thru.

2) So the IR-active gases should not either.

You said this was true

I did allowing for my comment above

3) Oh so you say! Well the surface is different! It isn't letting shortwave through like CO2 does!
But listen carefully to your own arguments Iceskater!

The emission of IR from molecules is random it has nothing whatsoever to do with the direction of the source of heat!!!!!!

You said this was true

I commented on only the part not struck thru.

The only reservation you expressed was a slowing of cooling:

Obviously you have changed what i said quite substantially because you have left out the most significant part of what i said.

However, without the heat of the earths surface the atmosphere would have relatively little ability to cause significant emission of IR towards the surface of the Earth

Its my contention you cannot claim a slowing of cooling by randomly emitting photons as a corollary to the premises you accept above.

There is no slowing of random processes

So you are claiming I am saying something I am not saying

Let me set the stage a little neater to explore that so we don't get into an argument about obfuscation.

First lets try to agree on one additonal premise:

1. SB equations for the blackbody radiation of an object some distance from the sun are based upon an input of radiation from the disk of the sun considering radiation from only one side of the disk.

Seems like a no brainer but it should be specified anyway. It really doesn't change anything but I think its part of the confusion so I wanted to specify this. The emission rates are by square meter so they emissions on the backside of the solar disk are the same as on the front side.

So:

If you take a blackbody ball (ball A) in a 0K environment with a constant heat source it will be receiving and emitting radiation at a constant rate so that cooling equals heating. Lets say this ball equilibrates at 100K so the heat input from the core of the disk are steady resulting in about 5.67watts/m2 cooling from all surfaces.

Now we are going to take another blackbody ball (B) and place it near A.

B is 0K at start and has no energy.

It also has no internal or external heat source. It is going to obtain an external heat source by placing it near A but thats all it will have for a source of heat.

So it begins warming in the presence of A.

I am going to introduce another premise here for B. Lets also specify that this ball has zero heat content capability. So that there is no effect from conduction through the ball restricting the path of heat through the ball (we are doing this purely radiatively like climate science does it supposedly).

So the result of this is B warms instantaneously on all surfaces to the same temperature as A including the back surface of B

Since the disk on ball B that is backside from A is the same size as the receiving side its going to be radiating 5.67watts (just like in the left hand surface diagram at the top of this topic).

As a result of this there would be zero slowing of radiation from A.

Do you agree with that?

Lets dispense with the notion of absorption as a vehicle for slowing the cooling of the surface.

The presence of the second ball would be a complete non issue to the first ball. the second ball would heat instantaneously and be emitting everything it did not pass through due to transparency by emissions out its back side. This would also be the case for a perfect conductor even if the ball had heat capacity.

Now that is only the case for a blackbody ball B.

Likely for a substance to exist that is a blackbody it would have to have conductivity adequate to instantly transfer heat through the body at the same rate it absorbs it.

But we have introduced the notions of conductivity and heat capacity here and as such I have problems with the approach of climate science in cherry picking what heat capacity, conductivity and what convection they are going to use in their warming model. Look up radiation has to be included in the model as well in addition to look down and it has to start with the effects of all this on solar incoming as well as I see that as the door closing on the greenhouse effect as radiation is exposed as a zero sum game. . . .namely unless otherwise modified its seeking that SB number.

You are transmogrifying what i said. Note the yellow additions above.

Importantly you left out the part that you refuse to look at after all of these weeks of struggle on my part.

You left out:

In the ordinary sense of the meaning of 'warming' the surface molecules are not warmed by the backradiation.

In the ordinary sense of the word, the surface is warmer because the atmosphere slows the net radiation cooling rate of the surface, where cooling to outerspace has to happen through an absorbing/emitting atmosphere.

Then you say

1. Its my contention you cannot claim a slowing of cooling by randomly emitting photons

I am not claiming any such thing



The fundamental rate of random processes remains the same.

The net radiation cooling rate changes

As others have pointed out you should be able to understand a net loss rate in financial terms when income can be relatively massive and yet losses are larger.

And you should be able to understand a net profit when there are very large losses

The Earths radiation budget is just accounting for what comes in and what goes out, the whole thing is numerically exactly like accounting.

The Greenhouse effect is like the Earth employing shop workers who spend their income in the shop. If the Earth decides to employ people on Mars and they spend their money there, the Earth gets less income returning than Mars sends elsewhere.

Nobody claims that having employees in a shop who spend money in the shop is going to make you rich via that income alone. It can only make you poorer no matter where they are based.

The earth either has a profit or a loss in the radiation budget.

Greenhouse gases only reduce losses by cooling the atmosphere.

And the only way to get rid of the heat that is not emitted to space is by increasing emissivity at the surface or increasing the temperature. The sun heats the earth till it is hotter.

However, my expression net radiation cooling rate is probably the wrong thing to say.

---------------------------------------------------------------------------

2. Your thought experiment

i. Because of the way you have described your thought experiment you cannot say:

Lets say this ball equilibrates at 100K

As described the ball is externally heated by a heat source that is only in one sector of the zero K surrounding. There is therefore a temperature gradient across the ball from the hot side to the cold side. Surface temperatures are different at different points of the surface. The ball is not in equilibrium. The temperatures might be stable however.

ii. You need to rework the idea of absence of heat capacity

If an object has no heat capacity then it cannot have a temperature. Instead you need to consider an object that has very little heat capacity so that the amount is approaching an infintessimally small heat capacity

Alternatively just say, consider a very low amount of conduction or an infintessimally small conduction.

iii. So the result of this is B warms instantaneously on all surfaces to the same temperature as A including the back surface of B

Since B is now built from something that is more real, and is cooling like a real object, the back surface of B is cooler than the heated front surface of B.

iv. As a result of this there would be zero slowing of radiation from A

Just to emphasie the point i made in the very first part 1. in this reply, The temperature of surroundings has no ability to slow the random photonic emissions coming from a body with a given emissivity and given temperature.

The only way to reduce the radiation coming from A is to lower the emissivity or lower the temperature of A.

But this can be achieved by design entirely from outside A

If Body B near Body A, wishes to reduce the emissions coming from A then it needs to do something on B that alters the temperature of A. For example mirrors on B to redirect emissions from A away from B and away from A, so that B is cooler and emits less radiation to A, and A is therefore cooler.

[Andrew]

Feb 24, 2012 0:31:58 GMT magellan said:

Iceskater said the warmer part would be warmed further by the colder part during the cooling process. I'm open for explanations for why this did not occur

Magellan

Here are my initial observations and a diagram of what i am expecting to see.

1. I think though, you have fundamentally misunderstood the experiment you have to construct or what you are looking for?

But can you in any case clarify what the voltmeter probes are measuring please? Is it a surface temperature or deeper in the metal? Do you have data for all 4 of the voltmeter probe holes?

2. You said: Iceskater said the warmer part would be warmed further by the colder part during the cooling process

What I said or at least was doing my best to convey when it is not so easy to put into words was:

When the warm object 1, is cooling, 1 will be warmer on the surface where it is near a cooler object 2 , where otherwise/elsewhere, 1 will be exposed to the fewer emissions coming from a very much colder surface 3. So three surfaces were involved of 1 = Warm, 2 = cooler and 3 = very cold.

Your arrangement does satisfy that condition once the room temperature block has warmed up. So no problem apart from what you might expect to see from this experiment.

3. However, you have a tiny air gap of 0.25mm between the metal where air is a very poor conductor other than when tiny air gaps are involved. There is therefore an extra stronger cooling route than on the other side of the preheated piece of metal. The stronger cooling route will exist between hot metal and cold metal via a tiny and therefore relatively good conducting air gap. The result will be the temperature gradient from the hot center will be a much higher slope of declining temperatures than expected.

Why did you chose such a tiny air gap?

Also since you are not doing this in a vacuum and convection/conduction of air are present it might be better to reduce the temperatures rather than have them so relatively higher than the environment, otherwise between the two blocks you will have a greater convective current.

I found it very easily worked for a 59C plate for my particular arrangement - wall at 16.5C, warm plate at 30/35 and heated plate at 59C

The same principles are involved.

[magellan]

Feb 24, 2012 6:44:15 GMT Andrew said:

Feb 24, 2012 0:31:58 GMT magellan said:

Iceskater said the warmer part would be warmed further by the colder part during the cooling process. I'm open for explanations for why this did not occur

Magellan

Here are my initial observations and a diagram of what i am expecting to see. From your text and pictures i am not sure what all 4 of your temperatures are.

If you have something like:

T2B 119.0
T2A 127.1
T1A 126.0
T1B 116.8

those are the expected results.

1. I think though, you have fundamentally misunderstood the experiment you have to construct or what you are looking for?

2. You said: Iceskater said the warmer part would be warmed further by the colder part during the cooling process

What I said or at least was doing my best to convey when it is not so easy to put into words was:

When the warm object 1, is cooling, 1 will be warmer on the surface where it is near a cooler object 2 , where otherwise/elsewhere, 1 will be exposed to the fewer emissions coming from a very much colder surface 3. So three surfaces were involved of 1 = Warm, 2 = cooler and 3 = very cold.

Your arrangement does satisfy that condition once the room temperature block has warmed up. So no problem apart from what you might expect to see from this experiment.

3. However, you have a tiny air gap of 0.25mm between the metal where air is a very poor conductor other than when tiny air gaps are involved. There is therefore an extra stronger cooling route than on the other side of the preheated piece of metal. The stronger cooling route will exist between hot metal and cold metal via a tiny and therefore relatively good conducting air gap. The result will be the temperature gradient from the hot center will be a much higher slope of declining temperatures than expected.

Why did you chose such a tiny air gap?

Also since you are not doing this in a vacuum and convection/conduction of air are present it might be better to reduce the temperatures rather than have them so relatively higher than the environment, otherwise between the two blocks you will have a greater convective current.

I found it very easily worked for a 59C plate for my particular arrangement - wall at 16.5C, warm plate at 30/35 and heated plate at 59C

The same principles are involved.

Why did you chose such a tiny air gap?

At what gap do you consider it to be radiation versus conduction? Should I run the test with the parts contacting? Hmm, I've already done that. What do you suppose should happen? Those are rhetorical questions, not 20 questions.

Also since you are not doing this in a vacuum and convection/conduction of air are present it might be better to reduce the temperatures rather than have them so relatively higher than the environment, otherwise between the two blocks you will have a greater convective current.

In vacuum it won't make a hill of beans difference. I'm sure Dr. Spencer would agree. No problem though, we can let it cool to ambient temperature, where at some unspecified moment in time the T1B should diverge from T2B.

NOTE: T1B should actually be T2C, but one my Fluke meters were taken, so the test is minus one bead probe. I neglected to change the sticker on the meter and by the time I noticed, I had already posted.

From your text and pictures i am not sure what all 4 of your temperatures are.

The center probes are references; not very informative without adding more at the outer face, but as I said immersion probes cannot be used as contact probes. Only two matter in this discussion; the two Fluke bead probes at the gap and outer edge. It is at the gap you have insisted would get warmer than the exposed face. Are you changing your story now?

I found it very easily worked for a 59C plate for my particular arrangement - wall at 16.5C, warm plate at 30/35 and heated plate at 59C

What was your procedure? Equipment list? Stated accuracy? Calibrated? No offense, but your "experiment" would not exactly qualify at the school science fair. It isn't even clear what you were conveying in the video.

The equipment I'm using is calibrated. The long probes through the center of the parts have a stated accuracy of +/- .3C. The Fluke bead probes 2.2C FS.

I have the added advantage of narrowing it down with the use of a temperature calibrator. Looks good to me.





So, rather than introducing all sorts of new added caveats, let's stick with what you originally argued. I will repeat the test but will be more procedural. The closer the parts are together, the greater the heat transfer and better resolution. Tell you what, this time I'll do it at .125". Would that suffice?

I can also do it with the parts in full contact. Do you still think it will get warmer at the contact area?

This doesn't need to be any more complicated than what I've already done.

Here are my initial observations and a diagram of what i am expecting to see. From your text and pictures i am not sure what all 4 of your temperatures are.

If you have something like:

T2B 119.0
T2A 127.1
T1A 126.0
T1B 116.8

those are the expected results.

Uh, no. Your expected results were that T1B > T2B. More specifically, the rate of cooling should be slower at T1B. I observed no such thing.

[Andrew]

Feb 24, 2012 18:19:59 GMT magellan said:

Feb 24, 2012 6:44:15 GMT Andrew said:

Magellan

Here are my initial observations and a diagram of what i am expecting to see. From your text and pictures i am not sure what all 4 of your temperatures are.

If you have something like:

T2B 119.0
T2A 127.1
T1A 126.0
T1B 116.8

those are the expected results.

1. I think though, you have fundamentally misunderstood the experiment you have to construct or what you are looking for?

2. You said: Iceskater said the warmer part would be warmed further by the colder part during the cooling process

What I said or at least was doing my best to convey when it is not so easy to put into words was:

When the warm object 1, is cooling, 1 will be warmer on the surface where it is near a cooler object 2 , where otherwise/elsewhere, 1 will be exposed to the fewer emissions coming from a very much colder surface 3. So three surfaces were involved of 1 = Warm, 2 = cooler and 3 = very cold.

Your arrangement does satisfy that condition once the room temperature block has warmed up. So no problem apart from what you might expect to see from this experiment.

3. However, you have a tiny air gap of 0.25mm between the metal where air is a very poor conductor other than when tiny air gaps are involved. There is therefore an extra stronger cooling route than on the other side of the preheated piece of metal. The stronger cooling route will exist between hot metal and cold metal via a tiny and therefore relatively good conducting air gap. The result will be the temperature gradient from the hot center will be a much higher slope of declining temperatures than expected.

Why did you chose such a tiny air gap?

Also since you are not doing this in a vacuum and convection/conduction of air are present it might be better to reduce the temperatures rather than have them so relatively higher than the environment, otherwise between the two blocks you will have a greater convective current.

I found it very easily worked for a 59C plate for my particular arrangement - wall at 16.5C, warm plate at 30/35 and heated plate at 59C

The same principles are involved.

Why did you chose such a tiny air gap?

At what gap do you consider it to be radiation versus conduction? Should I run the test with the parts contacting? Hmm, I've already done that. What do you suppose should happen? Those are rhetorical questions, not 20 questions.

Also since you are not doing this in a vacuum and convection/conduction of air are present it might be better to reduce the temperatures rather than have them so relatively higher than the environment, otherwise between the two blocks you will have a greater convective current.

In vacuum it won't make a hill of beans difference. I'm sure Dr. Spencer would agree. No problem though, we can let it cool to ambient temperature, where at some unspecified moment in time the T1B should diverge from T2B.

NOTE: T1B should actually be T2C, but one my Fluke meters were taken, so the test is minus one bead probe. I neglected to change the sticker on the meter and by the time I noticed, I had already posted.

From your text and pictures i am not sure what all 4 of your temperatures are.

The center probes are references; not very informative without adding more at the outer face, but as I said immersion probes cannot be used as contact probes. Only two matter in this discussion; the two Fluke bead probes at the gap and outer edge. It is at the gap you have insisted would get warmer than the exposed face. Are you changing your story now?

I found it very easily worked for a 59C plate for my particular arrangement - wall at 16.5C, warm plate at 30/35 and heated plate at 59C

What was your procedure? Equipment list? Stated accuracy? Calibrated? No offense, but your "experiment" would not exactly qualify at the school science fair. It isn't even clear what you were conveying in the video.

The equipment I'm using is calibrated. The long probes through the center of the parts have a stated accuracy of +/- .3C. The Fluke bead probes 2.2C FS.

I have the added advantage of narrowing it down with the use of a temperature calibrator. Looks good to me.





So, rather than introducing all sorts of new added caveats, let's stick with what you originally argued. I will repeat the test but will be more procedural. The closer the parts are together, the greater the heat transfer and better resolution. Tell you what, this time I'll do it at .125". Would that suffice?

I can also do it with the parts in full contact. Do you still think it will get warmer at the contact area?

This doesn't need to be any more complicated than what I've already done.

Here are my initial observations and a diagram of what i am expecting to see. From your text and pictures i am not sure what all 4 of your temperatures are.

If you have something like:

T2B 119.0
T2A 127.1
T1A 126.0
T1B 116.8

those are the expected results.

Uh, no. Your expected results were that T1B > T2B. More specifically, the rate of cooling should be slower at T1B. I observed no such thing.

Magellan

I am a bit confused

I pointed out that i am not sure if you know what experiment you should be working to build. You have not said anything about that.

Are you saying you tried this experiment at for example 30CM spacings and then progressively moved it to 0.25mm?

I am saying it makes a difference in air and having the metal so close together needs to be explained. What is the reason for having them so close together?

Why are suggesting moving them even closer or having them touching???

You say it makes no difference at all that the experiment is done in air. We have a point of difference and i cannot understand why you would suggest the metal touches.

when i listed those temperatures of

T2B 119.0
T2A 127.1
T1A 126.0
T1B 116.8


I was thinking this described something like the left to right measurements you found. Only later did i realise that 119 and 116.8 were the first and second temperatures from left to right.

So results wise i have a problem, or alternatively I am still confused as to where you are measuring your temperatures.

Presumably the black equipment is measuring the inner faces of the metal? What are the temperatures please. Presumably 120 is one of those temperatures? but which one and where is the other?

What are the drillings on the side of the metal? Where do they go? depth and so forth

And at the moment i am wondering about the air gap

Thats about it for now

Once I understand what you have built and what the results are, and I know why you are suggesting moving the metal closer, then i can comment more.