tisdag 25 oktober 2011

Radiative Heat Transfer: History

Pictet's experiment

Radiative heat transfer is described in two different ways, as:
  1. One-way net transfer from hot to cold.
  2. Two-way transfer between hot and cold with net transfer from hot to cold.
I argue that 1. is physical obeying the 2nd law of thermodynamics, while 2. is unphysical violating the 2nd law.

The origin of 1. and 2. is traced in The Laws of Radiation and Absorption and Pictet's Experiment back to

1. Pictet:
  • two-way wave theory
  • one-way transfer of heat energy from hot to cold.
2. Rumford (Benjamin Thompson):
  • wave theory
  • radiant heat as an analog to sound
  • higher frequencies excite lower frequencies: heating.
3. Prevost:
  • particle theory, corpuscular fluid caloric
  • matter of heat or fire
  • quanta of energy
  • two-way transfer with hot winning over cold.

The difference between 1. + 2. and 3 is expressed clearly in different views on the case with two bodies of equal temperature:
  • Pictet/Rumford: no exchange of heat energy because of a "balance of power" as standing wave.
  • Prevost: exchange of equal quanta of energy.
The difference can also be seen in the experiment by Pictet illustrated above, with an object and a thermometer placed in the foci of two concave mirrors:

Pictet observed that if the body was chilled by ice, then the thermometer initially at room temperature showed cooling, as if coldness or cold was transferred from the ice to the thermometer. If the body or thermometer was out of focus nothing happened, apparently because the radiative contact disappeared.

The experiment was initially met with surprise suggesting an exchange of something like "quanta of cold" transferred by "frigorific rays" as an analog to exchange of quanta of heat
by a stream of photons.

Pictet gave the natural explanation based on 1. that what happens is that the warm thermometer heats the ice and thus looses heat showing cooling.

Prevost gave a different explanation based on 2. as an imbalance of exchange of "fire particles"
with the effect that the warmer thermometer loses more particles than it receives and thus cools off.

Notice that 3. is similar to the phlogiston theory about a fire-like element released during combustion. Phlogiston theory is no longer part of science, but surprisingly 2. has survived with support of the idea of radiative heat transfer as streams of energy quanta or photons coming from quantum mechanics.

3. thus represents a strange mix of old phlogiston theory and modern physics, and this mix is used by CO2 alarmists to sell the idea of DLR/backradiation.

It is now time to once and for all finish the debate between 1. + 2. and 3. and put 3. into the wardrobe together with phlogiston theory.

3. violates the 2nd law by allowing transfer of heat from cold to warm and 2. serves no other role than supporting CO2 alarmism.

27 kommentarer:

  1. 2. violates the 2nd law by allowing transfer of heat from cold to warm

    Well, it was shown in an earlier comment in your post entitled The Faustian Deal of DLR/Backradiation by Planck that a violation of the second law isn't guaranteed by that kind of a process.

    2. serves no other role than supporting CO2 alarmism.

    Check any standard textbook in heat transfer (for instance Incropera et. al. Fundamentals of mass and heat transfer) and you will see that the active field working on heat and mass transfer do support a view where heat is two way (but of course with a net flow from hot to cold, otherwise the second law would be violated).


  2. By the way, you shouldn't refer to Pictet because he died in 1825 so we can't really ask him what he meant with his experiment. ;-)


  3. It looks like you decided to censor my comment about the fact that your theory has been demonstrated to be unphysical in an earlier discussion on this blog.

    You complain that other censor you, and then you censor others...

  4. I censor comments which are only nasty and nothing else. I do not censor comments with scientific message.

  5. Claes wrote:
    3. violates the 2nd law by allowing transfer of heat from cold to warm

    Can you please show that this really is the case, I mean that a net two-way heat transfer really violates the 2:nd law. And then not just in words, but with equations.


    ps. This is a $\LaTeX$ test ds.

  6. What are the equations for two-way heat transfer?
    Transfer from cold to hot violates the 2nd law. If you speak about two-way transfer, then you speak about two independent transfers, and one of them is from cold to hot in violation of the 2nd law.

  7. Claes wrote:
    Transfer from cold to hot violates the 2nd law. If you speak about two-way transfer, then you speak about two independent transfers, and one of them is from cold to hot in violation of the 2nd law.

    Ok, maybe we talk past each other, let me refine my question.

    Can you explicitly write the 2:nd law in a mathematical form that shows that you can't use the net quantity in a two-way flow as the gauge for the direction of heat? Is my question clearer now?


  8. There is no form of the 2nd law describing two-way flow with net flow from
    hot to cold. Flow from cold to hot is unstable and as such is unphysical. You
    cannot describe in physical terms what is unphysical. Thus there is no physical
    description of two-way heat transfer.

  9. Pictets experiment supports the global warming idea

    1. A Heated object is colder when exposed to a source of cold

    2. The heated object becomes warmer when the source of cold becomes warmer. Ie as the ice becomes water and the water warms the thermometer warms.

  10. None of 1 or 2 involves transfer of heat energy from cold to warm.

  11. Well of course not.

    Are you disputing the Earth that the Earth would be colder if heat was lost directly to outerspace?

    I am supposing not. Because the Earth is a heated object and it is not exposed to the coldness of space it is warmer.

    please read my original comment again
    If the transfer of heat was directly to space the Earth wobservation ould be colder (pictets

  12. I am not disputing that the temperature of a cold environment of a body influences that rate of cooling of the body with transfer of heat energy from warm body to cold environment, only that there is never any heat transfer from cold to warm. Never, according to the 2nd law.

  13. I am not sure if you are understanding what I am saying to you here?

    The Earth is a heated body just like Pictets Thermometer was a heated body. If you alter the temperature of pictets cool body you can raise or lower the temperature of the hotter body at will. If you alter the cooler temperature of the Earths atmosphere you can raise or lower the temperature of the Earths surface at will.

  14. I understand what you are saying and I can only repeat that un-forced transfer of heat energy from cold to warm would violate the 2nd law, and I get the impression that you are not understanding what I am saying.

  15. Ok well i need a bit of help understanding what you are saying. You are saying the idea of 3. supports CO2 warming hysteria. and apparently using pictets experiment to support 1.
    Pictets experiments supports the idea of global warming. because a warmer colder object causes a heated object to become warmer and there is totally no need to give me an answer that involves the second law.

    Is there something i am missing here??

  16. If you cannot understand that transfer of heat from cold to warm without forcing violates the 2nd law, then I cannot help you. Advocacy that this is anyway possible because there is more transfer from warm to very cold than from warm to moderately cold, is simply missing the point, and if you do not understand that then there is no meaning continuing the discussion.

  17. That is a very unfair answer. You are claiming the global warming idea violates the second law. I am pointing out to that it does not. The heat flow is from the surface to the atmosphere to outerspace. Obviously the atmosphere is not heating the surface. The surface is simply warmer because we are not exposed to the terrifying consequences of being cooled by a 3k environment which would rapidly cool this planet. There is no 3k environment and therefore we have less cooling and therefore while heated we are warmer.

  18. Claes, if you are correct here then please have a go at explaining how my explanation of the global warming idea is violating the second law when I believe we are warmer because we are not exposed to the terrifying consequences of having a line of sight to a 3k environment and my explanation apparently has no violations at all.

  19. If this is what you are saying, then it is an obvious fact but as such not interesting. The question is how much warmer and why, and that is what I find of interest to understand.

  20. Thanks for clearing that up. Out of interest does your wave? theory predict anything different to the current theory? I would have imagined by now that very precise quantifications of heating by radiation had been carried so that stefan boltzmann calculations had not been falsified. I seem to recall after the law was published work was done to prove it. Of course we can say that means nothing. How can your idea be tested to be different to the current mainstream idea?

  21. What is the current mainstream idea: two-way flow of photon particles transferring heat energy back and forth between two bodies?

  22. By definition these days it appears we are not allowed to say heat is going back and forth between bodies. Heat is a quantity being transferred in only one direction.

    In the old days (I suppose when we younger) they talked about heat rays but all EMR can be seen as heat rays.

    So by definition these days when you talk about IR you cannot say "two-way flow of photon particles transferring heat energy back and forth between two bodies?" You have to leave out the word heat. In the modern mainstream idea only energy goes back and forth.

  23. If you are not speaking about energy measured in degrees Kelvin or Celsius, then I do not understand what you are talking about and the discussion seems meaningless.

  24. You can have tremendously hot objects with relatively very little energy. So we do not measure energy in degrees of temperature. Energy can do work so it is measured in joules and watts and so forth.
    I am supposing you must know that and presumably i am missing something again. Anyway since hot things heat cold things there is only one flow of heat even if there is a two way flow of energy. in the old days heat existed in an object but these days people are talking about heat as a quantity that is in transit as a flow of heat. Heat always flows from hot to cold - same as it did in the old days! :-)

  25. Claes, reading thru your blog i have got very confused as to whether you are still disputing the global warming idea or you are only saying there is no evidence for backradiation. For example some people say the cosmic microwave radiation heats earth, which is is conceptually wrong. What is correct is that the cosmic background slows down the cooling rate of the Earth which is a heated object and therefore we are warmer. Stefan came up with his law using the cooling data of several famous french scientists and obviously that data is only valid if you have a cooling hot object in the presence of a colder environment because the cooling rate changes depending on the temperature of the environment. I see you have focused mainly (only) on Planck? I note also there are a number of experiments on Utube where people are demonstrating a very simple electrical method of deriving the stefan boltzmann constant using a light bulb. So in the beginning came simple experimental data and then people sought to explain it, where long before quantum mechanics came along people were aware there was a simple relationship of a hot object in a given warm environment that involved a constant and a fourth power of the absolute temperature.
    Where are we actually at this point in time in this discussion?

  26. I know where I am but I that may not be helpful to you. I have expressed myself in extenso and I don't see there is much point repeating my point of view another time.
    And yes, I am disputing the idea of measurable impact on global temperature by human emisssion of CO2 and what is not measurable cannot be of any big importance. The reason I am disputing this claim by IPCC and global warming alarmists, is that there us no scientific evidence of such an effect, only fantasy and here backradiation as fantasy serves a major role to support the fantasy of AGW.

  27. Are you however saying water has no role in creating a warmer earth? Are you saying it is also impossible to calculate/estimate what possible impact water can have? As I tried to point out before backradiation does not really change the simple experimental evidence that warmer cold things cause hot things heating those warmer cold things to become warmer. What actually is your scientific basis for saying CO2 cannot possibly cause a warmer earth?