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I have put into the lead the modifying phrase 'especially in', to say "especially in thermodynamics". The definition of heat used here is the carefully developed fruit of experiments interpreted in terms of thermodynamics. The modifying phrase makes it clearer and more explicit in the lead of the article that the definition of heat here used is a special definition. This should help to allay concerns that have been expressed on this talk page, that may perhaps to some degree be reasonable, that the present definition has in some sense arrogated the word heat without proper justification or notice. Chjoaygame ( talk) 09:06, 2 April 2012 (UTC)
The term "thermal energy" is not a standard term strictly defined by standard texts that I am familiar with. I think some homework needs to be done on this term so that this term should be well sourced from reliable sources, or that it should be made explicitly clear in the article that it is not to be found in reliable sources, or that the term should be removed from the article. Chjoaygame ( talk) 03:48, 24 March 2012 (UTC)
Again, if you're going to challenge the above-quoted WP:IRS policy in some way, you need to go to WT:IRS (the IRS talk page) and make your case there, not here. Go and complain that somebody is trying to use the "minimal standards" and you'd like it deleted. However, since I quoted to you from a Google Scholar paper, we've provided you with both primary scientific paper uses of "thermal energy" as well as two textbook uses of the term of art in engineering (as noted in the lede) so it's not at all clear what you're going to complain of, there. Texts are said in WP:IRS to be preferred over research papers, even though papers (as the one I quoted from an academic press) have been peer-reviewed, and sometimes textbooks are not.
Again, you should not think from this that I agree with WP's "rules" in this, as they can result in bad articles on WP (I ran into that problem in fighting bad physics textbook definitions of weight-- which is an article that still includes stupid definitions that allow weightless astronauts in orbit to have 90% of ground weight, as GR's cancelling effect on the major component of g in certain inertial frames is ignored, since some beginning college texts ignore it). The secondary sources (as in this case) may be sloppily-written textbooks for freshmen written by authors who aren't Ph.D. scientists (or else are not writing in their own field of expertise) and they disagree with each other, or make mistakes. So it's not always true that the preferred secondary sources are always better than primary sources. Sometimes primary sources are all that exist. In other cases, texts have worse standards. Again, however, here is not the place to argue that. I've been there, done that. If you want to take up this banner, you go, girl. I'll stand aside and cheer for you. S B H arris 17:49, 6 April 2012 (UTC)
I accept that the wording that I wrote is very terse. The undone edit adds many words, which I do not see as improving the terser wording. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
First paragraph:
I find this edit introduces uninformative verbiage, and to be inaccurate. Heat processes do not have to cause change in temperature; transfer of heat is driven by difference in temperature, not the other way round. Telling us here that temperature changes are associated with other changes is simply chatty. Telling us that thermodynamics is an aspect of physics is uninformative; it is enough to say that it is in physics. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
Second paragraph:
Again I find this introduces unnecessary verbiage. Heat does not refer to nearly macroscopic behaviour, whatever that might be. The microscopic motions themselves are explanatory, and do not need to be wrapped up as 'modes'. The explanations are good, not merely adequate. 'Bodies' is near enough, and traditional, and does not need to be, indeed is better not, expanded into 'objects or media'. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
Next paragraph:
Again I find this introduces unnecessary verbiage. There is real diversity of meaning, not merely variation. The word 'conversely' has a technical meaning which is irrelevant here and is here not actually meant. Really we do not need to know that practitioners are are talking to parties. I think it is distracting to read that the research has taken three and a half centuries. It is getting to be simply chatty. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
Again, I accept that the wording that I wrote is very terse. It is so for carefully thought out reasons. The new revisions are mainly in a summary and an overview, not in a detailed section of the article. Some grammatical filler words that might at first sight seem called for would potentially mislead if they were put in, and are better left out. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame ( talk) 14:45, 15 April 2012 (UTC)
I well understand Count Iblis' reason for his reversion to the old version, and I accept that a case can be argued for it. Indeed it is true that there exists a rigorous definition of a quantity of energy transferred other than by work, that does not refer to temperature, but that does not make it a definition of heat; it does not relate to heat until it relates to temperature. Carathéodory's 1909 paper, relied upon by Born 1921, and the source of the divergence of definitions, does not actually define heat in its own terms, although it defines temperature. Carathéodory's statement of the first law of thermodynamics does not admit the notion of heat. It is customary, though perhaps mistaken, to say that the zeroth law of thermodynamics helps in the definition of temperature. This suggests that the idea of temperature is considered preliminary to the statement of the first law of thermodynamics. This weakens the case that temperature is really not involved in the first law of thermodynamics. Close examination of Carathéodory's statements about his first axiom leave it in doubt whether he has really made a statement about a conservation law, or merely, as is explicit in his own words, made a statement of the existence of a function of state that he chooses arbitrarily to consider and call "internal energy".
Because of the diversity of meanings and points of view in physics for the word heat, it is inappropriate to insist on just one very exclusive definition in the lead; detailed definition should in this case be considered in sections of the body of the article. The definitions of heat that explicitly refer to temperature are also rigorously valid, as considered for example by Maxwell, Planck, and Kirkwood & Oppenheim. It is a matter of taste to prefer the very exclusive definition that Count Iblis and certain other editors consider best, but there are several other editors whose tastes do not concur with it. The new version of the article admits the Bryan-Carathéodory-Born definition of heat, but does not try to deal with the detail of the diversity of definitions in the lead.
The new lead does not pretend to define heat in detail, but defers detailed definition to the body of the article, and instead makes a true statement about heat that is more or less expected by several editors. Heat is indeed related to temperature, if not by definition then by deduction. It is a valid point of view that it must be defined without reference to temperature, but not the only valid point of view.
I think that insistence on the exclusively rigorous definition of heat, that does not mention temperature, being stated in the lead is an arbitrary exercise of personal taste, and tends to push a particular point of view to the exclusion of others.
Therefore I have undone the reversion by Count Iblis. Chjoaygame ( talk) 16:35, 15 April 2012 (UTC) Chjoaygame ( talk) 16:44, 15 April 2012 (UTC)
Discuss... Count Iblis ( talk) 00:17, 16 April 2012 (UTC)
Which will obviously add heat to the system. Note that we're free to define what e exactly mean by "system". So, if the reply is going to be along the lines that I can't choose to define the system with its system boundaries and external parameters in the way I like, then there is a problem with the theory you are defending.
While I am performing work, there is no (negative) thermodynamic work performed by the system, because its external parameters don't change from start to beginning. The initial state was in some well defined thermodynamic state, so is the final state. The temperature of the system has increased, so heat was added to the system, but it didn't flow to it from some hotter object. Count Iblis ( talk) 00:37, 16 April 2012 (UTC)
I'm trying to understand your other point. It requires TIME for vibrational energy input (like friction or certain types of uneven heating) to completely thermalize in a system, so that the entropy of this added energy is finally maximized. Thermodynamics isn't very good about describing systems in such flux (unless the thermal energy spreads with minimal temp differences from region to region), because the system has expanded in phase space, but not (even at any "point") to the maximum (equilibrium = highest entropy). So yes, thermo doesn't have much to say about it. Nor does physics has much to say about it, because it's a lot of particles in states that we can't know, and it's just too damn complicated for any theory there is. But I sort of take that as a given. We use thermo for situations where thermo was designed to give answers, and that's in slow processes where equilibrium has been reached in most or all "places." And by "places" I mean in collections of atoms large enough to give a statistical temperature and thus have a heat capacity, as happens even while heat is being conducted through a solid. In engineering, for example, even in problems of conductive heat flow, we pretend that the temperature field T(x,y,z) is composed of points. Of course it is not. It is composed of little bits of matter each of which has enough atoms that allow it to have a well-defined statistical temperature, which means that locally it has reached equilibrium and maximal entropy for the energy it contains. But nature is so fine-grained that in most systems this works like mechanics, with large objects, works without resorting to quantum mechanics.
In QM, as I've noted, thermo gets very much harder and Bolzmann-Gibbs entropy goes over to von Neumann entropy and you do have to worry about wave-function collapse. But that's a separate problem from the problems of large-scale non-equilibrium systems (your shaking bottle, or systems with frictive imputs), these are more like the problems of predicting the weather. There's just too much chaos and information, and we simply need to acknowledge that there is no theory that works. S B H arris 18:08, 16 April 2012 (UTC)
Yes, in a free expansion experiment, you could look at the work done by the gas, and say tha tthis is zero. However, then you ahve chopped up thesystme in subssystems and are looking at the work done by the subsystems on each other. Now, as Reif explains in his book, thermodynamics is misnomer, it should have been called thermostatics, as it only describes systems in thermal equilibrium. But that doesn't mean that it cannot be applied to systems that undergo rapid change. You can derive exact statements using thermodynamics for such processes, like in case of the free expansion experiment.
Of course, such results involve initial and final states that are in thermal equilibrium. But that is a powerful reason not to make the definition of heat and work dependent on the details as SBHarris argues above, because that would make obscure the fact that such a results are rigorous (i.e. it is not conditional on being able to define temperature while the system is indergoing change, which is not possible to do precisely).
Another comment. It is temperature that is defined using the potential of heat flow when different systems are brought into thermal contact. One doesn't define heat in this way. And how would you define temperature if you were to chose this definition of heat (let's forget for the moment that this defintion of heat is problematic)? One can try the high school definition of temperature in terms of kinetic energy of particles, but this is problematic. That definition assumes the equipartition theorem, which isn't valid in quantum mechancs.
Even for classical systems, it won't work, because it would fail to capture a very fundamental aspects of thermodynamics, i.e. that it ultimately derives from an information theoretic description of a system. It is lack of information about the system that makes a thermodynbamic description useful. Entropy is proportional to the number of bits of intormation that you would need to fully describe the exact state of a system, give the macroscopc thermodynamic specification. Now, if you know all the velocities of all the particles, you have a complete description of the system, the entropy is then identically zero. Temperature remains equal to absolute zero at all times, no matter "how hot" the system gets, as suggested by the velocity distribution of the particles.
If you have complete information about a system, you can let Maxwell's demon be effective, it doesn't have to dump its memory (the Landauer bound is thus irrelevant here). The demon knows in advance when the next molecule will come along for which it has to open the gate, by looking up the system specification and doing some computations. This variant of Maxwell's demon is called "Laplace's demon". Clearly this makes any attempt to base thermodynamics on anything other than information theory paradoxical, as what you would get would be vulneralble to such thought experiments involving demons.
What i.m.o. is the big lesson here is that heat, temperature, entropy etc. etc. are to some extent subjective quantitites, that ultimately derive from how we choose to describe a system. In practice, when deriving thermodynamics from statistical physics in the usual way, you encounter this "subjectivity" when defining the Omega function Omega(E), which govesthe number of energy eigenstates between E and E + Delta E. You could say that we should take the limit of Delta E to zero and work with the density of states. However, Omega(E) should be the number of states the system can be in, and Delta E is a finite quantity. If Delta E were zero, you would know which state the system is in, so you would have complete information about the system's microstate. Now when we look at the familiar thermodynamic quantities, like entropy S = k Log(Omega), then it turns out that the Delta E dependence is utterly negligible, and that dependence vanishes completely when taking the thermodynamic limit. Count Iblis ( talk) 02:17, 20 April 2012 (UTC)
It should be plain to any reader that instead of getting better the article is getting worse. For example, there is a "lede too long" tag. While the complaint is technically correct, length is not the operative problem. The underlying reason, which is not confined to the lede, is that both the writing and rationale are incoherent, ill-organised, doubtfully expressed, opaque to the reader unversed in physics, assailable to physicists, and self-indulgent. It certainly is neither encyclopedic in its current form, nor very Wikipedic. No names, no pack drill. At the current rate we will get no further than snapping at each other. This is as nauseating an example as ever I have seen, of trying to see further than others by standing on their toes rather than on their shoulders.
Now, the problem is not that there is a deficiency of available expertise in the subject matter. Nor is it clear that we could rescue the project by having any one person rewrite the whole thing (we certainly could, but how are we to identify the right person?) We definitely cannot do anything constructive in the current dogfight mode. Conversely, we cannot afford to let the existing mess stand as a WP article.
So?
So I am not going to prescribe or even propose what the article should look like, thereby prolonging the exchange of spittle and ink, but I do propose that anyone who wants to go off into a fit of the vapours do so now and let the rest get some work done. He can come back later and sneer if he chooses. Those remaining, I suggest that they leave the article alone for a while, archive most of this talk page, and each go off and work out not proposed text or material content, but a section layout. Then compare their products on the talk page. Given goodwill and flexibility that should not be so hard. The major principle should be that one does not veto material that is neither wrong nor better suited to a different or separate article; instead just put discrepant discussions into separate sections.
Then start rewriting each section till either there is a complete article, or it appears that there is a need to split, add or rearrange sections. Steer clear of editing each other's sections, short of actual error corrections. If one person turns to be writing in engineering terms and another in statistical terms, then put those two topics in separate sections for now. Worry about splitting the article later if at all.
And so on.
When all is done (if ever) either split the product into the right number of articles (if desirable) or call in a reader who is not a physicist but is literate and competent in lay English, and engage him or her to work on it till s/he and friends find it reasonably concise, easy to read and possibly to comprehend, without making physicists' teeth curl. No more of this argumentation about terseness and chattiness. Let's have a bit more competence and a lot less possessiveness. This is not a matter of taste, but of function, and infelicities are not just matters of literary taste, but sources of distraction and confusion. Opinions do matter, but not as a substitute for linguistic skills or hard fact.
And if anyone goes into sabotage mode, the rest of us can go into arbitration mode, and see who is left standing. This damned slanging match should stop. Round about now.
Now, no-one need take this exhortation too seriously, and I know some of us will hate it with all the fury of possessive parents, but when they have finished flinging their plates of porridge from their high chairs, I ask all and any of you: is it any worse than the mess currently in this talk page, or the proud product you see before you in the article? JonRichfield ( talk) 09:30, 18 April 2012 (UTC)
Much of the rest of our definitional problems is a holdout from the days of now-banned user user:Sadi Carnot, who insisted on the purity of usage that heat had to be thermal energy in the act of transfer (thus, heat = heat transfer always), and the very word "heat" even in science, could never apply to thermal energy residing in materials, not moving along a temperature gradient. But there's a residual of usage of heat to mean static thermal energy going back in science a long away, and some of it still remains (as in calling enthalpy "heat content"). Finally, there's a band of people who insist that the purely thermal component of the internal energy of an object or system (which is NOT enthalpy, since it doesn't include mechanical work input or output) can't EVEN be defined, and shouldn't be talked about, even though engineers use the idea all the time (as a differential and change, at least), and use it in their heat capacity calculations in heat transfer. I don't know what to do about these people. When doing calculations, it works. It does not give wrong answers. My opinion is that if it works, it's valid. S B H arris 16:42, 18 April 2012 (UTC)
The heat of a substance or body is the property that gives the sensation of hotness or warmth. Heat is measured by temperature, indicated by a thermometer. A number of different scales have been devised so that thermometers can indicate temperature in a convenient way, usually by the inventors of thermometers. Currently the most used scales are Celsius and Fahrenheit but many have been used down the ages; for some scientific work the Kelvin or Rankine scales is used; these scales have as zero the lowest possible temperature, known as absolute zero; the Kelvin scale has the same size of divisions as the Celsius scale but they are called Kelvins (K); the Rankine scale has the same size of divisions as the Fahrenheit scale the divisions are called 'degrees Rankine' (°Ra).
I suggest that small revisions be highlighted in colour; I tried to put the text in red but failed to find out how to 'do' colour.-- Damorbel ( talk) 08:15, 19 April 2012 (UTC)
Heat and temperature have different physical units, and cannot be connected without using the concept of entropy. Temperature is proportional to the mean kinetic energy of an ensemble of particles in thermal equilibrium; heat is only connected to kinetic energy insofar as it sets the temperatures which cause the energy of heat to flow. The particular type of energy that composes heat is drawn partly from the kinetic energy of particles in matter in thermal equilibrium, but in all real situation such thermal energy is composed of other types of energy as well, which are distributed according to a partition function that varies from substance to substance. S B H arris 17:55, 19 April 2012 (UTC)
we solve such problems with other words that have both common and tech meanings, by having the word direct to the dab page, and have the technical meaning with a paren. Thus, work directs to the work (disambiguation) and if you want the type of work that comes in in joules, you need to go to the technical work (physics) or work (thermodynamics). But heat directs here, since there isn't a heat (physics). Instead, people have insisted on shoehorning popular usages into this article, which otherwise could be a technical one. It's stupid, but there it is.
I've suggested otherwise before, but gotten little support. See above. Want to try this again as a suggestion? That would mean this article would be renamed heat (physics) or heat (thermodynamics). Actually, I think there's enough difference in the really technical thermo term to have a heat (thermodynamics) article where we only discuss heat transfer, and perhaps ALSO a heat (physics) article we could discuss arcane ideas like heat content and what we call the energy that results in heat capacity, when it's not going anywhere (i.e., the isovolemic or non-work component of internal energy change). What engineers often think of as heat (more than just heat transfer, but still measured in joules). That would at least cut down on the lede length, in the science articles. S B H arris 21:06, 19 April 2012 (UTC)
There is a perfectly usable definition of the part of internal energy that is thermal, and that is-- it's the part that has been thermalized, so that it cannot then be withdrawn EXCEPT as heat! That happens immediately to energy you add as heat flow, but it takes time with other types. A very slow compression work is immediately thermalized and immediately irreversible (if you want the energy back, you pay max entropy cost for it). A fast compression generates shock waves that bounce back and forth and take time to thermalize, and during that time, you can get some of your original work back because entropy hasn't increased to the max for the energy you added. Thermal energy is energy that has maximized its entropy for its temperature, by finding all degrees of freedom in the system available to it. That takes time, and I suppose it should thus be noted that the amount of thermal energy that resides in an object, is thus a function of time. But it's a useful concept if you know your timescale.
One of my favorite examples is in the proton spins of ortho vs para hydrogen. At room temp there's enough energy that 75% of H2 is ortho (spin aligned) which is a high energy state, see spin isomers of hydrogen. When you liquidfy the stuff, this should equilibrate to the low energy form, but it takes days to do so-- at first you liquid hydrogen has the same ratios of ortho/para as it did at room temp! The heat the ortho--> para conversion generates is enough to boil the liquid again, so engineers have to use a catalyst to get the extra energy out (thermalize it). Essentially, when you liquify H2 from room temp, the various translational and vibrational modes all go to 20 K, but the spin-temperature stays at room temp for awhile, as though this thermal energy were in an insulated compartment at a higher temp! There's a lovely example of having a kinetic barrier to thermal equilibrium and removal of maximal thermal energy. But it does eventually happen. You can think of it as a sort of slow phase change, and the spin-isomeric transition as a sort of latent heat. But that's not a perfect analogy, since in other phase changes the temperature of the phases is the same. Here, the spin-temp of the H2 is higher than the temp of the liquid, but heat cannot flow by conduction or diffusion. It has to flow in tricky ways to get energy from nuclei into energy of translation of molecules. It is a form of stored "heat" however, as it acts like thermalized energy at room temp, and you can't convert it to work, willy-nilly. The spin isomer energy has equilibrated with thermal energy at room temp, and it acts like themal energy at room temp, even after you've cooled the hydrogen down to cryogenic temps. S B H arris 23:19, 20 April 2012 (UTC)
There have been some recent edits for the term "thermal energy". Chjoaygame ( talk) 03:16, 6 April 2012 (UTC)
On this talk page, one editor put the view that the words 'thermal' and 'energy' could be put together to form the phrase 'thermal energy' as a simple matter of ordinary syntax. This view would make perfect sense to someone who believed in the caloric theory of heat. The caloric theory of heat is not valid in thermodynamics, but it is not a silly theory in that under special conditions when energy cannot be transferred as work or chemical potential energy, but only as heat, as considered by no less a physicist-chemist combination than Laplace and Lavoisier, then quantity of heat transferred obeys the law of conservation of energy. The difficulty for the caloric theory arises when modes of energy transfer other than thermal are allowed. Such revered figures as Carnot and Kelvin were not clear in their minds about this in the early days, until the first law of thermodynamics was well understood. In general such other modes are allowed in thermodynamics; moreover there is no general resolution of internal energy into thermal and non-thermal components; that is part of the import of the first law of thermodynamics.
In tags to proposed edits, another editor puts the view that Wikipedia should effectively ratify the use of the term "thermal energy" because it is sometimes used by engineers. In the lead that he proposes, he argues that the term "thermal energy" is naturally related to heat capacity. In the lead that he proposes, he offers what, at first glance by a non-thermodynamicist, looks like a precise definition of amount of "thermal energy", and offers what looks like a definition of temperature as "the mean kinetic energy [...] of the system". These definitions again would make perfect sense to someone who believed in the caloric theory of heat,and they seem to conform with ordinary language usage. This proposed lead cites page 14 of an engineering text by Incropera and others. The library is closed today and for the moment I must make do with pages from another version of that text from the internet. On page 2 the authors write of "thermal energy in transit". The authors often are careful to write of "the sum of thermal and mechanical energy", and they write of "thermal energy generation". On page 9 they write: "Radiation that is emitted by the surface originates from the thermal energy of matter ...". On page 10 they write: "A portion, or all, of the irradiation may be absorbed by the surface, thereby increasing the thermal energy of the material". They repeatedly use the term "thermal energy" like this on page 10. It seems to me that these are occasions of lapse from sound expression or thinking by these authors, not consistent with their care on other occasions. (Also it is relevant that heat can pass through a surface, which has two dimensions, but can be absorbed only by a body with three dimensions.) On page 16 they write: "the sensible and latent components of the internal energy (Usens and Ulat respectively), which are together referred to as thermal energy." This looks like an explicit definition of "thermal energy" as a component amount of heat in a body. But it also looks like a lapse into the caloric theory way of thinking, because more properly in thermodynamics, sensible and latent heats are defined not as components of internal energy but as components of heat transferred. It is clear enough that we are looking here at special engineering usage, that is not supported by the ordinary line of thinking in thermodynamics.
Perhaps a solution to this would be to put into the article an explicit statement that engineering usage sometimes departs from ordinary thermodynamic usage in ways that could be specified. I would suggest that the lead should only advert to the matter, not detail it or argue for it as is done in the currently proposed version. I would suggest that detail and argument be kept to the body of the article. Chjoaygame ( talk) 03:16, 6 April 2012 (UTC)
The lede now does differentiate thermodynamic use from engineering use. Engineering use doesn't "differ" from thermodynamics (which simply says nothing on the subject in the modern formulation), but rather extends it (breaking internal energy down into components of interest). Thermodynamics is not concerned with many heat transfer situations, such as heat conduction/transfer within solids. So it lacks terminology for what happens there. Engineers and physicists are forced to treat conduction and convection, however, and they need terms of art to do it. In all heat transfer problems, energy conservation IS thermal energy conservation (you can call that "caloric theory" if you like, but it is still true), so the components of internal energy that are thermal and nonthermal need to be identified (or else you cannot predict temperature-field evolution within your system). That is what is happening here, in terminology. "Thermal energy" is a very useful, even essential, term of art in treating thermal conduction and convection.
As to whether thermal energy is "latent heat plus sensible heat" or "sensible heat" alone, it appears from what you've written that Incropora and DeWitt may have changed their minds on this between editions. There may even be disagreements between texts on whether or not latent heat is to be incorporated into thermal energy. If a system has ways of storing or giving up sensible heat, clearly this needs to be taken into account when you do heat conduction problems (for example a microwaved caserole that is full of little bits of ice). If there are no phase changes involved, so that any internal energy changes result in termperature changes, then the sensible heat concept is enough. The point is that engineers need a term for ALL of the part of internal energy that is available if you want to extract heat from the system or object, using a cold reservoir, and this certainly includes both latent and sensible heat. This is called "thermal energy." If thermodynamics has a name for it, please let me know. Clearly a term is needed, and engineers have one. Thermal energy is that term. S B H arris 18:35, 6 April 2012 (UTC)
Chjoaygame, you write:- "These definitions again would make perfect sense to someone who believed in the caloric theory of heat". The term 'thermal energy' was applied by J C Maxwell to the kinetic theory as he developed it, it has nothing in common with the caloric theory. Kinetic theory was developed by Maxwell and others because Lavoisier's caloric theory where heat was considered to be a fluid, simply did not explain many observations such as 'heat is not conserved' and the particle (atomic) nature of matter; there is no possible way to explain quantum effects by caloric theory. -- Damorbel ( talk) 06:07, 6 April 2012 (UTC)
The term "thermal energy" appears in many thousands of books; no doubt many of those uses would be wrong, or unsatisfying, to a thermodynamicist. Yet others are probably used in a more rigorously correct way, where the inability to in general distinguish thermal from other types of energy is recognized, or at least not violated. So the issue is not whether to use "thermal energy", but where and when to use it without being incorrect, or without being significantly incorrect in practice. Dicklyon ( talk) 07:02, 6 April 2012 (UTC)
Dickylon, I know of no places where there is any difficulty figuring out which part of thermodynamic "internal energy" is "thermal energy." Thermal energy by all definitions is the part of internal energy that changes when you add heat to an object, or extract heat from it. It is also the part of internal energy that you can, in theory and practice, extract as heat, using a cold reservoir. That is simple enough, but absolutely essential if you're looking at problems of heat conduction (with heat sources and sinks added), which thermodynamics largely ignores. Conservation of internal energy is not enough to do all heat transfer problems, particularly transient conduction problems: for that, conservation of energy needs to be translated into temperature changes in some way (see heat equation), and in order to do that, you need the concept of heat capacity, or thermal diffusivity of which heat capacity is an essential component. Integration of heat capacity and temperature (plus phase change energy if you have any of that happening) gives an energy term which defines thermal energy, and yet is not internal energy (rather is the part of internal energy that is available to make or absorb heat, even if the heat hasn't been extracted from the object or system, yet). In many problems, if there were no term for this, you'd have to define it mathematically and make up a term. Well, engineers have made up a term! Thermal energy is what thermodynamicists used to call "heat content" (I don't know if they still do or not). But whether or not they do, what is the problem, here? Engineers need a term. So would thermodynamicists if they did engineering heat transfer problems. S B H arris 18:18, 6 April 2012 (UTC)
In response to Comment 2 made by Dicklyon, I would say that it is an issue as to whether we make the Wikipedia appear to ratify the term "thermal energy" as a properly defined technical term or term of art; or whether we leave it as a phrase that can occur in the ordinary language as opposed to as a term of art, which the Wikipedia has no automatic duty to examine. Chjoaygame ( talk) 08:22, 6 April 2012 (UTC)
You can fulminate all you like about what you think WP SHOULD be, but often such opinions fail in the face of seeing what WP actually IS. All that means is you don't have enough experience here. So stick around. You can give your opinions, but as a newb (experience-wise-- just making edits for three years in and of itself doesn't count), we don't really have to take you seriously until you know what you're talking about. It takes 10,000 hours to master any complex subject, and probably that long to really know WP. I'm not even there, yet, and I've 15 times your edits, on a vastly great range of topics, and a lot of arguing on WT. Your 2000 edits, almost entirely on things like Planck's law and thermo topics, and almost nothing in the WP: or WT: namespaces, does not qualify you as to any expertise as to how Wikipedia works. Please try to know what you don't know. If I need to know more about Planck's law, I'll come to you (years ago you might have explained to me why lambda(max) and frequency(max) of the blackbody curve don't multiply to c; but I understand that now). However, when it comes to how WP works and what it is, perhaps you could slap that student sign on your forehead. As we all need to frequently with most areas of our lives.
In any case, thermal energy is clearly a term of art in heat transfer engineering (hell, do you know anyone who uses this in common language?!), and so should be discussed and have an article on WP. If the engineers sometime cannot agree whether to include latent heat in it, that makes it no worse than many another term in science, not all of which are defined by the CIPM or NIST (see weight, where nobody seems to care about ISO). Some terms like matter have even worse definitional problems. This article on heat is nothing special in that regard. S B H arris 18:40, 7 April 2012 (UTC)
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was invoked but never defined (see the
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I have put into the lead the modifying phrase 'especially in', to say "especially in thermodynamics". The definition of heat used here is the carefully developed fruit of experiments interpreted in terms of thermodynamics. The modifying phrase makes it clearer and more explicit in the lead of the article that the definition of heat here used is a special definition. This should help to allay concerns that have been expressed on this talk page, that may perhaps to some degree be reasonable, that the present definition has in some sense arrogated the word heat without proper justification or notice. Chjoaygame ( talk) 09:06, 2 April 2012 (UTC)
The term "thermal energy" is not a standard term strictly defined by standard texts that I am familiar with. I think some homework needs to be done on this term so that this term should be well sourced from reliable sources, or that it should be made explicitly clear in the article that it is not to be found in reliable sources, or that the term should be removed from the article. Chjoaygame ( talk) 03:48, 24 March 2012 (UTC)
Again, if you're going to challenge the above-quoted WP:IRS policy in some way, you need to go to WT:IRS (the IRS talk page) and make your case there, not here. Go and complain that somebody is trying to use the "minimal standards" and you'd like it deleted. However, since I quoted to you from a Google Scholar paper, we've provided you with both primary scientific paper uses of "thermal energy" as well as two textbook uses of the term of art in engineering (as noted in the lede) so it's not at all clear what you're going to complain of, there. Texts are said in WP:IRS to be preferred over research papers, even though papers (as the one I quoted from an academic press) have been peer-reviewed, and sometimes textbooks are not.
Again, you should not think from this that I agree with WP's "rules" in this, as they can result in bad articles on WP (I ran into that problem in fighting bad physics textbook definitions of weight-- which is an article that still includes stupid definitions that allow weightless astronauts in orbit to have 90% of ground weight, as GR's cancelling effect on the major component of g in certain inertial frames is ignored, since some beginning college texts ignore it). The secondary sources (as in this case) may be sloppily-written textbooks for freshmen written by authors who aren't Ph.D. scientists (or else are not writing in their own field of expertise) and they disagree with each other, or make mistakes. So it's not always true that the preferred secondary sources are always better than primary sources. Sometimes primary sources are all that exist. In other cases, texts have worse standards. Again, however, here is not the place to argue that. I've been there, done that. If you want to take up this banner, you go, girl. I'll stand aside and cheer for you. S B H arris 17:49, 6 April 2012 (UTC)
I accept that the wording that I wrote is very terse. The undone edit adds many words, which I do not see as improving the terser wording. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
First paragraph:
I find this edit introduces uninformative verbiage, and to be inaccurate. Heat processes do not have to cause change in temperature; transfer of heat is driven by difference in temperature, not the other way round. Telling us here that temperature changes are associated with other changes is simply chatty. Telling us that thermodynamics is an aspect of physics is uninformative; it is enough to say that it is in physics. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
Second paragraph:
Again I find this introduces unnecessary verbiage. Heat does not refer to nearly macroscopic behaviour, whatever that might be. The microscopic motions themselves are explanatory, and do not need to be wrapped up as 'modes'. The explanations are good, not merely adequate. 'Bodies' is near enough, and traditional, and does not need to be, indeed is better not, expanded into 'objects or media'. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
Next paragraph:
Again I find this introduces unnecessary verbiage. There is real diversity of meaning, not merely variation. The word 'conversely' has a technical meaning which is irrelevant here and is here not actually meant. Really we do not need to know that practitioners are are talking to parties. I think it is distracting to read that the research has taken three and a half centuries. It is getting to be simply chatty. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame
Again, I accept that the wording that I wrote is very terse. It is so for carefully thought out reasons. The new revisions are mainly in a summary and an overview, not in a detailed section of the article. Some grammatical filler words that might at first sight seem called for would potentially mislead if they were put in, and are better left out. Chjoaygame ( talk) 13:45, 15 April 2012 (UTC) Chjoaygame ( talk) 14:45, 15 April 2012 (UTC)
I well understand Count Iblis' reason for his reversion to the old version, and I accept that a case can be argued for it. Indeed it is true that there exists a rigorous definition of a quantity of energy transferred other than by work, that does not refer to temperature, but that does not make it a definition of heat; it does not relate to heat until it relates to temperature. Carathéodory's 1909 paper, relied upon by Born 1921, and the source of the divergence of definitions, does not actually define heat in its own terms, although it defines temperature. Carathéodory's statement of the first law of thermodynamics does not admit the notion of heat. It is customary, though perhaps mistaken, to say that the zeroth law of thermodynamics helps in the definition of temperature. This suggests that the idea of temperature is considered preliminary to the statement of the first law of thermodynamics. This weakens the case that temperature is really not involved in the first law of thermodynamics. Close examination of Carathéodory's statements about his first axiom leave it in doubt whether he has really made a statement about a conservation law, or merely, as is explicit in his own words, made a statement of the existence of a function of state that he chooses arbitrarily to consider and call "internal energy".
Because of the diversity of meanings and points of view in physics for the word heat, it is inappropriate to insist on just one very exclusive definition in the lead; detailed definition should in this case be considered in sections of the body of the article. The definitions of heat that explicitly refer to temperature are also rigorously valid, as considered for example by Maxwell, Planck, and Kirkwood & Oppenheim. It is a matter of taste to prefer the very exclusive definition that Count Iblis and certain other editors consider best, but there are several other editors whose tastes do not concur with it. The new version of the article admits the Bryan-Carathéodory-Born definition of heat, but does not try to deal with the detail of the diversity of definitions in the lead.
The new lead does not pretend to define heat in detail, but defers detailed definition to the body of the article, and instead makes a true statement about heat that is more or less expected by several editors. Heat is indeed related to temperature, if not by definition then by deduction. It is a valid point of view that it must be defined without reference to temperature, but not the only valid point of view.
I think that insistence on the exclusively rigorous definition of heat, that does not mention temperature, being stated in the lead is an arbitrary exercise of personal taste, and tends to push a particular point of view to the exclusion of others.
Therefore I have undone the reversion by Count Iblis. Chjoaygame ( talk) 16:35, 15 April 2012 (UTC) Chjoaygame ( talk) 16:44, 15 April 2012 (UTC)
Discuss... Count Iblis ( talk) 00:17, 16 April 2012 (UTC)
Which will obviously add heat to the system. Note that we're free to define what e exactly mean by "system". So, if the reply is going to be along the lines that I can't choose to define the system with its system boundaries and external parameters in the way I like, then there is a problem with the theory you are defending.
While I am performing work, there is no (negative) thermodynamic work performed by the system, because its external parameters don't change from start to beginning. The initial state was in some well defined thermodynamic state, so is the final state. The temperature of the system has increased, so heat was added to the system, but it didn't flow to it from some hotter object. Count Iblis ( talk) 00:37, 16 April 2012 (UTC)
I'm trying to understand your other point. It requires TIME for vibrational energy input (like friction or certain types of uneven heating) to completely thermalize in a system, so that the entropy of this added energy is finally maximized. Thermodynamics isn't very good about describing systems in such flux (unless the thermal energy spreads with minimal temp differences from region to region), because the system has expanded in phase space, but not (even at any "point") to the maximum (equilibrium = highest entropy). So yes, thermo doesn't have much to say about it. Nor does physics has much to say about it, because it's a lot of particles in states that we can't know, and it's just too damn complicated for any theory there is. But I sort of take that as a given. We use thermo for situations where thermo was designed to give answers, and that's in slow processes where equilibrium has been reached in most or all "places." And by "places" I mean in collections of atoms large enough to give a statistical temperature and thus have a heat capacity, as happens even while heat is being conducted through a solid. In engineering, for example, even in problems of conductive heat flow, we pretend that the temperature field T(x,y,z) is composed of points. Of course it is not. It is composed of little bits of matter each of which has enough atoms that allow it to have a well-defined statistical temperature, which means that locally it has reached equilibrium and maximal entropy for the energy it contains. But nature is so fine-grained that in most systems this works like mechanics, with large objects, works without resorting to quantum mechanics.
In QM, as I've noted, thermo gets very much harder and Bolzmann-Gibbs entropy goes over to von Neumann entropy and you do have to worry about wave-function collapse. But that's a separate problem from the problems of large-scale non-equilibrium systems (your shaking bottle, or systems with frictive imputs), these are more like the problems of predicting the weather. There's just too much chaos and information, and we simply need to acknowledge that there is no theory that works. S B H arris 18:08, 16 April 2012 (UTC)
Yes, in a free expansion experiment, you could look at the work done by the gas, and say tha tthis is zero. However, then you ahve chopped up thesystme in subssystems and are looking at the work done by the subsystems on each other. Now, as Reif explains in his book, thermodynamics is misnomer, it should have been called thermostatics, as it only describes systems in thermal equilibrium. But that doesn't mean that it cannot be applied to systems that undergo rapid change. You can derive exact statements using thermodynamics for such processes, like in case of the free expansion experiment.
Of course, such results involve initial and final states that are in thermal equilibrium. But that is a powerful reason not to make the definition of heat and work dependent on the details as SBHarris argues above, because that would make obscure the fact that such a results are rigorous (i.e. it is not conditional on being able to define temperature while the system is indergoing change, which is not possible to do precisely).
Another comment. It is temperature that is defined using the potential of heat flow when different systems are brought into thermal contact. One doesn't define heat in this way. And how would you define temperature if you were to chose this definition of heat (let's forget for the moment that this defintion of heat is problematic)? One can try the high school definition of temperature in terms of kinetic energy of particles, but this is problematic. That definition assumes the equipartition theorem, which isn't valid in quantum mechancs.
Even for classical systems, it won't work, because it would fail to capture a very fundamental aspects of thermodynamics, i.e. that it ultimately derives from an information theoretic description of a system. It is lack of information about the system that makes a thermodynbamic description useful. Entropy is proportional to the number of bits of intormation that you would need to fully describe the exact state of a system, give the macroscopc thermodynamic specification. Now, if you know all the velocities of all the particles, you have a complete description of the system, the entropy is then identically zero. Temperature remains equal to absolute zero at all times, no matter "how hot" the system gets, as suggested by the velocity distribution of the particles.
If you have complete information about a system, you can let Maxwell's demon be effective, it doesn't have to dump its memory (the Landauer bound is thus irrelevant here). The demon knows in advance when the next molecule will come along for which it has to open the gate, by looking up the system specification and doing some computations. This variant of Maxwell's demon is called "Laplace's demon". Clearly this makes any attempt to base thermodynamics on anything other than information theory paradoxical, as what you would get would be vulneralble to such thought experiments involving demons.
What i.m.o. is the big lesson here is that heat, temperature, entropy etc. etc. are to some extent subjective quantitites, that ultimately derive from how we choose to describe a system. In practice, when deriving thermodynamics from statistical physics in the usual way, you encounter this "subjectivity" when defining the Omega function Omega(E), which govesthe number of energy eigenstates between E and E + Delta E. You could say that we should take the limit of Delta E to zero and work with the density of states. However, Omega(E) should be the number of states the system can be in, and Delta E is a finite quantity. If Delta E were zero, you would know which state the system is in, so you would have complete information about the system's microstate. Now when we look at the familiar thermodynamic quantities, like entropy S = k Log(Omega), then it turns out that the Delta E dependence is utterly negligible, and that dependence vanishes completely when taking the thermodynamic limit. Count Iblis ( talk) 02:17, 20 April 2012 (UTC)
It should be plain to any reader that instead of getting better the article is getting worse. For example, there is a "lede too long" tag. While the complaint is technically correct, length is not the operative problem. The underlying reason, which is not confined to the lede, is that both the writing and rationale are incoherent, ill-organised, doubtfully expressed, opaque to the reader unversed in physics, assailable to physicists, and self-indulgent. It certainly is neither encyclopedic in its current form, nor very Wikipedic. No names, no pack drill. At the current rate we will get no further than snapping at each other. This is as nauseating an example as ever I have seen, of trying to see further than others by standing on their toes rather than on their shoulders.
Now, the problem is not that there is a deficiency of available expertise in the subject matter. Nor is it clear that we could rescue the project by having any one person rewrite the whole thing (we certainly could, but how are we to identify the right person?) We definitely cannot do anything constructive in the current dogfight mode. Conversely, we cannot afford to let the existing mess stand as a WP article.
So?
So I am not going to prescribe or even propose what the article should look like, thereby prolonging the exchange of spittle and ink, but I do propose that anyone who wants to go off into a fit of the vapours do so now and let the rest get some work done. He can come back later and sneer if he chooses. Those remaining, I suggest that they leave the article alone for a while, archive most of this talk page, and each go off and work out not proposed text or material content, but a section layout. Then compare their products on the talk page. Given goodwill and flexibility that should not be so hard. The major principle should be that one does not veto material that is neither wrong nor better suited to a different or separate article; instead just put discrepant discussions into separate sections.
Then start rewriting each section till either there is a complete article, or it appears that there is a need to split, add or rearrange sections. Steer clear of editing each other's sections, short of actual error corrections. If one person turns to be writing in engineering terms and another in statistical terms, then put those two topics in separate sections for now. Worry about splitting the article later if at all.
And so on.
When all is done (if ever) either split the product into the right number of articles (if desirable) or call in a reader who is not a physicist but is literate and competent in lay English, and engage him or her to work on it till s/he and friends find it reasonably concise, easy to read and possibly to comprehend, without making physicists' teeth curl. No more of this argumentation about terseness and chattiness. Let's have a bit more competence and a lot less possessiveness. This is not a matter of taste, but of function, and infelicities are not just matters of literary taste, but sources of distraction and confusion. Opinions do matter, but not as a substitute for linguistic skills or hard fact.
And if anyone goes into sabotage mode, the rest of us can go into arbitration mode, and see who is left standing. This damned slanging match should stop. Round about now.
Now, no-one need take this exhortation too seriously, and I know some of us will hate it with all the fury of possessive parents, but when they have finished flinging their plates of porridge from their high chairs, I ask all and any of you: is it any worse than the mess currently in this talk page, or the proud product you see before you in the article? JonRichfield ( talk) 09:30, 18 April 2012 (UTC)
Much of the rest of our definitional problems is a holdout from the days of now-banned user user:Sadi Carnot, who insisted on the purity of usage that heat had to be thermal energy in the act of transfer (thus, heat = heat transfer always), and the very word "heat" even in science, could never apply to thermal energy residing in materials, not moving along a temperature gradient. But there's a residual of usage of heat to mean static thermal energy going back in science a long away, and some of it still remains (as in calling enthalpy "heat content"). Finally, there's a band of people who insist that the purely thermal component of the internal energy of an object or system (which is NOT enthalpy, since it doesn't include mechanical work input or output) can't EVEN be defined, and shouldn't be talked about, even though engineers use the idea all the time (as a differential and change, at least), and use it in their heat capacity calculations in heat transfer. I don't know what to do about these people. When doing calculations, it works. It does not give wrong answers. My opinion is that if it works, it's valid. S B H arris 16:42, 18 April 2012 (UTC)
The heat of a substance or body is the property that gives the sensation of hotness or warmth. Heat is measured by temperature, indicated by a thermometer. A number of different scales have been devised so that thermometers can indicate temperature in a convenient way, usually by the inventors of thermometers. Currently the most used scales are Celsius and Fahrenheit but many have been used down the ages; for some scientific work the Kelvin or Rankine scales is used; these scales have as zero the lowest possible temperature, known as absolute zero; the Kelvin scale has the same size of divisions as the Celsius scale but they are called Kelvins (K); the Rankine scale has the same size of divisions as the Fahrenheit scale the divisions are called 'degrees Rankine' (°Ra).
I suggest that small revisions be highlighted in colour; I tried to put the text in red but failed to find out how to 'do' colour.-- Damorbel ( talk) 08:15, 19 April 2012 (UTC)
Heat and temperature have different physical units, and cannot be connected without using the concept of entropy. Temperature is proportional to the mean kinetic energy of an ensemble of particles in thermal equilibrium; heat is only connected to kinetic energy insofar as it sets the temperatures which cause the energy of heat to flow. The particular type of energy that composes heat is drawn partly from the kinetic energy of particles in matter in thermal equilibrium, but in all real situation such thermal energy is composed of other types of energy as well, which are distributed according to a partition function that varies from substance to substance. S B H arris 17:55, 19 April 2012 (UTC)
we solve such problems with other words that have both common and tech meanings, by having the word direct to the dab page, and have the technical meaning with a paren. Thus, work directs to the work (disambiguation) and if you want the type of work that comes in in joules, you need to go to the technical work (physics) or work (thermodynamics). But heat directs here, since there isn't a heat (physics). Instead, people have insisted on shoehorning popular usages into this article, which otherwise could be a technical one. It's stupid, but there it is.
I've suggested otherwise before, but gotten little support. See above. Want to try this again as a suggestion? That would mean this article would be renamed heat (physics) or heat (thermodynamics). Actually, I think there's enough difference in the really technical thermo term to have a heat (thermodynamics) article where we only discuss heat transfer, and perhaps ALSO a heat (physics) article we could discuss arcane ideas like heat content and what we call the energy that results in heat capacity, when it's not going anywhere (i.e., the isovolemic or non-work component of internal energy change). What engineers often think of as heat (more than just heat transfer, but still measured in joules). That would at least cut down on the lede length, in the science articles. S B H arris 21:06, 19 April 2012 (UTC)
There is a perfectly usable definition of the part of internal energy that is thermal, and that is-- it's the part that has been thermalized, so that it cannot then be withdrawn EXCEPT as heat! That happens immediately to energy you add as heat flow, but it takes time with other types. A very slow compression work is immediately thermalized and immediately irreversible (if you want the energy back, you pay max entropy cost for it). A fast compression generates shock waves that bounce back and forth and take time to thermalize, and during that time, you can get some of your original work back because entropy hasn't increased to the max for the energy you added. Thermal energy is energy that has maximized its entropy for its temperature, by finding all degrees of freedom in the system available to it. That takes time, and I suppose it should thus be noted that the amount of thermal energy that resides in an object, is thus a function of time. But it's a useful concept if you know your timescale.
One of my favorite examples is in the proton spins of ortho vs para hydrogen. At room temp there's enough energy that 75% of H2 is ortho (spin aligned) which is a high energy state, see spin isomers of hydrogen. When you liquidfy the stuff, this should equilibrate to the low energy form, but it takes days to do so-- at first you liquid hydrogen has the same ratios of ortho/para as it did at room temp! The heat the ortho--> para conversion generates is enough to boil the liquid again, so engineers have to use a catalyst to get the extra energy out (thermalize it). Essentially, when you liquify H2 from room temp, the various translational and vibrational modes all go to 20 K, but the spin-temperature stays at room temp for awhile, as though this thermal energy were in an insulated compartment at a higher temp! There's a lovely example of having a kinetic barrier to thermal equilibrium and removal of maximal thermal energy. But it does eventually happen. You can think of it as a sort of slow phase change, and the spin-isomeric transition as a sort of latent heat. But that's not a perfect analogy, since in other phase changes the temperature of the phases is the same. Here, the spin-temp of the H2 is higher than the temp of the liquid, but heat cannot flow by conduction or diffusion. It has to flow in tricky ways to get energy from nuclei into energy of translation of molecules. It is a form of stored "heat" however, as it acts like thermalized energy at room temp, and you can't convert it to work, willy-nilly. The spin isomer energy has equilibrated with thermal energy at room temp, and it acts like themal energy at room temp, even after you've cooled the hydrogen down to cryogenic temps. S B H arris 23:19, 20 April 2012 (UTC)
There have been some recent edits for the term "thermal energy". Chjoaygame ( talk) 03:16, 6 April 2012 (UTC)
On this talk page, one editor put the view that the words 'thermal' and 'energy' could be put together to form the phrase 'thermal energy' as a simple matter of ordinary syntax. This view would make perfect sense to someone who believed in the caloric theory of heat. The caloric theory of heat is not valid in thermodynamics, but it is not a silly theory in that under special conditions when energy cannot be transferred as work or chemical potential energy, but only as heat, as considered by no less a physicist-chemist combination than Laplace and Lavoisier, then quantity of heat transferred obeys the law of conservation of energy. The difficulty for the caloric theory arises when modes of energy transfer other than thermal are allowed. Such revered figures as Carnot and Kelvin were not clear in their minds about this in the early days, until the first law of thermodynamics was well understood. In general such other modes are allowed in thermodynamics; moreover there is no general resolution of internal energy into thermal and non-thermal components; that is part of the import of the first law of thermodynamics.
In tags to proposed edits, another editor puts the view that Wikipedia should effectively ratify the use of the term "thermal energy" because it is sometimes used by engineers. In the lead that he proposes, he argues that the term "thermal energy" is naturally related to heat capacity. In the lead that he proposes, he offers what, at first glance by a non-thermodynamicist, looks like a precise definition of amount of "thermal energy", and offers what looks like a definition of temperature as "the mean kinetic energy [...] of the system". These definitions again would make perfect sense to someone who believed in the caloric theory of heat,and they seem to conform with ordinary language usage. This proposed lead cites page 14 of an engineering text by Incropera and others. The library is closed today and for the moment I must make do with pages from another version of that text from the internet. On page 2 the authors write of "thermal energy in transit". The authors often are careful to write of "the sum of thermal and mechanical energy", and they write of "thermal energy generation". On page 9 they write: "Radiation that is emitted by the surface originates from the thermal energy of matter ...". On page 10 they write: "A portion, or all, of the irradiation may be absorbed by the surface, thereby increasing the thermal energy of the material". They repeatedly use the term "thermal energy" like this on page 10. It seems to me that these are occasions of lapse from sound expression or thinking by these authors, not consistent with their care on other occasions. (Also it is relevant that heat can pass through a surface, which has two dimensions, but can be absorbed only by a body with three dimensions.) On page 16 they write: "the sensible and latent components of the internal energy (Usens and Ulat respectively), which are together referred to as thermal energy." This looks like an explicit definition of "thermal energy" as a component amount of heat in a body. But it also looks like a lapse into the caloric theory way of thinking, because more properly in thermodynamics, sensible and latent heats are defined not as components of internal energy but as components of heat transferred. It is clear enough that we are looking here at special engineering usage, that is not supported by the ordinary line of thinking in thermodynamics.
Perhaps a solution to this would be to put into the article an explicit statement that engineering usage sometimes departs from ordinary thermodynamic usage in ways that could be specified. I would suggest that the lead should only advert to the matter, not detail it or argue for it as is done in the currently proposed version. I would suggest that detail and argument be kept to the body of the article. Chjoaygame ( talk) 03:16, 6 April 2012 (UTC)
The lede now does differentiate thermodynamic use from engineering use. Engineering use doesn't "differ" from thermodynamics (which simply says nothing on the subject in the modern formulation), but rather extends it (breaking internal energy down into components of interest). Thermodynamics is not concerned with many heat transfer situations, such as heat conduction/transfer within solids. So it lacks terminology for what happens there. Engineers and physicists are forced to treat conduction and convection, however, and they need terms of art to do it. In all heat transfer problems, energy conservation IS thermal energy conservation (you can call that "caloric theory" if you like, but it is still true), so the components of internal energy that are thermal and nonthermal need to be identified (or else you cannot predict temperature-field evolution within your system). That is what is happening here, in terminology. "Thermal energy" is a very useful, even essential, term of art in treating thermal conduction and convection.
As to whether thermal energy is "latent heat plus sensible heat" or "sensible heat" alone, it appears from what you've written that Incropora and DeWitt may have changed their minds on this between editions. There may even be disagreements between texts on whether or not latent heat is to be incorporated into thermal energy. If a system has ways of storing or giving up sensible heat, clearly this needs to be taken into account when you do heat conduction problems (for example a microwaved caserole that is full of little bits of ice). If there are no phase changes involved, so that any internal energy changes result in termperature changes, then the sensible heat concept is enough. The point is that engineers need a term for ALL of the part of internal energy that is available if you want to extract heat from the system or object, using a cold reservoir, and this certainly includes both latent and sensible heat. This is called "thermal energy." If thermodynamics has a name for it, please let me know. Clearly a term is needed, and engineers have one. Thermal energy is that term. S B H arris 18:35, 6 April 2012 (UTC)
Chjoaygame, you write:- "These definitions again would make perfect sense to someone who believed in the caloric theory of heat". The term 'thermal energy' was applied by J C Maxwell to the kinetic theory as he developed it, it has nothing in common with the caloric theory. Kinetic theory was developed by Maxwell and others because Lavoisier's caloric theory where heat was considered to be a fluid, simply did not explain many observations such as 'heat is not conserved' and the particle (atomic) nature of matter; there is no possible way to explain quantum effects by caloric theory. -- Damorbel ( talk) 06:07, 6 April 2012 (UTC)
The term "thermal energy" appears in many thousands of books; no doubt many of those uses would be wrong, or unsatisfying, to a thermodynamicist. Yet others are probably used in a more rigorously correct way, where the inability to in general distinguish thermal from other types of energy is recognized, or at least not violated. So the issue is not whether to use "thermal energy", but where and when to use it without being incorrect, or without being significantly incorrect in practice. Dicklyon ( talk) 07:02, 6 April 2012 (UTC)
Dickylon, I know of no places where there is any difficulty figuring out which part of thermodynamic "internal energy" is "thermal energy." Thermal energy by all definitions is the part of internal energy that changes when you add heat to an object, or extract heat from it. It is also the part of internal energy that you can, in theory and practice, extract as heat, using a cold reservoir. That is simple enough, but absolutely essential if you're looking at problems of heat conduction (with heat sources and sinks added), which thermodynamics largely ignores. Conservation of internal energy is not enough to do all heat transfer problems, particularly transient conduction problems: for that, conservation of energy needs to be translated into temperature changes in some way (see heat equation), and in order to do that, you need the concept of heat capacity, or thermal diffusivity of which heat capacity is an essential component. Integration of heat capacity and temperature (plus phase change energy if you have any of that happening) gives an energy term which defines thermal energy, and yet is not internal energy (rather is the part of internal energy that is available to make or absorb heat, even if the heat hasn't been extracted from the object or system, yet). In many problems, if there were no term for this, you'd have to define it mathematically and make up a term. Well, engineers have made up a term! Thermal energy is what thermodynamicists used to call "heat content" (I don't know if they still do or not). But whether or not they do, what is the problem, here? Engineers need a term. So would thermodynamicists if they did engineering heat transfer problems. S B H arris 18:18, 6 April 2012 (UTC)
In response to Comment 2 made by Dicklyon, I would say that it is an issue as to whether we make the Wikipedia appear to ratify the term "thermal energy" as a properly defined technical term or term of art; or whether we leave it as a phrase that can occur in the ordinary language as opposed to as a term of art, which the Wikipedia has no automatic duty to examine. Chjoaygame ( talk) 08:22, 6 April 2012 (UTC)
You can fulminate all you like about what you think WP SHOULD be, but often such opinions fail in the face of seeing what WP actually IS. All that means is you don't have enough experience here. So stick around. You can give your opinions, but as a newb (experience-wise-- just making edits for three years in and of itself doesn't count), we don't really have to take you seriously until you know what you're talking about. It takes 10,000 hours to master any complex subject, and probably that long to really know WP. I'm not even there, yet, and I've 15 times your edits, on a vastly great range of topics, and a lot of arguing on WT. Your 2000 edits, almost entirely on things like Planck's law and thermo topics, and almost nothing in the WP: or WT: namespaces, does not qualify you as to any expertise as to how Wikipedia works. Please try to know what you don't know. If I need to know more about Planck's law, I'll come to you (years ago you might have explained to me why lambda(max) and frequency(max) of the blackbody curve don't multiply to c; but I understand that now). However, when it comes to how WP works and what it is, perhaps you could slap that student sign on your forehead. As we all need to frequently with most areas of our lives.
In any case, thermal energy is clearly a term of art in heat transfer engineering (hell, do you know anyone who uses this in common language?!), and so should be discussed and have an article on WP. If the engineers sometime cannot agree whether to include latent heat in it, that makes it no worse than many another term in science, not all of which are defined by the CIPM or NIST (see weight, where nobody seems to care about ISO). Some terms like matter have even worse definitional problems. This article on heat is nothing special in that regard. S B H arris 18:40, 7 April 2012 (UTC)
Sozbilir
was invoked but never defined (see the
help page).Brookes
was invoked but never defined (see the
help page).