Talk:Heat/Archive 1

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Heat flux

Should't it be "heat flux density" instead of "heat flux" for W/m2? At least that's what NIST is telling me [1]. But there seems to be a lot of confusion about the terms. -- Andreas Hartmann

"Heat flux is defined as amount of heat per unit time per unit cross-sectional area, is abbreviated q, and is measured in watts per meter squared. It is also sometimes notated as Q″ or q″ or ."

What does that mean? Is there a typo in that?

Brownian motion

Where would brownian motion fit in here?

I'm not sure this would be an appropriate place to discuss brownian motion. While brownian motion is certainly a heat induced phenomenon, it is not really a principle characteristic of heat and introcuding it here would likely distract from the main topic at hand. --Matt Stoker

I agree. Brownian motion occurs even when everything has reached equilibrium temperature.

Heat, on the other hand, has something to do with 2 bodies at different temperatures.

Then there's always Judge Joe Brown, who propbably deserves the last say on the matter.--Achim 22:11, 18 June 2007 (UTC)

latent heat

What, no mention of latent heat?

There is so much that could be added. If you want latent heat, please add it! Heats of reaction would also be useful if anyone has the time.--Matt Stoker

---

Is condensation really a separate form? I guess since convection is a separate form it might be. If so, are there others we're missing? - Omegatron 02:00, Aug 23, 2004 (UTC)

Forged iron picture

That's a nice picture (the forged iron). Collabi 08:47, 23 August 2005 (UTC)

Its from User:Fir0002, one of Wikipedia's more prolific photographers. You might like to check out his gallery of other photos. -- Solipsist 17:52, 23 August 2005 (UTC)

The caption for this picture reads: Heat emanating from a red-hot iron rod. Is this not misleading as what the viewer is seeing is light emmission? Maybe it should be rectified in some way?

Radiation

I don't know where Radiation is supposed to link to but right now it only links to a redirection page. Then, when i click on thermal radiation (which I would figure it is) i get to something about the black hole. -- Dennis Schaaf

It links to thermal radiation now. It looks good to me. --DavidCary 00:29, 19 January 2006 (UTC)

Definition

'Heat' is a term we use to quantify the internal energy level of given matter relative to a reference. All matter has the ability to interact with electromagnetic radiation (a.k.a light, radio etc). The properties of the matter as well as its physical structure dictate how that interaction occurs. For instance, if matter (human skin for instance) 'absorbs' ultraviolet http://en.wikipedia.org/wiki/Sunburn yet 'radiates' infrared we use terms like 'it gives off heat'. Really however it is simply converting one form of energy to another while attempting to maintain thermal equilibrium with its environment. (Thankfully this is the case, otherwise the suns 'heat' would do us little good)

http://dictionary.reference.com/browse/heat Item #7

-- Harvey W. Gramm

Heat is a term we use to quantify the energy level of given matter relative to a reference.

Really? I thought that was temperature?

while maintaining thermal equilibrium with its environment.

I'm confused. Human skin, the sun, and the room I am in are all at *different* (non-equilibrium) temperatures, right?

--DavidCary 00:29, 19 January 2006 (UTC)

ISN'T EVERYONE OVER COMPLICATING THIS!?! Nasa says Temperature = average motion of molecules in stuff. Cold stuff = organized molecular stuff. Hot stuff = disorganized molecular stuff.

...Am I wrong? Can I change the definition to meet my simple yet concise answer? The current entry seems way over complicated IMHO. --User:8r13n 21:38, 19 January 2006 (UTC)

Your definition applies most probably to temperature. Heat on the other hand is the amount of energy that's being exchanged as an effect of differences in temperature. One more thing -- heat can be exchanged between "stuff" that's not necessarily made of molecules. One good example is the energy exchange between the Sun (made of plasma) and a grain of table salt (made of ions) on your pretzel at lunch. --Unconcerned 05:10, 22 January 2006 (UTC)

Ok, so maybe I should have said, "motion of atoms OR molecules." Honestly it doesn't matter. I changed the page because the previous description was too verbose and complex. This is an encyclopedia for everyone not just a textbook for math geeks.

...I feel my simple definition is important because heat is something everyone wonders about at least once in their life. Some people may never bother look it up. Others might just punch it in Wikipedia and check it out. If our page is too complicated they will give up and learn nothing. I had that experience. Lucky for me the second link on Google took me to Nasa's site. They make a point of explaining things simply. What if the reader is only 8 years old? We have LOTS of young people online.

I have changed the main page again. I left all the existing text and only added a simple explanation for regular people just above the confusing gibber-gabber. I did this because I think concepts are key. We might not be able to get the average reader to understand everything about heat and exactly how it works but if we can at least get the idea across we'll have done something great. NASA seems to agree with me and I hope you will also.

In closing I'd like to add that I have a huge amount respect for those of you who take the study of science seriously. This world wouldn't be the same without you guys. I hope no-one is offended by my strongly opinionated amateur perspective.

--User:8r13n 13:43, 22 January 2006 (UTC)

Thanks for you candid comment, 8r13n. You are probably right-- it looked quite insipid. Please take a look at the intro and feel free to improve. Regards! --Unconcerned 00:02, 23 January 2006 (UTC)

Saying that "Heat is a form of energy" is wrong. Heat is not energy. Heat is not a form of energy. Although I'm no physicist, I know that there is a common misconception about heat. In order to back what I'm saying, just search Google for "heat is not energy" and "heat is not a form of energy". In the top 10 results for both searches, there are even several university websites that state this fact. Strictly speaking, heat is not energy. Even though the page has to appeal to all audiences, the first sentence still needs to be technically correct. I think this first sentence should be changed to say something like "heat is the term to describe a type of energy transfer". I'm not going to make this change at the moment, because it seems like you all have been having this discussion for a while now. I don't want to barge in... --Endeavor 20:43, 24 February 2006 (UTC)

Endeavor, in thermodynamics and engineering, heat is as much a form of energy as mechanical work is ;-). Views are in disagreement, as are college textbooks and .edu websites. Mathematically, at the macroscopic scale, heat and work are both the result of a system's transition from one equilibrium energy level to another. However, the article is not titled Heat (Classical Thermodynamics). Classical thermodynamics doesn't give any further detail about the process. Microscopically, both quantities have to transfer outside the system, and that transfer equates into net energy changes in the system's boundaries and surroundings, particle by particle. That is, they both convert back and forth into energy during the transfer. Since we can't normally equate apples and oranges (read that: energy and "not energy",) it is quite natural to consider heat and work as (transient) forms of energy: they don't actually exist at equilibrium but they help us calculate the amount of energy transferred. Let me know if this doesn't make sense. --Unconcerned 08:20, 25 February 2006 (UTC)

I guess it kind of makes sense. So when would one say that heat is not energy, and when would one say that heat is energy (and be technically correct both times)? --Endeavor 18:13, 1 March 2006 (UTC)

Guess it depends who you are talking to. --Unconcerned 05:23, 2 March 2006 (UTC)

Perhaps it best to think of 'heat'(term) as the difference(quanitification) in temperature(internal energy level) between one body and another(reference).-- Hwgramm 19:30, 18 February 2007 (UTC)

The definition of Heat as a "transfer" of energy seems confusing. We don't say "heat takes place between body X and body Y", we say "a heat transfer takes place or simply heat is transfered between X and Y". Is it really not that Heat = Thermal Energy as an uneven oscillation of particles of Matter? Furthermore, is it not that Thermal Energy = Kinetic Energy ultimately as a change of Matter from one state to a more uniform one (in terms of the relationship between its particles)?--Lucian 22:08, 9 September 2005 (UTC)

I agree. Many people explain heat pumps and other things using caloric theory. Unfortunately, caloric theory, while it seems to give a good explanation for most things, is not quite correct. Even worse, people trying to explain heat pumps using the more modern theory often make explanations that are confusing or incomprehensible.

I think a big part of the confusion is that what we used to call "heat" in caloric theory is now described by 2 very different things:

• the "heat in one object" --> the kinetic energy of all its atoms, relative to the "average" velocity of the object.
• the "heat flowing from one object to another" --> the net energy (in the form of photons? in the form of atom collisions?) flowing from one object to another; the energy in the photons from the hot object to the cold object, minus the energy in the photons from the cold object to the hot object ... but typically considered something different from "light" (especially monochromatic light) or "radio waves" or macroscopic kinetic energy.

I hope you agree that, if I place a lump of metal on top of a block of ice, the "kinetic energy of the atoms in the block of ice", the "kinetic energy of the lump of metal", and "the energy the flows from one to another" are not identical, even though they may all be measured in Joules.

Is there a short, but not misleading, name for each of these 2 different things? Or should we continue to call both of them "heat" (or perhaps "thermal energy"), and assume our reader is brilliant enough to figure out which one we meant in context? --DavidCary 00:29, 19 January 2006 (UTC)

There is. Check out enthalpy. --Unconcerned 16:34, 19 January 2006 (UTC)

I think we should have different names for the two and we certainly can't continue to call them both "heat." Thermal energy is a good suggestion to replace "heat in one object." The latter notion was discarded with caloric theory; heat is not a property of a system that flows like a fluid to a second system. The other sense of heat is the one we should keep, i.e., the transfer of energy between two objects having different temperature. The third sentence of the Heat article:

Heat can be transferred between objects by radiation, conduction and convection.

would be better if it said heat is the transfer of energy between objects by radiation, etc. To distinguish energy transfer by heat from that due to work, we could note that heat is a transfer of energy that does not require a change in external parameters such as volume (Baierlein p.2). This might be too complicated at the outset. I agree with those who want the article to begin in an accessible manner, but I think some refinement is still needed.--PotomacFever 11:28, 22 July 2006 (UTC)

Heat wave

I suggest add information about heat waves

Thermodynamics

Thermodynamics is not a theory. Thermodynamics is a branch of physics studying energy and energy transfer. And there are laws of thermodynamics, not theories. While there are specific theories within thermodynamics (statistical theory, kinetic theory), they should not be conflated with thermodynamics itself.--John^DO|^{Speak your mind} 04:07, 25 January 2006 (UTC)

SI Units

Unless I'm missing something, could the proper SI units of mass, kg, be included instead of pounds? This page may be edited and read by Americans, who use imperial units, and I know the principal of latent heat is the same for everybody- but as a science based article I think it should be standardised to SI units.

Heat definition (continued)

I notice the above debate/discussion as to the definition of heat. I collect books and textbooks on heat. The book I bought last week was James Clerk Maxwell’s 1871 classic Theory of Heat; I own more than 50 such similar books. Generally, from my readings, the most succinct definition of heat to be found is:

Heat is “energy in transit”

You can derive this definition via summation of the following sources:

• In a thermodynamic sense, heat is never regarded as being stored within a body. Like work, it exists only as energy in transit from one body to another; in thermodynamic terminology, between a system and its surroundings. When energy in the form of heat is added to a system, it is stored not as heat by as kinetic and potential energy of the atoms and molecules making up the system.

• The noun heat is defined only during the process of energy transfer by conduction or radiation.

• Heat is defined as any spontaneous flow of energy from one object to another, caused by a difference in temperature between two objects.

• Heat may be defined as energy in transit from a high temperature object to a lower temperature object.

• Heat is an interaction between two closed systems without exchange of work is a pure heat interaction when the two systems, initially isolated and in a stable equilibrium, are placed in contact. The energy exchanged between the two systems is then called heat.

• Heat is a form of energy possessed by a substance by virtue of the vibrational movement, i.e. kinetic energy, of its molecules or atoms.

Yet, if anyone wants to blend these definitions into the article, then by all means do so. Also, if anyone wants to do a more advanced definition of heat, possibly as sub-section to the heat article: of the 16 fundamental particles of the universe, Noblest Martinus Veltman, in his ’03 book Facts and Mysteries in Elementary Particle Physics, defines the 4 particles with integral spin to be the “energy” portion of the universe and those 12 particles with ½ integral spin to be the matter portion of the universe, approximately. Hence, in this manner, heat can be defined as either gluon, photon, boson, or graviton transit or exchange. For this definition, however, I have no source (I am still in the process of digging around for it).

References

Please feel free to comment.--Sadi Carnot 01:43, 3 March 2006 (UTC)

Agree. Excellent contrib. --Unconcerned 04:30, 3 March 2006 (UTC)

Congratulations. I suggest to fit Sadi's text in the main article, as a new topic as Heat definitions 132.203.32.206 02:01, 10 May 2006 (UTC)

My suggestion plz extend the def.

Heat is the energy in transit within or out of system.Holywarrior 12:06, 3 July 2006 (UTC)

I think the article needs to be revised per the above definition of heat, but I'm not comfortable just doing it without first posting some discussion. There are still passages in the article that treat heat as a property of a system. A good (bad) example is Thermodynamics. There the use of the symbol $\Delta Q$ is a mistake, since heat is not a state function having initial and final values. (However, it would be correct to use lower case $\delta Q$ in the differential expression for heat.) The offending $\Delta$ belongs further down in the Thermodynamics section in the equation :$q=U-w\$, which should be :$q=\Delta U-w\$ (Baierlein, p. 10, equation 1.11, though he denotes internal energy by $E$ in place of $U$. Continuing with the same instance of $\Delta Q$, removing the $\Delta$, the equation

$Q=\int _{T_{0}}^{T_{f}}C_{p}\,dT\,\!$

is true but only for constant pressure (Baierlein, p. 12).--PotomacFever 10:59, 22 July 2006 (UTC) FURTHER NOTE: I reverted the edit someone else made to my posting since the differential expression for heat can be inexact or exact (see Reif, Statistical and Thermal Physics, p. 83). Heat is an instance of a Pfaff differential expression, discussion of which is beyond what we need but which can be found in Chapter II of Herman Reiss, Methods of Thermodynamics. --PotomacFever 11:23, 26 July 2006 (UTC)

Why don’t you start up a new header in the article: “Exact differential vs. Inexact differential forms of heat” so to explain these subtleties. I have the Reiss & and Baierlein to give it an overview when it’s done. --Sadi Carnot 15:01, 26 July 2006 (UTC)

Heat definition a semantic issue?

I was very surprised to see many references to heat as 'thermal energy in transfer', as a physicist with 20 years kicking about general science i'd always thought it was just 'thermal energy' and that defining temperature clearly was actually more of an issue. but having read all the wikipedia entries around this, i started to wonder if its a not just really a language issue. when used with a formula a word can get a clearer definition, english definitions rarely match the rigour of a scientific one's, and science, has over the years, slowly moulded the english definitions of words, i'm thinking that 'heat' still has a gap between definitions, and the reason it hasn't been clarified is that its being pulled between two scientifically different ones, we are at a stage in the evolution of the word 'heat' where it has two meanings, one best aligned with use as a verb and one with use as a noun, as a verb it is all about 'doing' a temperature increase, as a noun, which is where scientific use has most affected the meaning, it has become 'thermal energy'.

so, heating is the action of increasing the temperature of something, (cooling as negative heating) a heater is a thing that causes an increase in temperature (cooler causes a drop in temperature), whereas heat is more scientific as in, adding heat might not cause a temperature change if, for example, you are in a phase change, and heat can be exchanged without a change in temperature, making it clearer that thermodynamic equilibrium is a balanced exchange in heat. (also heat as a noun has no inverse/reverse.) Asplace 14:01, 3 February 2007 (UTC)

Thank You. I agree it is just a matter of semantics. Hence my opening statement that heat is a term. We all use it if not daily, probably weekly. We hear phrases such as "This room needs more heat" or "That runner looks overheated", "Come in out of the heat", "Can you heat up my food?" etc. Because of the arbitrary nature of the term 'heat' it is doubtful that the noun will ever become more than it is - a relative term. An ice cube has heat relative to liquid nitrogen for example. So in this case 'heat' is a term that quanitizes the difference in temperature between two things. The verb on the other hand: "to heat" is like you say, increase the temperature of something.--01:43, 13 February 2007 User:75.83.209.22 (Talk) (Harvey W. Gramm)

I would be hesitant to define heat as anything other then what it technically is. This article that I found makes the definition of heat very clear. I would like to see someone more familier with this site to somehow bring it into the wiki.--ZN 23:01, 12 March 2007 —The preceding unsigned comment was added by 199.74.83.195 (talk) 04:03, 13 March 2007 (UTC).

Heraclitus quote

The quote at the end of the first paragraph of the history ("All things are an exchange for die") seems bizarre -- did some prankster change it? --Harold Kyriazi

Fixed (it should be the word "fire"); thanks:--Sadi Carnot 05:15, 25 July 2006 (UTC)

Can heat be made to flow from cold to hot?

Shouldn't we change the:

"Heat can only be transferred between objects, or areas within an object, with different temperatures, and then only in the direction of the colder body (as per the Second Law of Thermodynamics)."

to

"Heat can only transfer itself ..."

In the present state it indicates that it is impossible to transfer heat from a cold source to a warm source. What is a heat pump or a fridge then? It seems to me that heat only can't transfer itself spontaneously from a cold body to a hot body. Or does this interfer with the discussion if heat is only to be seen as "energy in transfer" rather than "energy"? User:TomTompa 08/06/06

This is just a technical detail. If we want to move heat in the other direction, e.g. refrigeration, we have to add energy to the process in the form of work. See: second law of thermodynamics for clarification. Thanks:--Sadi Carnot 18:55, 7 August 2006 (UTC)

Other heat transfer mechanisms

I think the two "other heat transfer mechanisms" are somewhat misplaced. Latent heat is not a heat transfer mechanism, it is a property that can be used to enhance heat transfer, but ultimately the heat transfer happens by one of the other three. A heat pipe is not so much a mechanism as a device that utilizes the other three mechanisms.

In fact, I think this article could be severely cut back to maybe the first four sections. Heat transfer and latent heat already have their own articles and the "heat dissipation" section doesn't really fit at all. Having just stumbled across this page I don't want to make such big changes without throwing the idea out there first though.BCAttwood 18:12, 21 August 2006 (UTC)

References

I´ve been doing some search for information in this subject and found a couple of available textbooks on the internet that will surely be usefull for expanding and also refining the concepts of heat transfer.

Please look at:

A Heat Transfer Textbook, John H. Lienhard V, Professor, Massachusetts Institute of Technology.

• http://web.mit.edu/lienhard/www/ahtt.html

Wolverine Engineering Data Book II, Dr. K.J. Bell and A.C. Mueller:

• http://www.wlv.com/products/databook/databook.pdf

Wolverine Engineering Data Book III, Pr. John R. Thome:

• http://www.wlv.com/products/databook/db3/DataBookIII.pdf

Please comment what you think. WiKimik 19:49, 6 September 2006 (UTC)

Sun heat image

User:Deglr6328, who states: “this picture is indeed quite wrong. you are looking at the super-deep UV (near x-ray) emission of highly ionized He in the corona in that image. thats not where most of the heat from the sun comes from” and User:128.151.43.177, who states: “WRONG image is taken in the deep ultraviolet range well beyond the thermal EM blackbody emission”, have problems with the “red” sun image (right) and want the “yellow” sun image (left) used in its place:

File:SOHO solar flare sun large 20031026 0119 eit 304.png

Solar-thermal "heat" emissions recorded via the SOHO/EIT telescope.

The photosphere of the sun is 5800 kelvin and radiates immense amounts of visible and infrared electromagnetic radiation (blackbody radiation).

I feel the yellow image has little visual impact. Until someone adds a reference stating that heat is defined only for certain frequencies, I will replace the yellow photo for the red one. Red is associated with heat more so than yellow. Thanks: --Sadi Carnot 03:01, 28 November 2006 (UTC)

am i an idiot?

i have no idea what you mean with 99% of this stuff because (im not fully iduicated and don't speak the hole langauge im swedish...) but i thought that warm/heat is starting to be stuck in the atmosfar and that our earth is only getting warmer for each year we let out (car gases etc etc etc) and that in some wile it will be so warm that the artic pools are starting to melt (that means were gonna have a pritty nice flood soon :( but but) and that we almost cannot stop it. oh well but i saw a show about space it says: if your inside the light (from the sun that means) it was (some warm level) and if you were in the shadow it was almost 0 kevin (i don't remmeber the exact number sorry) and that their space suits had to stand that warm and that cold. so... how the hell can the sun "beam" travel thought the space and not get cold on the way? it doesn't make any sence, right? please help me with this problem as fast as possible becuse i got a school work on this, and i can't understand this.

To answer your first question, yes.

Red hot iron

A red-hot iron rod from which there will be a high rate of heat transfer, primarily through radiation.

The thumbed image claimed red hot iron had fast heat transfer due to radiation. Though red iron glows, the heat transfer is very slow from radiation alone. The quickest way to transfer heat is through conduction (i.e. touching). If this is wrong, feel free to correct my edit, but I'm fairly certain this is the case. falsedef 23:20, 17 March 2007 (UTC)

Completely wrong I'm afraid (in a gas anyway). Do the sums, but how do you think electric bar fires (or coal fires for that matter) workMAG1 00:11, 18 March 2007 (UTC)

Electric bars aren't fire. They conduct heat by touching the cookware to the iron itself. They produce resistance, which creates heat on the metal. There's some convection and radiation, but radiation is the lowest of all those. You can easily place your hand near glowing iron. Touching is when you actually receive enough heat to burn yourself.falsedef 09:07, 18 March 2007 (UTC)

Alright, I found a source: "Cooking on the stovetop utilizes conduction through a pan to heat the contents. In dry heat cooking, heat is conducted directly from the pan to the food, as shown in Figure 2.1. The heat is generated by resistive elements on electric stovetops." [2] In absence of a conductor, radiation might become the primary heat loss. I'd need to see a source for iron having "high rate of heat transfer" through radiation. falsedef 09:52, 18 March 2007 (UTC)

You are mixing two things up. The point of heat transfer is that you are transferring energy from one body to another or the surroundings. yes, if you stick a pan on top of a hot piece of iron then the primary mode of heat transfer will be through conduction; however, that is not what is shown in the picture where there is an isolated piece of red hot iron transferring energy to the surroundings. The heat transfer coefficient to air will be small (owing to the low density of the air) and so if you place a body, such as your hand, close to the poker but not touching it, the primary mode of heat transfer will be through radiation. If you touch it then of course conduction will become dominant and you end up with a burnt hand. However, as shown in the picture, the only thing touching the hot part of the metal is air, and the caption is true (and this actually is what your reference says). The whole point of the picture is to illustrate the connection between temperature and radiation. You can do your own sums: you want the Stefan-Boltzmann law for radiation, and it shouldn't be too difficult to track down a heat transfer coefficient for combined conduction/convection to air (ignore geometry to get the right magnitudes). The standard text is Engineering Thermodynamics: Work and Heat Transfer by G.F.C. Rogers & Y.R. Mayhew. MAG1 11:22, 18 March 2007 (UTC)

That's not a high rate, though. A high rate of heat transfer would need to be done through conduction. You can label it as the primary heat transfer in gas, but it's not high rate. When insulated, iron takes a long time to cool. No one uses hot iron rods as a radiative heat source. When radiation is needed for high heat transfer, then a filament like nichrome is used. The current text looks fine, though. falsedef 22:58, 18 March 2007 (UTC)