Talk:Heat transfer

message: In the mechanism section many equations and variables are introduced but not discussed in much detail. A couple short sections explaining and highlighting such variables would be beneficial. For example a section which defines heat capacity, discusses how properties of chemicals effect heat capacity, and gives examples of chemicals and their heat capacities.
It also seems as though the mechanism section sets a precedence that there will be a discussion of the math and physics behind much of the material presented throughout the page. However, after the first two sections, equations relating to the material discussed are no longer included. A few specific sections second that could benefit from the addition of equations are:
The heat equation: it is defined and discussed but not included.
Phase change: The discussion of heat of vaporization and heat of formation would enhance section.
The device section: symbols for work and heat are introduced in images but not discussed in text. Maybe include energy balance equation and how it's used.
Llavecch (talk) 09:13, 13 January 2017 (UTC)
thread_title: Discussion of Variables

message: There are many areas where added citations would greatly improve this page. Many of these sections have already been identified; however, the phase change section has quite a few areas that need citations and have not been identified. The introduction could use one right after the main paragraph and mention of the mason equation. The boiling section could use at least two cites considering the length of the section and as of now there are 0 cited sources.
Llavecch (talk) 08:35, 13 January 2017 (UTC)
thread_title: Missing Citations

message: The formula for radiation heat transfer coefficient (in the image showing thermal resistances for each mode of heat tranfer) contains a term for surface area.  This is an error and should be removed.
-mbwittig 10:16, 23 November 2008 (PST)
:I've changed the "Equations for different heat transfer modes and their thermal resistances" image into a wikitable.  Given the age of this comment, I'm not sure if the change above happened, so mine is a literal conversion.  I don't feel like I have the authority to change equations that I don't know/understand, but it should now be possible for you to change them! Sutekh.destroyer (talk) 00:22, 29 March 2010 (UTC)
thread_title: Error found in the picture

message: I've requested a peer review because I think that this article meets several of the Wikipedia criteria for becoming a featured article.  I believe that this article is consise, covers the topic completely, is stable, and contains minimal point-of-view influence.  I believe that this article describes a very complicated topic elegantly, and may be useful for both engineers and people with no engineering knowledge.  If you agree that this article is a good candidate for becoming a featured article, please let me know.  Otherwise, all of use who have worked on this article would appreciate your comments and edits.
Thank you,
-Âme Errante 10:15, 29 July 2006 (UTC)
thread_title: Peer Review

message: 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 19:39, 6 September 2006 (UTC)
thread_title: References

message: Any serious treatment of heat transfer can not ignore phase change.
Kjlgstp 14:27, 29 November 2006 (UTC)
thread_title:  What about phase change? / boiling heat transfer

message: transferring thermal energy from cold to hot is ok, (heat pumps), its only when no work is added, as in conductive, radiative and convective transfers that heat cannot, overall, move to a higher temperature.
also this article says heat transfer is by electrons and phonons only, if this were the case gases could not be conductors, missed out is heat carrying diffusion of any particles (atoms, molecules) in the system.
Asplace 03:09, 2 February 2007 (UTC)
replies: text: Asplace, I think that your statement above, 'transferring thermal energy from cold to hot is ok', is wrong.  Heat pumps do not transfer energy this way, and even with additional work it is impossible.  For instance, the heat pump article states about refrigerators that 'In such a system it is essential that the refrigerant reaches a sufficiently high temperature when compressed, since the second law of thermodynamics prevents heat from flowing from a cold fluid to a hot heat sink. Similarly, the fluid must reach a sufficiently low temperature when allowed to expand, or heat cannot flow from the cold region into the fluid. In particular, the pressure difference must be great enough for the fluid to condense at the hot side and still evaporate in the lower pressure region at the cold side.'  Thus, the work applied actually changes the temperature of the refrigerant by exploiting its physical properties, and at both sides energy still transfers from hot to cold.  It's a subtle point, but it's very important in engineering. As for your second point, you're right on, and I believe this has since been changed. -Âme Errante (talk) 19:07, 7 May 2008 (UTC)
replies: text: Nevertheless Asplace has a valid point.  The first sentence of the article implies that the direction of heat transfer is from hot to cold.  This is true for radiation and conduction but not for convection, at least for laminar flow.  In the case of turbulent flow the turbulence causes mixing which has an averaging effect that resembles conduction, but the mechanism and its statistics are qualitatively different. --Vaughan Pratt (talk) 16:30, 20 June 2008 (UTC)
thread_title:  Major problems with this article 

message: Someone posted this in the article.  Assuming it wasn't vandalism, can someone comment on it or add something to the article?  I've repressed most of what I learned in thermodynamics, and I'm much happier for it.-- joshschr (talk) 21:11, 16 November 2007 (UTC)
thread_title:   ????What about liquid non-metals????also, read the first and second sentences regarding gas???? 

message: Since this is an article that is primarily scientific in nature, I thought someone here might be able to answer it. What is it that causes fire and heat to burn other things. And I mean this on a molecular level. I really have no clue myself, yet it's the only question I've ever had about anything that I couldn't find on the internet. Does it have something to do with the speed that molecules of fire/heat are moving and when this hits say the molecules of something like wood or flesh it separates them or something? Another example would be lasers. Some lasers are fine to hit other objects, they have no visible effect. However a more intense/powerful laser will burn through very hard substances. What is the intense laser actually doing to the substance at a molecular level that the weaker laser isn't. I assume the stronger laser simply has more energy being transferred to the material it is hitting. With human flesh is it a case that it can't properly contain the energy transferred to it, and thus it damages the cells? If so what is it that actually causes the damage at a molecular level, or maybe it would be better to say what is the actual damage at a molecular level? Is it that it breaks molecular bonds or what? Livingston 00:26, 18 September 2008 (UTC)
replies: text: According to skin the epidermis is a tougher outer layer that protects the dermis and subcutaneous tissue.  Presumably the latter are more easily damaged (broken bonds) by a minor burn than the epidermis.  On the other hand inflammation "is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants," and presumably excess heat counts as an irritant.  So I would guess that inflammation could result even from a burn that irritated the dermis without seriously damaging it, in which case redness associated with minor burns could be as much an indication of inflammation as of any serious damage to the dermis.  Not my area, just a guess.  --Vaughan Pratt (talk) 07:42, 5 February 2010 (UTC)
thread_title:  What causes heat to burn things? 

message: "reflectivity = 1 - emissivity" is in fact true when integrated over all the wavelengths (Kirchhoff's thermal law of thermal radiation), but is not true at a specific wavelength.
The wavelength distribution of the reflected energy is the same as that of the incident radiation, but the wavelength distribution of the emitted energy is usually quite different.
This is for instance what explains the greenhouse effect, or the heating of the interior of a car in summer: the window of the car (the gas layer around the earth) is transparent to the incident radiation (which has a peak in its energy distribution at the visible wavelengths, since it is produced by the sun at about 6000°K), while it is much less transparent to the emitted radiation (that has a peak in lower infrared, since it is emitted by the interior of the car or by the earth, at about 330°K).
If the law were true at any specific wavelength, the energy distribution of the emitted energy would be also the same as that of the incident radiation.
The independence on wavelength for the emissivity (gray body assumption) is sometimes used - still, it only means that the dependence on wavelength is neglected for some wavelength band, not that reflectivity = 1 - emissivity in this band.
:True. WP:SOFIXIT SBHarris 08:00, 28 January 2009 (UTC)
replies: text: Not true (so it's a good thing it didn't get fixed).  The greenhouse effect is merely a dependence of absorptivity on wavelength and is not a counterexample to reflectivity+emissivity = 1, which holds even for radiation at a specific wavelength and a specific direction.  This is stated correctly at Radiant barrier#Reflectivity_and_emissivity but incorrectly at Kirchhoff's law of thermal radiation which brings in absorptivity incorrectly (on my list of things to fix).  The statement "If the law were true at any specific wavelength, the energy distribution of the emitted energy would be also the same as that of the incident radiation" does not relate logically to the preceding sentence concerning glass because the incoming insolation and outgoing thermal radiation both originate outside the glass: the glass merely transmits the former from the sun while absorbing the latter from the ground or car interior.  --Vaughan Pratt (talk) 07:26, 5 February 2010 (UTC)
thread_title:  Possible error in the paragraph "Insulation and radiant barriers": assertion that "at any specific wavelength, reflectivity = 1 - emissivity" 

message: I've found nothing about Fourier in this article or in any of the articles bearing on climatology and the various atmospheric sciences.  Why did Fourier invent spectral analysis, a fundamental tool of signal processing, and apply it to his study of heat transfer, if it is so irrelevant to the subject that no Wikipedia editor even mentions it in the context of heat?  --Vaughan Pratt (talk) 18:00, 7 December 2009 (UTC)
replies: text: If it's so important, why don't you put something in the article about it? WP:SOFIXIT. Wikipedia editors aren't omniscient-- we wait for experts to happy by and ask questions like yours. They we point out that it's a volunteer effort, so pitch in. SBHarris 18:29, 2 February 2010 (UTC)
replies: text: It was a question, not a suggestion to add material.  I wish I knew enough about Fourier's contribution to write something on it.  For all I know it is irrelevant.  --Vaughan Pratt (talk) 06:50, 5 February 2010 (UTC)
thread_title: Nothing about Fourier or signal processing?

message: Am I correct in my belief that using non-absolute temperature scales (e.g. Celsius or Fahrenheit) when solving the differential equation given by Newton's law of cooling will lead to errors due to the natural logarithm of the ratio between temperatures? I seem to remember this being the case, but I cannot remember and I cannot find the information anywhere.
Thanks. --137.125.104.76 (talk) 15:46, 2 February 2010 (UTC)
replies: text: No, because the log of the ratio of the temperatures never appears in solving Newtonian cooling problems, or any other cooling problem; heat flow problems tend to be linear in ΔT, due to Fourier's law. You're probably thinking of solving problems like entropy changes in non-isothermal conditions, where integration of dT/T type terms can give wrong answers if absolute temps aren't used. But they're only off by a constant if C vs K is used, because the degree size is the same. SBHarris 18:25, 2 February 2010 (UTC)
thread_title:  Newton's Law of Cooling, solving differential equations 

message: I'm a bit curious whether Convection occurs without 'Work'. Gravity plays a key role and hence there is work, indeed this 'work' is harvested in many ways by many machines?--Rjstott (talk) 17:47, 19 February 2010 (UTC)
thread_title:  Convection and Work 

message: As written, the article misuses the languages of thermodynamics and radiative heat transfer, thus making a muddle of their concepts.
Thermodynamics features a body that is surrounded by a boundary. "Heat" flows through the boundary. "Work" is done on the boundary. The body has an "internal energy." The ideas of heat, work and internal energy are linked by the first law of thermodynamics. The second law of thermodynamics imposes a restriction on the flow of heat, namely that it can flow only from hotter to colder matter. 
In radiative transfer, two or more bodies are said to "radiate against" one another. 
Some of the article's deficiencies are:
* Asserts "Heat transfer is the transition of thermal energy..." but the ambiguous term "energy" is not used in thermodynamics. Could be modified to "Heat transfer is the transfer of heat..." but this would be redundant.
* Asserts "Radiation is the transfer of heat energy through empty space." but this is incorrect for radiation is not a transfer of heat. The correct idea is that when two bodies radiate against each other, heat is transferred from the hotter of the two bodies to the colder of the two.
* Asserts "All objects with a temperature above absolute zero radiate energy..." but the ambiguous term "energy" is not used in language of thermodynamics. To capture the idea of radiative heat transfer it is necessary to introduce the idea that two or more bodies "radiate against each other."
* Asserts "The energy from the Sun travels through the vacuum of space before warming the earth." but the ambigouous term "energy" is not used in the language of thermodynamics or heat transfer. Should be changed to something like "The Sun radiates against the Earth; as the Sun is hotter, heat is transferred to the Earth."  —Preceding unsigned comment added by 99.38.149.90 (talk) 18:36, 28 March 2010 (UTC)
replies: text: You seem to know a lot about it - go ahead, be bold! and edit the article. --Amaher (talk) 22:29, 28 March 2010 (UTC)
thread_title:  Needs edit 

message: how does convection get the heat from one molecule to the next? Grabba (talk) 01:33, 18 May 2010 (UTC)
replies: text: By diffusion (one molecule striking the next), which is also part of all convection. SBHarris 21:09, 28 July 2010 (UTC)
thread_title:  Convection? 

message: Why does the first sentence of this article state that heat transfer is only the transfer of heat by fluids? Convection in gasses, conduction and radiation are treated in the rest of the article.  —Preceding unsigned comment added by 152.74.187.2 (talk) 20:19, 28 July 2010 (UTC)
replies: text: Gases ARE fluids. "Fluids" include gases and liquids. Convection doesn't happen in solids. SBHarris 21:07, 28 July 2010 (UTC)
thread_title:  First sentence 

message: The description on this page is wrong.This sentence has the logic reversed "The point where the added resistance of increasing insulation thickness becomes overshadowed by the effect of increased surface area is called the critical insulation thickness."  It should read "The point where the added resistance of increasing insulation thickness overcomes the effect of increased surface area is called the critical insulation thickness."
For confirmation/explanation, see http://www.raeng.org.uk/education/diploma/maths/pdf/exemplars_engineering/2_SteamPipe.pdf
or a heat transfer textbook.
131.111.85.79 (talk) 13:34, 20 January 2012 (UTC)
replies: text: Replaced cleanup tag with disputed accuracy; as 131.111..; says, it's the exact opposite. Small diameter pipes (or a thin hot wire for example) will lose more heat when a thin layer of insulation is applied. Total thermal resistance is the sum of conductive resistance and convection resistance. The critical thickness is where total resistance reaches a minimum, not a maximum. Should be obvious when one realises that convection resistance can't go lower than zero. Ssscienccce (talk) 03:07, 3 September 2012 (UTC)
replies: text: removed the tag, description seems ok now. Changed symbol for radius to small letter r to avoid confusion with thermal resistance. Ssscienccce  (talk) 11:14, 29 November 2013 (UTC)
replies: text:  Maybe we can move the part to thermal insulation? Prokaryotes (talk) 13:44, 7 April 2014 (UTC)
replies: text:  Moved to Thermal insulation prokaryotes (talk) 00:22, 18 April 2014 (UTC)
thread_title:  Critical insulation thickness 

message: I have re-organized some of the material to try and structure the article a bit better.  I had in mind that this might clarify the contents of this article vs. the contents of Heat.  Not that I necessarily think they must be separate articles, but at least for the time being this may improve the readability.
I also separated out some of the lumped capacitance / thermal circuit stuff to its own article (Lumped capacitance model) as there were bits of that topic scattered in various places and it seemed best to consolidate it there;  this also had the effect of slightly shortening and focusing this article.
Also, Darkside2010, I moved your "multiple issues" section down here as I think it is the norm to add newer comments at the bottom of the talk page (as far as I can tell?)   Hope that is okay.
Dhollm (talk) 10:26, 10 August 2010 (UTC)
replies: text: I further organized the page, made the part on engineering more clear and added some basic aspects missing. Prokaryotes (talk) 13:42, 7 April 2014 (UTC)
thread_title: Organization

message: Please see Talk:Heat#Heat_transfer_physics. Staszek Lem (talk) 18:07, 13 September 2013 (UTC)
replies: text: Added link to overview. Prokaryotes (talk) 13:39, 7 April 2014 (UTC)
thread_title:  [[Heat transfer physics]] 

message: This article on Heat Transfer should not be saying something altogether different from what the article on the Second Law of Thermodynamics says.  The end state of maximum attainable entropy is a state of thermodynamic equilibrium, not just a state of thermal equilibrium.  The latter may not be a state of maximum entropy, unless you define thermal equilibrium as having no further net energy transfers across any boundary between objects and any boundary within objects.  The Second Law says nothing at all about heat transfers being only from hot to cold.  It talks about entropy never decreasing.  All this is well established physics.
Douglas Cotton (talk) 03:01, 1 April 2014 (UTC)
thread_title:  Heat Transfer should be compatible with Second Law article 

message: A  picture in the page says "Red-hot iron object, transferring heat to the surrounding environment primarily through thermal radiation".
I think this sentence is wrong and misleading, in fact if we put our hand near a red-hot iron object like that one showed in figure nothing happens, instead if we touch it we will have a burn. This means that the conduction contribute is predominant. To be predominant the radiant effect the body needs to be at a really high temperature.
Hence I think we can change the sentence in: "Red-hot iron object, transferring heat to the surrounding environment also through thermal radiation". If we want to maintain the word "predominant" we need to use another example instead or we need to specify "at distance", comparing in this way the radiant with only the convective contribution, but also in this case I think we need another example with higher temperature (for example the Sun, that exchanges only radiant heat with the Earth). --Daniele Pugliesi (talk) 10:06, 9 November 2014 (UTC)
thread_title:  Radiant contribute 

message: I would certainly support this becoming a separate page if an editor came along with decent reference works concerning the historical context of Newton's investigations.  I didn't find a lot in a quick search.  I did find one PPT which claimed that Newton used a modern-style thin tube thermometer filled with linseed oil, marked in a "Celsius" scale (perhaps centigrade would be the more correct term).  It also pointed out that Newton's law is correct even though his own experiment disagreed, due to experimental effects such as convection within the thermometer itself.  It wasn't up to cite-worthy standards, though.  It seems Newton himself only regarded his law as valid for temperature differences up to 10 degrees C.— MaxEnt 10:48, 10 April 2014 (UTC)
replies: text: Newton's law of cooling happens in many circumstances, some convective, some conductive. It deserves its own article as a mechanistic phenomenon, even absent a history section, and it used to have one. Then some lumper-editor person stuck it in the convective heat transfer article. I'll give everybody a few days to comment, and then assume that silence implies consent, start a Newton's Law of Cooling article, then spin this section off per WP:SS, leaving a small summary section behind. That needs be done also, referencing this "law" in several other heat transfer articles. SBHarris 19:56, 8 June 2015 (UTC)
thread_title:  Newton's law of cooling 

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thread_title:  External links modified 

message: The article needs cleaning up. Heat is not a fluid, it does not "flow".Damorbel (talk) 16:32, 1 January 2021 (UTC)
thread_title:  Heat Flow. 

message: Hi. Isn’t the phrase “heat transfer” redundant, since “heat” is defined in thermodynamics already as energy being transferred by mechanisms other than work and transfer of matter? Alej27 (talk) 00:13, 4 November 2021 (UTC)
replies: text: It is the commonly used term in the field. Just look at the names of the references and external links. Meters (talk) 00:17, 4 November 2021 (UTC)
thread_title:  Isn’t “heat transfer” redundant? 

message: .[8] An example of steady state conduction is the heat flow through walls of a warm house on a cold day—inside the house is maintained at a high temperature and, outside, the temperature stays low, so the transfer of heat per unit time stays near a constant rate determined by the insulation in the wall and the spatial distribution of temperature in the walls will be approximately constant over time.
This does not take into account the dew point of the walls. A better example could be found. 86.150.117.77 (talk) 17:52, 5 October 2022 (UTC)
thread_title:  Dew point 

message: I have restored the History section, but moved it to the end of the article so as to deemphasize its importance. I agree with Sgubaldo that a History section is not really necessary, but I think it would be nice to have one. At the end of the article it will hopefully offer minimal distraction. As for now the section is woefully inadequate and unbalanced (my fault) consisting mainly of a long, quote-heavy account of just one series of experiments by Benjamin Thompson and subsections copied from other parts of Wikipedia. Some little editing has been done to the latter though, while leaving them mainly unchanged at their original pages.
The relevant parts of the History section could be moved to the articles Thermal conduction, Thermal conductivity, Convection (heat transfer), and Thermal radiation respectively, and I might try that if it is not suitable here. I was thinking of adding historical content to Convection (heat transfer), but found that there were two seemingly overlapping articles: Convection (heat transfer) and Convection; the former more relevant on account of its title, the latter—in my opinion—better and more complete. I wasn't sure where best to put it.
If some senior editor feels there should be no, or just a brief History section, I'll leave it at that. For all I have to offer is expansion. Unfortunately, I don't have time to scour the literature for a nice, balanced section covering all different time periods. My additions must rather happen as I come across them for other reasons, meaning—for now—few and far between additions of more Thompson and other 17th and 18th centuries investigators. The Cosmic Ocean (Please feel free to modify or undo any of my edits as deemed appropriate.) 16:07, 16 January 2024 (UTC)
thread_title:  Restored the History section