Talk:Thermal conduction

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Opening heading
excuse me, but i'm a freshmen in high school and i have to write about newton's law of cooling. could anyone help me to understand it?...maybe i'm just stupid.....


 * You probably shouldn't try to get all your information here.. Wikipedia is very much a work in progress. Try learning from resources available at your local library. Using the internet as your sole source of information is a very bad idea.CSTAR 18:45, 2 Jan 2005 (UTC)

Heat is transfer of thermal energy. Isn't "transfer of heat" redundant, then?

This probably isn't the absolute best place to get an answer to this question, but where does "q" come from in these equations? There's no "q" in "heat!" I can't seem to find its origin.


 * I think it comes from quantity. (to distinguish from temperature)--njh 04:49, 8 March 2006 (UTC)

incorrect/vague equations
The equations on this page need to be double checked. The first equation presented originally had the heat equal to the gradient of the temperature -- contrary to what the text stated. I will temporarily change the entry so that $$\frac{\Delta Q_{i}}{\Delta t}\sim\frac{\Delta T}{\Delta x_{i}}$$, but the standard definitions of Fourier's law (which is essentially what the above equation is) has some weird notation with the time rate of change of the vector 'heat flux' $$\underline{q}$$ being proportional to the gradient of the temperature: $$\frac{d\underline{q}}{dt}\sim\nabla T.$$ The people over at Heat equation have it going-on, mathematically speaking -- this page should be more rigorous and use derivatives, etc.


 * I agree, furthermore, the conductance part has some mistake, when stating that U=k/deltax, the next expression is somehow wrong, it should be power rather than heat (energy), I'm not english so I'm not editing it. At the end, the Fourier law is repeated, shoud it be merged? Thanks Trufetes (talk) 19:27, 13 December 2007 (UTC)

equations
I'm pretty sure all the vector does is indicate and denote the direction of the quantity. Let me explain. Draw an arrow from the cold region to the hot region. The arrow points in the direction of the temperature gradient. Now, in which direction does the heat flow? That's right, in the reverse direction, from hot to cold. Draw this arrow for the conducted heat flow, and it will be parallel to the temperature gradient vector, but in the opposite direction. I think that's why there is a negative sign in the equation from the Heat_equation page, which says:


 * The Fourier law states that heat energy flow has the following linear dependence on the temperature gradient


 * $$ \mathbf{H}(x) = -\mathbf{A}(x) \cdot \nabla u (x) $$

Note: They use a notation here that is common in textbooks, where bold symbols are vector quantities. Handwritten notation often uses a horizontal line or an arrow, since it's difficult to handwrite in bold. Mikiemike 18:50, 26 April 2006 (UTC)

More equations
I think it's redundant to say "proportional to a constant times something". At the top of the page where it says this:


 * $$ \frac{\Delta Q}{\Delta t} \sim k A \frac{\Delta T}{\Delta x} $$

I think it should be this:


 * $$ \frac{\Delta Q}{\Delta t} \sim A \frac{\Delta T}{\Delta x} $$

Headline text
no good information get more!!!!!!!!!!!!! —The preceding unsigned comment was added by 75.22.15.204 (talk) 15:58, 28 January 2007 (UTC). or,


 * $$ \frac{\Delta Q}{\Delta t} = k A \frac{\Delta T}{\Delta x} $$

Mikiemike 18:50, 26 April 2006 (UTC)

Agreed. The third example is the one I'd use. Ojcit 19:59, 2 October 2006 (UTC)

Fourier's law
This article is a redirect here. Would it make sense to give it its own full article, with maybe a more rigorous mathematical treatment, and leave Heat conduction a more general overview? If Fourier's law doesn't apply to anything else, then the current setup is appropriate. Ojcit 18:37, 19 September 2006 (UTC)
 * Same question with Newton's law of cooling. It must be less popular than his other three, but arguably each of these laws could support a separate article, rather than being subsections of this one.  Ojcit 18:40, 19 September 2006 (UTC)

figure
I think the first figure is misleading. The ΔT line is perpendicular to the wire, which isn't really what we want to show. Likewise, the hypotenuse is unlabled and its meaning is not clear. I guess the fact that Q is the slope of the line T vs. x (i.e. dt/dx) is what the illustrator was trying to get at. If the reader has no experience with derivatives, the picture in its present state doesn't help. Ojcit 19:57, 2 October 2006 (UTC)

Conductance - other kind of stating Fourier
In the subsection "Conductance" this article tells about an alternative way to state Fourier's law. In fact, I didn't find this version anywhere else an I did never hear about it. Is this statement correct? Lskywalker 12:49, 8 July 2007 (UTC)

Newton's law of cooling
Newton's law of cooling really has more to do with convection and radiation heat transfer. How about we give it it's own article and merge it with Heat transfer coefficient? Djd sd (talk) 09:03, 30 January 2008 (UTC)


 * Well, I would say Newton's law of cooling is connected with conductive or convective heat transfer, because it requires heat transfer that is linear in delta-T. That's badly wrong for radiative or processes with a strong radiative component. Really, only pure conduction is fully linear for heat transfer in delta-T, which is why (I suppose) this is discussed here. Perhaps we should write a little qualifier section to make this clear, as you've stumbled on the point, so also will others. Of course, the other main need for Newtonian behavior is slow internal CONDUCTION vs. the rate heat is lost from the surface of an object, but that is covered in the article. However, note that it also concerns CONDUCTIVE processes only-- another reason to discuss it here. I'm open to an entire Wiki on Newtonian cooling, since it's such a peculiar process with so many things required for it to be seen. Leaving (of coure) a main article link and summary HERE. S  B Harris 19:58, 25 February 2008 (UTC)

I agree, Newton's law of cooling should get its own page; it is a phenomenological law including all modes of heat transfer and has no place here on the thermal conductivity page. For the moment I have moved it to the Heat transfer page, in order to clean this page up. Hukseflux (talk) 10:30, 19 March 2008 (UTC)


 * See below in the Newton's Law section. Newton's Law doesn't really have a home now, and needs its own article. S  B Harris 20:33, 8 June 2015 (UTC)

A different question here: Currently it states that "Newton's law of cooling is a discrete analogue of Fourier's law". Is Newton's law discrete? 80.132.30.143 (talk) 07:03, 11 January 2019 (UTC)

Proposal (feel free to adopt).
Heat conduction is a transport phenomenon whereby the energy due to molecular interactions is transferred from molecule to molecule with a corresponding change in temperature. It takes place from regions where the average energy of the molecules is large (high temperature) to regions where it is small (low temperature). In fluids conduction is the result of collisions and molecular diffusion between fast molecules and slow molecules with a corresponding transfer of kinetic energy. In solids there is transport of vibrational energy across a lattice and an additional effect due to (conduction) electrons that behave in a manner similar to the molecules in a gas.

The rate of conduction through a medium depends on the geometry, thickness and intrinsic properties of the medium as well as the temperature difference across it. The most important experimental result describing those interrelations is Fourier’s law of heat conduction, which states that if the temperature gradient $$\nabla T=\left( \frac{\partial T}{\partial x},\frac{\partial T}{\partial y},\frac{\partial T}{\partial z} \right)$$ is small then it is proportional to the heat flux: —Preceding unsigned comment added by Rickproser (talk • contribs) 00:33, 3 January 2010 (UTC) Santa clause cause heat conduction —Preceding unsigned comment added by 58.169.109.226 (talk) 02:17, 18 August 2010 (UTC)

heat
ok i need help with this but i no that this makes heat —Preceding unsigned comment added by 184.88.40.56 (talk) 00:01, 10 March 2011 (UTC)

Heat transfer by radiation
Is is it really easier to handle heat transport through radiation in a liquid as opposed to a solid ? The important factor how to handle radiation is the absorption coefficient. If the material is transparent, radiative heat transport has to be handled separately. If the material is not transparent, the radiative heat transport behaves similar to heat conduction. At least in engineering the radiative heat transport is also included in the thermal conductivity. Things get especially complicated in gases - it only gets easy because gases are often transparent at normal scales. The problem is, that many books just push aside the radiative transport inside condensed mater, though it is not a all simple to separate it form conduction if the material is semitransparent. Materials where internal radiative heat transport is important include typical insulation foams and molten glass. --Ulrich67 (talk) 17:10, 23 December 2011 (UTC)

Conduction (heat) ---> Thermal conduction

 * The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section. 

The result of the move request was: page moved. Vegaswikian (talk) 19:20, 8 November 2011 (UTC)

Conduction (heat) → Thermal conduction – 18:38, 1 November 2011 (UTC)
 * This page should be renamed Thermal conduction for consistency with Thermal radiation and Thermal radiation. I've tried moving it but it came back with an error message. I'm new to moving pages, any help would be appreciated. SSDPenguin (talk • contribs) 09:13, 1 November 2011‎ (UTC)


 * The second page (into which the original page is to be merged) just links back to teh original. I therefore OPPOSE this move, and just suggest that the second page be deleted. --Thehistorian10 (talk) 19:02, 1 November 2011 (UTC)thehistorian10
 * I think you've misunderstood the nature of this discussion. The proposed title is a redirect to this title because they are two different names for the same topic – it should definitely not be deleted. SSDPenguin's proposal is simply to change the title of this article from "Conduction (heat)" to "Thermal conduction" – he/she is not suggesting a merge. Jenks24 (talk) 01:51, 2 November 2011 (UTC)


 * This seems reasonable. Wether my opinion counts or not, i just say move.  - Benzband (talk) 16:53, 2 November 2011 (UTC)
 * The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

'fourier equation'?
The article states the following: "it was recognized that Fourier equation is in contradiction with the theory of relativity because it admits an infinite speed of propagation of heat signals. For example, according to Fourier equation, a pulse of heat at the origin would be felt at infinity instantaneously. The speed of information propagation is faster than the speed of light in vacuum, which is physically inadmissible within the framework of relativity. Alterations to the Fourier model provided for a relativistic model of heat conduction, avoiding this problem." Grammatical errors aside, I was taught to distinguish the term 'Fourier equation' (as the Heat equation) from 'Fourier's law'. Which does it mean here? --Moemin05 (talk) 18:55, 28 May 2012 (UTC)

removed edit that perhaps with a little mor work may be made ok
I have removed a potentially good edit, that as posted contained serious errors, but that perhaps with a little more work may be made ok. The text of the removed edit proposed to differentiate "these functions" but there was in the posted text only one function available to differentiate. The text did not state how it might come to be that $T$ would be a function of $η$; this is a serious omission. There is a missing $d$ in the denominator of one of the derivatives. Perhaps these faults can be remedied. They need to be, to make the edit ok.Chjoaygame (talk) 21:18, 4 May 2013 (UTC)


 * Hey, thanks for noticing those errors. I'll be sure to make those corrections. Is there anything else that you can think of that would improve the edit? Tcox1020 (talk) 00:36, 5 May 2013 (UTC)


 * The problem needs a fairly radical solution. The one just posted doesn't do it. One can't just say 'Oh, let's say this is a function of that' if this is already a function of something else. I don't see an easy way forward here. Perhaps you can find one.Chjoaygame (talk) 03:32, 5 May 2013 (UTC)

Always a new edit should have enough citation of reliable sources to let the reader check it. YOu should give suitable citations.

I am sorry it seems so far you haven't come up with a good way to put in a solution for the rod problem I hope you will keep at it to find a proper way to do it. I think it likely, and reasonable enough, that one has to say that one will make some assumption about the structural form of the solution. An example of such an assumption, for a different case, is that the solution can be factored. For the present case, your solution had an assumption built into it, that $η$ has a suitable form; reasonable. But you needed to put that in with more attention to proper mathematical form. I suppose you will find how to do it in a reliable textbook.Chjoaygame (talk) 04:46, 6 May 2013 (UTC)

*Comment: That might be valuable material and I would not like to discourage the editor, but I really think that it also needs an accessible verbal (as opposed to mathematically symbolic) summary at the head of the section; something like "An important class of heat conduction problems can be usefully described as..." and completed by a verbal summary of the implications of the derivation in the form of a simple qualitative description of the (practical?) implications. As it stands, not one in ten of our readers would give that section a second look. JonRichfield (talk) 07:23, 6 May 2013 (UTC)

undid faulty edit
I have undone a faulty edit. The edit removed the notion of temperature from the lead sentence on heat conduction. The edit replaced the notion of temperature with the notion of "unbalanced energy potentials which lead to an increase in the entropy of the system". Temperature is the factor reported by reliable sources. They do not attribute heat conduction to "unbalanced energy potentials which lead to an increase in the entropy of the system".

We may be seeing here a problem with editor conduct. The edit was not really about thermal conduction. It was about a concept of "unbalanced energy potentials which lead to an increase in the entropy of the system", which is an original research concept being pushed in various places in the Wikipedia by the editor who posted the edit that I undid.Chjoaygame (talk) 11:05, 31 March 2014 (UTC)

Editor Douglas Cotton seems to have begun to use the talk page instead of just posting his innovations immediately as edits. This seems to me to remove the potential problem of editorial conduct mentioned in the just previous comment. This is good.Chjoaygame (talk) 08:19, 1 April 2014 (UTC)

Newton's law of cooling
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.&mdash; MaxEnt 10:48, 10 April 2014 (UTC)


 * Newton's law of cooling (as a behavior) happens in many circumstances, some convective, some conductive. It doesn't happen in transient cooling or heating, or where heat transfer coefficients aren't constant. It deserves its own article as a mechanistic phenomenon, even absent a history section, and it used to have one. Since then, some lumper-editor person stuck it in the convective heat transfer article. Seven years ago it had been moved from the thermal conductivity article to the thermal conduction article here, and eventually the section wound up in convective heat transfer, which is now where the Newton's law stuff still resides inappropriately. It really doesn't belong in any of these.


 * 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, like this one. S  B Harris 19:56, 8 June 2015 (UTC)

Thermal conduction article should be compatible with Second Law article
For reasons similar to those stated in my note in the talk page regarding Heat Transfer, the article on Thermal Conduction should be written in accord with the wording of the Second Law of Thermodynamics which describes entropy increasing towards the state of thermodynamic equilibrium and says nothing at all about thermal equilibrium or heat transferring only from hot to cold. The latter concept comes from the mid 19th century Clausius statement which only applies in a horizontal plane or in a non-gravitational system. That statement is not used by physicists in the 21st century.

Douglas Cotton (talk) 03:06, 1 April 2014 (UTC)


 * It is good to see that Editor Douglas Cotton has now started, as here, to use the talk page instead of posting his innovations immediately as edits. I will continue this comment shortly.Chjoaygame (talk) 08:21, 1 April 2014 (UTC)


 * I have responded] to Editor Douglas Cotton's comment on this subject on the talk page of the Wikipedia article on the second law of thermodynamics. I think it would be redundant for me to talk further here, because the subject matter is largely the same.Chjoaygame (talk) 09:58, 1 April 2014 (UTC)

Common Examples
Can some common examples of thermal conduction be added to the article, perhaps in the introduction. This would help make the article more relevant and less abstract. Thanks! --Lbeaumont (talk) 11:44, 7 October 2015 (UTC)

Conductivity of Gases
Starting editing this article for a class and realized that there should be a distinct section on the conductivity of gases, if not a whole article. I don't have the time right now to come back and make it, but if someone has the time, I wanted to leave a note with a couple of resources:

--Transport Phenomena by Bird, Stewart, and Lightfoot

--http://physics.bu.edu/~redner/542/refs/reif-chap12.pdf

I hope to be able to come back and try my hand at writing the section when I have more time. Rlhota (talk) 18:44, 13 October 2016 (UTC)

error in integrated form of fourrier law
Hello, just saw that in the integrated form of the fourrier law is written as : Q/∆t = -k*A*∆T/∆x However my physic books state it as : ∆Q/∆t = k*A*∆T/∆x With the added delta and without a negative sign. Is it a mistake? Sorry for the bad format as I was in a hurry. 62.203.73.42 (talk) 16:32, 3 October 2019 (UTC) Vincent

Conduction
Heat spontaneously flows from a hotter to a colder body. For example, heat is conducted from the hotplate of an electric stove to the bottom of a saucepan in contact with it. In the absence of an opposing external driving energy source, within a body or between bodies, temperature differences decay over time, and thermal equilibrium is approached, temperature becoming more uniform.

In conduction, the heat flow is within and through the body itself. In contrast, in heat transfer by thermal radiation, the transfer is often between bodies, which may be separated spatially. Heat can also be transferred by a combination of conduction and radiation. In solids, conduction is mediated by the combination of vibrations and collisions of molecules, propagation and collisions of phonons, and diffusion and collisions of free electrons. In gases and liquids, conduction is due to the collisions and diffusion of molecules during their random motion. Photons in this context do not collide with one another, and so heat transport by electromagnetic radiation is conceptually distinct from heat conduction by microscopic diffusion and collisions of material particles and phonons. But the distinction is often not easily observed unless the material is semi-transparent.

In the engineering sciences, heat transfer includes the processes of thermal radiation, convection, and sometimes mass transfer.[further explanation needed] Usually, more than one of these processes occurs in a given situation.

The conventional symbol for thermal conductivity is k 2400:ADC7:1130:8600:6890:F6AE:34A:B623 (talk) 07:22, 20 August 2022 (UTC)