Talk:Thermal diffusivity

message: There's apparently at least 3 kinds of diffusivity, including thermal, mass, and momentum.  I'm thinking thermal shouldn't get a monopoly on the subject.  (I don't have the expertise to be sure). Ojcit 17:21, 2 October 2006 (UTC)
thread_title:  redirect appropriateness 

message: I think it is a measure for how fast the heat (or actually the standard deviation of the heat) spreads from a certain point, shouldn't this be mentioned somewhere? (Unsigned)
It is a measure for how fast temperature (in Kelvin) spreads within a certain material at a given temperature. The heat (in Joule) spreading measure is actually thermal conductivity. E.g. copper has a higher thermal conductivity but a the smaller thermal diffusivity than gold http://de.wikipedia.org/wiki/Temperaturleitf%C3%A4higkeit, i.e. copper can transport the same amount of heat faster than gold, but heats up less. Nontheless, I agree with the idea of adding a non-academic discriptive explanation. Filousoph (talk) 05:34, 14 May 2012 (UTC)
replies: text: In particular the thermal diffusivity is in my view not "how cold a material feels", as written in the introduction. If I take a material with very high diffusivity but low density and low cp, it will not feel cold since the low density and low cp surface will reach quite fast the skin temperature. If it feels cold, it has to remove heat from the skin, so the thermal conductivity is decisive --Eio (talk) 08:47, 11 November 2016 (UTC)
thread_title:  explanation 

message: Symbols \kappa and k for thermal diffusivity and thermal conductivity look very similar, and k is widely used for almost any coefficient. I suggest to use D and \lambda instead. The formula would be:
D = {\lambda \over {\rho c_p}}
 {\alpha}  is widely used for Thermal diffusivity --pR@tz (talk) 15:39, 15 March 2008 (UTC)
replies: text: I don't know about the rest of you, but although kappa and k look alike, I see kappa way more than alpha for thermal diffusivity. Should it be changed back? Awickert (talk) 22:37, 9 December 2008 (UTC)
replies: text: Come to think of it, I've never seen alpha for thermal diffusivity, but have seen it many, many times as the coefficient of thermal expansion, which (if this is the dominant usage) could cause confusion. Awickert (talk) 22:39, 9 December 2008 (UTC)

text: I suggest to skip k and \kappa for the denotion of thermal diffusivity, because in the formula below they are already used for thermal conductivity. To me that seems contradictory. Stonovic (talk) 14:32, 23 February 2012 (UTC)
thread_title:  Symbol usage 

message: I like how the table of thermal diffusivity values lists them in random order, and duplicates the entry for air.  — Preceding unsigned comment added by 71.103.149.123 (talk) 06:34, 12 September 2011 (UTC)
thread_title:  table of values 

message: That would make sense?131.211.151.19 (talk) 12:49, 14 March 2012 (UTC)
thread_title:  Why not a table of k??? 

message: Doing a simple unit analysis of the definition given in the first section of this page suggests /something/ is off. Not sure what (I haven't had a chance to look into it), but ( W / (m^2 K) ) / ((kg / m^3) (J / kg K)) comes out to m / s, not the m^2 / s listed as the SI unit for thermal diffusivity in the end of the first paragraph.  — Preceding unsigned comment added by 99.224.222.199 (talk) 20:15, 8 February 2014 (UTC)
thread_title:  Unit analysis 

message: Substituted at 08:33, 30 April 2016 (UTC)
thread_title: Assessment comment

message: That's just wrong. Effusivity is related to whether a material is cold to the touch or not, not diffusivity. A material with negligible heat capacity immediately assumes the temperature of the body and therefore does not feel cold or hot, even though it has a diffusivity which is enormously larger than e.g. aluminum.  — Preceding unsigned comment added by 157.193.65.173 (talk) 11:17, 13 February 2017 (UTC)
thread_title:  "It is approximately analogous to whether a material is "cold to the touch"[citation needed]"