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| In [[heat transfer]] analysis, '''thermal diffusivity''' (usually denoted ''α'' but ''a'', ''κ'',<ref>{{cite book|last=Gladwell|first=Richard B. Hetnarski, M. Reza Eslami ; edited by G.M.L.|title=Thermal Stresses - Advanced Theory and Applications|year=2009|publisher=Springer Netherlands|location=Dordrecht|isbn=978-1-4020-9247-3|pages=170|edition=Online-Ausg.}}</ref> {{reference necessary|text=''k''|date=December 2011}}, and ''D'' are also used) is the [[thermal conductivity]] divided by [[density]] and [[specific heat capacity]] at constant pressure.<ref>{{CRC90|page=2-65}}</ref> It measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. It has the [[SI]] unit of m²/s. The formula is:
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| :<math>\alpha = {k \over {\rho c_p}}</math>
| | Feel free to surf to my web site :: web page ([http://saunderstphg.bravejournal.com/entry/142944 look at here]) |
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| where
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| * <math>k</math> is thermal conductivity (W/(m·K))
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| * <math>\rho</math> is density (kg/m³)
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| * <math>c_p</math> is specific heat capacity (J/(kg·K))
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| Together, <math>\rho c_p\,</math> can be considered the [[volumetric heat capacity]] (J/(m³·K)).
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| As seen in the [[heat equation]],
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| :<math>\frac{\partial T}{\partial t} = \alpha \nabla^2 T </math>,
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| thermal diffusivity is the ratio of the [[time derivative]] of [[temperature]] to its [[Second_derivative#Generalization_to_higher_dimensions|curvature]], quantifying the rate at which temperature concavity is "smoothed out". In a sense, thermal diffusivity is the measure of thermal inertia.<ref>{{cite book|last=Venkanna|first=B.K.|title=Fundamentals of Heat and Mass Transfer|url=http://books.google.com/books?id=IIIVHRirRgEC&pg=PA38|accessdate=1 December 2011|year=2010|publisher=PHI Learning|location=New Delhi|isbn=978-81-203-4031-2|page=38}}</ref> In a substance with high thermal diffusivity, heat moves rapidly through it because the substance conducts heat quickly relative to its volumetric heat capacity or 'thermal bulk'.
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| Thermal diffusivity is often measured with the [[Laser flash analysis|flash method]].<ref>[http://www.netzsch.com/en/home/ NETZSCH-Gerätebau, Germany]</ref><ref name="Parker">
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| {{cite journal
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| |author=W.J. Parker, R.J. Jenkins, C.P. Butler, G.L. Abbott
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| |title=Method of Determining Thermal Diffusivity, Heat Capacity and Thermal Conductivity
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| |journal=Journal of Applied Physics
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| |volume=32 |issue=9|page=1679
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| |year=1961
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| |doi= 10.1063/1.1728417
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| |url= http://dx.doi.org/10.1063/1.1728417
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| |bibcode = 1961JAP....32.1679P }}</ref> It involves heating a strip or cylindrical sample with a short energy pulse at one end and analyzing the temperature change (reduction in amplitude and phase shift of the pulse) a short distance away.<ref>
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| {{cite journal
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| |author=J. Blumm, J. Opfermann
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| |title= Improvement of the mathematical modeling of flash measurements
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| |journal=High Temperatures – High Pressures
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| |volume=34 |page=515
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| |year=2002
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| |doi= 10.1068/htjr061
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| |url= http://dx.doi.org/10.1068/htjr061
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| }}</ref><ref>{{cite conference|last=Thermitus|first=M.-A.|editor= Gaal, Daniela S.; Gaal, Peter S. (eds.)|title=New Beam Size Correction for Thermal Diffusivity Measurement with the Flash Method|conference=30th International Thermal Conductivity Conference/18th International Thermal Expansion Symposium|conferenceurl=http://web.archive.org/web/20100128105338/http://www.thermalconductivity.org/|booktitle=Thermal Conductivity 30/Thermal Expansion 18|url=http://books.google.com/books?id=F9row3bxLuYC&pg=PA217|accessdate=1 December 2011|date=October 2010|publisher=DEStech Publications|location=Lancaster, PA|isbn=978-1-60595-015-0|page=217}}</ref>
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| {| class="wikitable sortable"
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| |+Thermal diffusivity of selected materials and substances<ref>{{cite book| title=Introduction to Heat Transfer|edition= 3rd|publisher=McGraw-Hill| year=1958| last1=Brown |last2= Marco}} and {{cite book| last1=Eckert |last2=Drake| title=Heat and Mass Transfer| publisher=McGraw-Hill| year=1959| isbn=0-89116-553-3}} cited in {{cite book| first=J.P. |last=Holman| title=Heat Transfer| edition=9th| publisher=McGraw-Hill|year= 2002| isbn=0-07-029639-1}}</ref>
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| |-
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| ! Material !! class="unsortable" | Thermal diffusivity<br /> (m²/s) !! Thermal diffusivity <br /> (mm²/s)
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| | [[Pyrolytic carbon|Pyrolytic graphite]], parallel to layers || 1.22 × 10<sup>−3</sup> || 1220
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| | Silver, pure (99.9%) || 1.6563 × 10<sup>−4</sup> || 165.63
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| | [[Gold]] || 1.27 × 10<sup>−4</sup> <ref name="eleccool">{{cite journal|url=http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ |title=Materials Data| author= Jim Wilson | date= August 2007 }}</ref> || 127
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| | [[Copper]] at 25°C || 1.11 × 10<sup>−4</sup> <ref name="Casalegno2010">{{cite journal|url= http://www.sciencedirect.com/science/article/pii/S0022311510005337 |title= Measurement of thermal properties of a ceramic/metal joint by laser flash method |volume=407 |issue=2|page=83 | author= V. Casalegno, P. Vavassori, M. Valle, M. Ferraris, M. Salvo, G. Pintsuk| year= 2010 |doi=10.1016/j.jnucmat.2010.09.032|bibcode = 2010JNuM..407...83C }}</ref> || 111
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| | [[Aluminium]] || 8.418 × 10<sup>−5</sup> || 84.18
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| | Al-10Si-Mn-Mg (Silafont 36) at 20°C || 74.2 × 10<sup>−6</sup> <ref>{{cite journal |author= P. Hofer, E. Kaschnitz | title= Thermal diffusivity of the aluminium alloy Al-10Si-Mn-Mg (Silafont 36) in the solid and liquid states |journal= High Temperatures-High Pressures | volume=40 |issue=3-4 |page=311 | year= 2011|url= http://www.oldcitypublishing.com/HTHP/HTHPcontents/HTHP40.3-4contents.html }}</ref> || 74.2
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| | Aluminum 6061-T6 Alloy || 6.4 × 10<sup>−5</sup> <ref name="eleccool"/> || 64
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| | Al-5Mg-2Si-Mn (Magsimal-59) at 20°C || 44.0 × 10<sup>−6</sup> <ref>{{cite journal |author= E. Kaschnitz, M. Küblböck|title=Thermal diffusivity of the aluminium alloy Al-5Mg-2Si-Mn (Magsimal-59) in the solid and liquid states|journal=High Temperatures-High Pressures |volume= 37 |issue=3 |page= 221 | year= 2008 |url= http://www.oldcitypublishing.com/HTHP/HTHPcontents/HTHP37.3contents.html }}</ref> || 44.0
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| | [[Steel]], 1% carbon || 1.172 × 10<sup>−5</sup> || 11.72
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| | Steel, stainless 304A at 27°C || 4.2 × 10<sup>−6</sup> <ref name="eleccool"/> || 4.2
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| | Steel, stainless 310 at 25°C || 3.352 × 10<sup>−6</sup> <ref>{{cite journal |author=J. Blumm, A. Lindemann, B. Niedrig, R. Campbell |title=Measurement of Selected Thermophysical Properties of the NPL Certified Reference Material Stainless Steel 310 |journal=[[International Journal of Thermophysics]] |volume=28 |page=674 |year=2007 |doi= 10.1007/s10765-007-0177-z |url= http://www.springerlink.com/content/4kl8p6717705h766/ |issue=2 |bibcode = 2007IJT....28..674B }}</ref> || 3.352
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| | [[Inconel 600]] at 25°C || 3.428 × 10<sup>−6</sup> <ref>{{cite journal |author= J. Blumm , A. Lindemann, B. Niedrig |title= Measurement of the thermophysical properties of an NPL thermal conductivity standard Inconel 600|journal= High Temperatures-High Pressures |volume=35/36 |issue=6 |page=621 | year= 2003/2007 |url=http://www.perceptionweb.com/abstract.cgi?id=htjr145 }}</ref> || 3.428
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| | [[Molybdenum]] (99.95%) at 25°C || 54.3 × 10<sup>−6</sup> <ref>{{cite conference|conference=17th [[PLANSEE|Plansee]] Seminar |title= Measurement of the Thermophysical Properties of Pure Molybdenum | author= A. Lindemann, J. Blumm | year= 2009 |volume=3 }}</ref> || 54.3
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| | Iron || 2.3 × 10<sup>−5</sup> <ref name="eleccool"/> || 23
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| | Silicon || 8.8 × 10<sup>−5</sup> <ref name="eleccool"/> || 88
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| | Quartz || 1.4 × 10<sup>−6</sup> <ref name="eleccool"/> || 1.4
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| | Carbon/carbon composite at 25°C || 216.5 × 10<sup>−6</sup> <ref name=" Casalegno2010" /> || 216.5
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| | Aluminium oxide (polycrystalline) || 1.20 × 10<sup>−5</sup> || 12.0
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| | Silicon Dioxide (Polycrystalline) || 8.3 × 10<sup>−7</sup> <ref name="eleccool"/> || 0.83
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| | Si<sub>3</sub> N<sub>4</sub> with [[carbon nanotube|CNTs]] 26°C || 9.142 × 10<sup>−6</sup> <ref name="Koszor2009">{{cite journal |journal=Key Engineering Materials|url= http://www.scientific.net/KEM.409.354 |title= Observation of thermophysical and tribological properties of CNT reinforced Si<sub>3</sub> N<sub>4</sub> |volume=409 |page=354 | author= O. Koszor, A. Lindemann, F. Davin, C. Balázsi| year= 2009 |doi= 10.4028/www.scientific.net/KEM.409.354 }}</ref> || 9.142
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| | Si<sub>3</sub> N<sub>4</sub> without [[carbon nanotube|CNTs]] 26°C || 8.605 × 10<sup>−6</sup> <ref name=" Koszor2009" /> || 8.605
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| | [[Polycarbonate|PC]] (Polycarbonate) at 25°C || 0.144 × 10<sup>−6</sup> <ref name="HTHP3536pp627">{{cite journal |author= J. Blumm, A. Lindemann |title= Characterization of the thermophysical properties of molten polymers and liquids using the flash technique |journal=High Temperatures-High Pressures |volume= 35/36 |issue=6 |page= 627 | year= 2003/2007 |doi= 10.1068/htjr144 }}</ref> || 0.144
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| | [[polypropylene|PP]] (Polypropylene) at 25°C || 0.096 × 10<sup>−6</sup> <ref name="HTHP3536pp627"/> || 0.096
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| | Paraffin at 25°C || 0.081 × 10<sup>−6</sup> <ref name="HTHP3536pp627"/> || 0.081
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| | [[PVC]] (Polyvinyl Chloride) || 8 × 10<sup>−8</sup> <ref name="eleccool"/> || 0.08
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| | [[PTFE]] (Polytetrafluorethylene) at 25°C|| 0.124 × 10<sup>−6</sup> <ref>{{cite journal |author= J. Blumm, A. Lindemann, M. Meyer, C. Strasser | title= Characterization of PTFE Using Advanced Thermal Analysis Technique |journal= International Journal of Thermophysics| volume=40 |issue=3-4 |page=311 | year= 2011|doi= 10.1007/s10765-008-0512-z |bibcode = 2010IJT....31.1919B }}</ref> || 0.124
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| | Water at 25°C || 0.143 × 10<sup>−6</sup> <ref name="HTHP3536pp627"/> || 0.143
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| | Alcohol || 7 × 10<sup>−8</sup> <ref name="eleccool"/> || 0.07
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| | Water vapour (1 atm, 400 K) || 2.338 × 10<sup>−5</sup> || 23.38
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| | Air (300 K) || 1.9 × 10<sup>−5</sup> <ref name="eleccool"/> || 19
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| | Argon (300 K, 1 atm) || {{val|2.2|e=-5}}<ref name="baierlein">{{cite book|editor-last=Lide|editor-first=David R.|title=CDC Handbook of Chemistry and Physics|edition=71st|year=1992|publisher=Chemical Rubber Publishing Company|location=Boston}} cited in {{cite book|last=Baierlein|first=Ralph|title=Thermal Physics|url=http://books.google.com/books?id=fqUU71spbZYC&pg=PA372|accessdate=1 December 2011|year=1999|publisher=Cambridge University Press|location=Cambridge, UK|isbn=0-521-59082-5|page=372}}</ref> || 22
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| | Helium (300 K, 1 atm) || {{val|1.9|e=-4}}<ref name="baierlein"/> || 190
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| | Hydrogen (300 K, 1 atm) || {{val|1.6|e=-4}}<ref name="baierlein"/> || 160
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| | Nitrogen (300 K, 1 atm) || {{val|2.2|e=-5}}<ref name="baierlein"/> || 22
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| | Pyrolytic graphite, normal to layers || 3.6 × 10<sup>−6</sup> || 3.6
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| | Sandstone || 1.12–1.19 × 10<sup>−6</sup> || 1.15
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| | Tin || 4.0 × 10<sup>−5</sup> <ref name="eleccool"/> || 40
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| | Brick, common || 5.2 × 10<sup>−7</sup> || 0.52
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| | Brick, adobe || 2.7 × 10<sup>−7</sup> || 0.27
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| | Glass, window || 3.4 × 10<sup>−7</sup> || 0.34
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| | Rubber || 1.3 × 10<sup>−7</sup>{{Citation needed|date=December 2011}}<!--individually added by IP user--> || 0.13
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| | Nylon || 9 × 10<sup>−8</sup> || 0.09
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| | Wood (Yellow Pine) || 8.2 × 10<sup>−8</sup> || 0.082
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| | Oil, engine (saturated liquid, 100 °C) || 7.38 × 10<sup>−8</sup> || 0.0738
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| |}
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| ==See also==
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| * [[Heat equation]]
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| * [[Laser Flash Analysis|Laser flash analysis]]
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| * [[Thermodiffusion]]
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| * [[Thermal effusivity]]
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| * [[Thermal time constant]]
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| ==References==
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| {{Reflist}}
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| | |
| {{DEFAULTSORT:Thermal Diffusivity}}
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| [[Category:Heat transfer]]
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| [[Category:Physical quantities]]
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| [[Category:Heat conduction]]
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