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In [[heat transfer]] analysis, '''thermal diffusivity''' (usually denoted ''&alpha;'' but ''a'', ''&kappa;'',<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>
 
where
* <math>k</math> is thermal conductivity (W/(m·K))
* <math>\rho</math> is density (kg/m³)
* <math>c_p</math> is specific heat capacity (J/(kg·K))
 
Together, <math>\rho c_p\,</math> can be considered the [[volumetric heat capacity]] (J/(m³·K)).
 
As seen in the [[heat equation]],
 
:<math>\frac{\partial T}{\partial t} = \alpha \nabla^2 T </math>,
 
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'.
 
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">
{{cite journal
|author=W.J. Parker, R.J. Jenkins, C.P. Butler, G.L. Abbott
|title=Method of Determining Thermal Diffusivity, Heat Capacity and Thermal Conductivity
|journal=Journal of Applied Physics
|volume=32  |issue=9|page=1679
|year=1961
|doi= 10.1063/1.1728417
|url= http://dx.doi.org/10.1063/1.1728417
|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>
{{cite journal
|author=J. Blumm, J. Opfermann
|title= Improvement of the mathematical modeling of flash measurements
|journal=High Temperatures – High Pressures
|volume=34  |page=515
|year=2002
|doi= 10.1068/htjr061
|url= http://dx.doi.org/10.1068/htjr061
}}</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>
 
{| class="wikitable sortable"
|+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>
|-
! Material !! class="unsortable" | Thermal diffusivity<br /> (m²/s) !! Thermal diffusivity <br /> (mm²/s)
|-
| [[Pyrolytic carbon|Pyrolytic graphite]], parallel to layers || 1.22 × 10<sup>−3</sup> || 1220
|-
| Silver, pure (99.9%) || 1.6563 × 10<sup>−4</sup> || 165.63
|-
| [[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
|-
| [[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
|-
| [[Aluminium]] || 8.418 × 10<sup>−5</sup> || 84.18
|-
| 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
|-
| Aluminum 6061-T6  Alloy || 6.4  × 10<sup>−5</sup>  <ref name="eleccool"/> || 64
|-
| 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
|-
| [[Steel]], 1% carbon || 1.172 × 10<sup>−5</sup> || 11.72
|-
| Steel, stainless 304A at 27°C  || 4.2 × 10<sup>−6</sup> <ref name="eleccool"/> || 4.2
|-
| 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
|-
| [[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
|-
| [[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
|-
| Iron ||  2.3 × 10<sup>−5</sup> <ref name="eleccool"/> || 23
|-
| Silicon  || 8.8 × 10<sup>−5</sup> <ref name="eleccool"/> || 88
|-
| Quartz || 1.4 × 10<sup>−6</sup> <ref name="eleccool"/> || 1.4
|-
| Carbon/carbon  composite at 25°C  || 216.5 × 10<sup>−6</sup> <ref  name=" Casalegno2010" /> || 216.5
|-
| Aluminium oxide (polycrystalline) || 1.20 × 10<sup>−5</sup> || 12.0
|-
| Silicon Dioxide (Polycrystalline)  || 8.3 × 10<sup>−7</sup> <ref name="eleccool"/> || 0.83
|-
|  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
|-
| 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
|-
| [[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
|-
| [[polypropylene|PP]] (Polypropylene) at 25°C  || 0.096 × 10<sup>−6</sup> <ref  name="HTHP3536pp627"/> || 0.096
|-
| Paraffin at 25°C  || 0.081 × 10<sup>−6</sup> <ref  name="HTHP3536pp627"/> || 0.081
|-
| [[PVC]] (Polyvinyl Chloride)  || 8 × 10<sup>−8</sup> <ref name="eleccool"/> || 0.08
|-
| [[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
|-       
| Water at 25°C  || 0.143 × 10<sup>−6</sup> <ref  name="HTHP3536pp627"/> || 0.143
|-
| Alcohol || 7 × 10<sup>−8</sup> <ref name="eleccool"/> || 0.07
|-
| Water vapour (1 atm, 400 K) || 2.338 × 10<sup>−5</sup> || 23.38
|-
| Air (300 K) || 1.9 × 10<sup>−5</sup> <ref name="eleccool"/> || 19
|-
| 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
|-
| Helium (300 K, 1 atm) || {{val|1.9|e=-4}}<ref name="baierlein"/> || 190
|-
| Hydrogen (300 K, 1 atm) || {{val|1.6|e=-4}}<ref name="baierlein"/> || 160
|-
| Nitrogen (300 K, 1 atm) || {{val|2.2|e=-5}}<ref name="baierlein"/> || 22
|-
| Pyrolytic graphite, normal to layers || 3.6 × 10<sup>−6</sup> || 3.6
|-
| Sandstone || 1.12–1.19 × 10<sup>−6</sup> || 1.15
|-
| Tin || 4.0 × 10<sup>−5</sup>  <ref name="eleccool"/>  || 40
|-
| Brick, common || 5.2 × 10<sup>−7</sup> || 0.52
|-
| Brick, adobe || 2.7 × 10<sup>−7</sup> || 0.27
|-
| Glass, window || 3.4 × 10<sup>−7</sup> || 0.34
|-
| Rubber || 1.3 × 10<sup>−7</sup>{{Citation needed|date=December 2011}}<!--individually added by IP user--> || 0.13
|-
| Nylon || 9 × 10<sup>−8</sup> || 0.09
|-
| Wood (Yellow Pine) || 8.2 × 10<sup>−8</sup> || 0.082
|-
| Oil, engine (saturated liquid, 100 °C) || 7.38 × 10<sup>−8</sup> || 0.0738
|}
 
==See also==
* [[Heat equation]]
* [[Laser Flash Analysis|Laser flash analysis]]
* [[Thermodiffusion]]
* [[Thermal effusivity]]
* [[Thermal time constant]]
 
==References==
{{Reflist}}
 
{{DEFAULTSORT:Thermal Diffusivity}}
[[Category:Heat transfer]]
[[Category:Physical quantities]]
[[Category:Heat conduction]]

Revision as of 02:38, 26 February 2014

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In order to remove the programs on the computer, Windows Installer should be in a healthy state. If its installation is corrupted we could receive error 1721 in Windows 7, Vista and XP during the system removal process. Simply re-registering its component files would resolve your issue.

The registry cleaner could come because standard with a back up and restore center. This ought to be an simple to implement procedure.That signifies which if you encounter a issue with the PC following utilizing a registry cleaning we can just restore the settings.

Windows relies heavily on this database, storing everything from the newest emails to your Internet favorites inside there. Because it's thus crucial, a computer is regularly adding plus updating the files inside it. This is okay, nevertheless it will make your computer run slow, when the computer accidentally breaks its crucial registry files. This is a quite widespread issue, plus actually makes the computer run slower each day. What occurs is the fact that because your computer is consistently utilizing 100's of registry files at when, it sometimes gets confused plus make certain of them unreadable. This then makes a computer run slow, because Windows takes longer to read the files it demands.

You want a choice to automatically delete unwelcome registry keys. This usually conserve you hours of laborious checking by your registry keys. Automatic deletion is a key element when we compare registry cleaners.

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