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Thermal diffusivity
Physical quantity that measures the rate of transfer of heat of a material from the hot side to the cold side

In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI units of m2/s. It is an intensive property. Thermal diffusivity is usually denoted by lowercase alpha (α), but a, h, κ (kappa), K, D, D T {\displaystyle D_{T}} are also used.

The formula is α = k ρ c p , {\displaystyle \alpha ={\frac {k}{\rho c_{p}}},} where

k is thermal conductivity (W/(m·K)), cp is specific heat capacity (J/(kg·K)), ρ is density (kg/m3).

Together, ρcp can be considered the volumetric heat capacity (J/(m3·K)).

Thermal diffusivity is a positive coefficient in the heat equation: ∂ T ∂ t = α ∇ 2 T . {\displaystyle {\frac {\partial T}{\partial t}}=\alpha \nabla ^{2}T.}

One way to view thermal diffusivity is as the ratio of the time derivative of temperature to its curvature, quantifying the rate at which temperature concavity is "smoothed out". In a substance with high thermal diffusivity, heat moves rapidly through it because the substance conducts heat quickly relative to its energy storage capacity or "thermal bulk".

Thermal diffusivity and thermal effusivity are related concepts and quantities used to simulate non-equilibrium thermodynamics. Diffusivity is the more fundamental concept and describes the stochastic process of heat spread throughout some local volume of a substance. Effusivity describes the corresponding transient process of heat flow through some local area of interest. Upon reaching a steady state, where the stored energy distribution stabilizes, the thermal conductivity (k) may be sufficient to describe heat transfers inside solid or rigid bodies by applying Fourier's law.

Thermal diffusivity is often measured with the flash method. 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.

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Thermal diffusivity of selected materials and substances

Thermal diffusivity of selected materials and substances12
MaterialThermal diffusivity(mm2/s)Refs.
Pyrolytic graphite, parallel to layers1,220
Diamond1,060–1,160
Carbon/carbon composite at 25 °C216.513
Helium (300 K, 1 atm)19014
Silver, pure (99.9%)165.63
Hydrogen (300 K, 1 atm)16015
Gold12716
Copper at 25 °C11117
Aluminium9718
Silicon8819
Al-10Si-Mn-Mg (Silafont 36) at 20 °C74.220
Aluminium 6061-T6 Alloy6421
Molybdenum (99.95%) at 25 °C54.322
Al-5Mg-2Si-Mn (Magsimal-59) at 20 °C44.023
Tin4024
Water vapor (1 atm, 400 K)23.38
Iron2325
Argon (300 K, 1 atm)2226
Nitrogen (300 K, 1 atm)2227
Air (300 K)1928
Steel, AISI 1010 (0.1% carbon)18.829
Aluminium oxide (polycrystalline)12.0
Steel, 1% carbon11.72
Si3N4 with CNTs 26 °C9.14230
Si3N4 without CNTs 26 °C8.60531
Steel, stainless 304A at 27 °C4.232
Pyrolytic graphite, normal to layers3.6
Steel, stainless 310 at 25 °C3.35233
Inconel 600 at 25 °C3.42834
Quartz1.435
Sandstone1.15
Ice at 0 °C1.02
Silicon dioxide (polycrystalline)0.8336
Brick, common0.52
Glass, window0.34
Brick, adobe0.27
PC (polycarbonate) at 25 °C0.14437
Water at 25 °C0.14338
PTFE (Polytetrafluorethylene) at 25 °C0.12439
PP (polypropylene) at 25 °C0.09640
Nylon0.09
Rubber0.089–0.1341
Wood (yellow pine)0.082
Paraffin at 25 °C0.08142
PVC (polyvinyl chloride)0.0843
Oil, engine (saturated liquid, 100 °C)0.0738
Alcohol0.0744

See also

References

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  3. Unsworth, J.; Duarte, From. J. (1979). "Heat diffusion in a solid sphere and Fourier Theory". Am. J. Phys. 47 (11): 891–893. Bibcode:1979AmJPh..47..981U. doi:10.1119/1.11601. /wiki/F._J._Duarte ↩

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  10. J. Blumm; J. Opfermann (2002). "Improvement of the mathematical modeling of flash measurements". High Temperatures – High Pressures. 34 (5): 515. doi:10.1068/htjr061. /wiki/Doi_(identifier) ↩

  11. Thermitus, M.-A. (October 2010). "New Beam Size Correction for Thermal Diffusivity Measurement with the Flash Method". In Gaal, Daniela S.; Gaal, Peter S. (eds.). Thermal Conductivity 30/Thermal Expansion 18. 30th International Thermal Conductivity Conference/18th International Thermal Expansion Symposium. Lancaster, PA: DEStech Publications. p. 217. ISBN 978-1-60595-015-0. Retrieved 1 December 2011. 978-1-60595-015-0 ↩

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  13. V. Casalegno; P. Vavassori; M. Valle; M. Ferraris; M. Salvo; G. Pintsuk (2010). "Measurement of thermal properties of a ceramic/metal joint by laser flash method". Journal of Nuclear Materials. 407 (2): 83. Bibcode:2010JNuM..407...83C. doi:10.1016/j.jnucmat.2010.09.032. /wiki/Bibcode_(identifier) ↩

  14. Lide, David R., ed. (1992). CDC Handbook of Chemistry and Physics (71st ed.). Boston: Chemical Rubber Publishing Company. cited in Baierlein, Ralph (1999). Thermal Physics. Cambridge, UK: Cambridge University Press. p. 372. ISBN 978-0-521-59082-2. Retrieved 1 December 2011. 978-0-521-59082-2 ↩

  15. Lide, David R., ed. (1992). CDC Handbook of Chemistry and Physics (71st ed.). Boston: Chemical Rubber Publishing Company. cited in Baierlein, Ralph (1999). Thermal Physics. Cambridge, UK: Cambridge University Press. p. 372. ISBN 978-0-521-59082-2. Retrieved 1 December 2011. 978-0-521-59082-2 ↩

  16. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  17. V. Casalegno; P. Vavassori; M. Valle; M. Ferraris; M. Salvo; G. Pintsuk (2010). "Measurement of thermal properties of a ceramic/metal joint by laser flash method". Journal of Nuclear Materials. 407 (2): 83. Bibcode:2010JNuM..407...83C. doi:10.1016/j.jnucmat.2010.09.032. /wiki/Bibcode_(identifier) ↩

  18. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  19. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  20. P. Hofer; E. Kaschnitz (2011). "Thermal diffusivity of the aluminium alloy Al-10Si-Mn-Mg (Silafont 36) in the solid and liquid states". High Temperatures – High Pressures. 40 (3–4): 311. http://www.oldcitypublishing.com/HTHP/HTHPcontents/HTHP40.3-4contents.html ↩

  21. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  22. A. Lindemann; J. Blumm (2009). Measurement of the Thermophysical Properties of Pure Molybdenum. 17th Plansee Seminar. Vol. 3. /wiki/PLANSEE ↩

  23. E. Kaschnitz; M. Küblböck (2008). "Thermal diffusivity of the aluminium alloy Al-5Mg-2Si-Mn (Magsimal-59) in the solid and liquid states". High Temperatures – High Pressures. 37 (3): 221. http://www.oldcitypublishing.com/HTHP/HTHPcontents/HTHP37.3contents.html ↩

  24. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  25. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  26. Lide, David R., ed. (1992). CDC Handbook of Chemistry and Physics (71st ed.). Boston: Chemical Rubber Publishing Company. cited in Baierlein, Ralph (1999). Thermal Physics. Cambridge, UK: Cambridge University Press. p. 372. ISBN 978-0-521-59082-2. Retrieved 1 December 2011. 978-0-521-59082-2 ↩

  27. Lide, David R., ed. (1992). CDC Handbook of Chemistry and Physics (71st ed.). Boston: Chemical Rubber Publishing Company. cited in Baierlein, Ralph (1999). Thermal Physics. Cambridge, UK: Cambridge University Press. p. 372. ISBN 978-0-521-59082-2. Retrieved 1 December 2011. 978-0-521-59082-2 ↩

  28. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  29. Lienhard, John H. Lienhard, John H. (2019). A Heat Transfer Textbook (5th ed.). Dover Pub. p. 715.{{cite book}}: CS1 maint: multiple names: authors list (link) /wiki/Template:Cite_book ↩

  30. O. Koszor; A. Lindemann; F. Davin; C. Balázsi (2009). "Observation of thermophysical and tribological properties of CNT reinforced Si3 N4". Key Engineering Materials. 409: 354. doi:10.4028/www.scientific.net/KEM.409.354. S2CID 136957396. /wiki/Doi_(identifier) ↩

  31. O. Koszor; A. Lindemann; F. Davin; C. Balázsi (2009). "Observation of thermophysical and tribological properties of CNT reinforced Si3 N4". Key Engineering Materials. 409: 354. doi:10.4028/www.scientific.net/KEM.409.354. S2CID 136957396. /wiki/Doi_(identifier) ↩

  32. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  33. J. Blumm; A. Lindemann; B. Niedrig; R. Campbell (2007). "Measurement of Selected Thermophysical Properties of the NPL Certified Reference Material Stainless Steel 310". International Journal of Thermophysics. 28 (2): 674. Bibcode:2007IJT....28..674B. doi:10.1007/s10765-007-0177-z. S2CID 120628607. /wiki/International_Journal_of_Thermophysics ↩

  34. J. Blumm; A. Lindemann; B. Niedrig (2003–2007). "Measurement of the thermophysical properties of an NPL thermal conductivity standard Inconel 600". High Temperatures – High Pressures. 35/36 (6): 621. doi:10.1068/htjr145. http://www.perceptionweb.com/abstract.cgi?id=htjr145 ↩

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  36. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  37. J. Blumm; A. Lindemann (2003–2007). "Characterization of the thermophysical properties of molten polymers and liquids using the flash technique" (PDF). High Temperatures – High Pressures. 35/36 (6): 627. doi:10.1068/htjr144. http://www.eyoungindustry.com/uploadfile/file/20151027/20151027211034_96662.pdf ↩

  38. J. Blumm; A. Lindemann (2003–2007). "Characterization of the thermophysical properties of molten polymers and liquids using the flash technique" (PDF). High Temperatures – High Pressures. 35/36 (6): 627. doi:10.1068/htjr144. http://www.eyoungindustry.com/uploadfile/file/20151027/20151027211034_96662.pdf ↩

  39. J. Blumm; A. Lindemann; M. Meyer; C. Strasser (2011). "Characterization of PTFE Using Advanced Thermal Analysis Technique". International Journal of Thermophysics. 40 (3–4): 311. Bibcode:2010IJT....31.1919B. doi:10.1007/s10765-008-0512-z. S2CID 122020437. /wiki/Bibcode_(identifier) ↩

  40. J. Blumm; A. Lindemann (2003–2007). "Characterization of the thermophysical properties of molten polymers and liquids using the flash technique" (PDF). High Temperatures – High Pressures. 35/36 (6): 627. doi:10.1068/htjr144. http://www.eyoungindustry.com/uploadfile/file/20151027/20151027211034_96662.pdf ↩

  41. Unsworth, J.; Duarte, From. J. (1979). "Heat diffusion in a solid sphere and Fourier Theory". Am. J. Phys. 47 (11): 891–893. Bibcode:1979AmJPh..47..981U. doi:10.1119/1.11601. /wiki/F._J._Duarte ↩

  42. J. Blumm; A. Lindemann (2003–2007). "Characterization of the thermophysical properties of molten polymers and liquids using the flash technique" (PDF). High Temperatures – High Pressures. 35/36 (6): 627. doi:10.1068/htjr144. http://www.eyoungindustry.com/uploadfile/file/20151027/20151027211034_96662.pdf ↩

  43. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩

  44. Jim Wilson (August 2007). "Materials Data". Electronics Cooling. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/ ↩