Thermal diffusivity

Source: Wikipedia, the free encyclopedia.

In

thermal conductivity divided by density and specific heat capacity at constant pressure.[1] It is a measure of the rate of heat transfer inside a material. It has units of m2/s. Thermal diffusivity is usually denoted by lowercase alpha (α), but a, h, κ (kappa),[2] K,[3]
and D are also used.

The formula is:[4]

where

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

As seen in the heat equation,[5]

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". Thermal diffusivity is a contrasting measure to thermal effusivity.[6][7] 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 flash method.[8][9] 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.[10][11]

Thermal diffusivity of selected materials and substances

Thermal diffusivity of selected materials and substances[12]
Material Thermal diffusivity (mm2/s) References
Pyrolytic graphite, parallel to layers 1,220
Diamond 1,060 - 1,160
Carbon/carbon composite at 25 °C 216.5 [13]
Helium (300 K, 1 atm) 190 [14]
Silver, pure (99.9%) 165.63
Hydrogen (300 K, 1 atm) 160 [14]
Gold 127 [15]
Copper at 25 °C 111 [13]
Aluminium 97 [15]
Silicon 88 [15]
Al-10Si-Mn-Mg (Silafont 36) at 20 °C 74.2 [16]
Aluminium 6061-T6 Alloy 64 [15]
Molybdenum (99.95%) at 25 °C 54.3 [17]
Al-5Mg-2Si-Mn (Magsimal-59) at 20 °C 44.0 [18]
Tin 40 [15]
Water vapor (1 atm, 400 K) 23.38
Iron 23 [15]
Argon (300 K, 1 atm) 22 [14]
Nitrogen (300 K, 1 atm) 22 [14]
Air (300 K) 19 [15]
Steel, AISI 1010 (0.1% carbon) 18.8 [19]
Aluminium oxide (polycrystalline) 12.0
Steel, 1% carbon 11.72
Si3N4 with CNTs 26 °C 9.142 [20]
Si3N4 without CNTs 26 °C 8.605 [20]
Steel, stainless 304A at 27 °C 4.2 [15]
Pyrolytic graphite, normal to layers 3.6
Steel, stainless 310 at 25 °C 3.352 [21]
Inconel 600
at 25 °C		 3.428 [22]
Quartz 1.4 [15]
Sandstone 1.15
Ice at 0 °C 1.02
Silicon dioxide (polycrystalline) 0.83 [15]
Brick, common 0.52
Glass, window 0.34
Brick, adobe 0.27
PC (polycarbonate) at 25 °C 0.144 [23]
Water at 25 °C 0.143 [23]
PTFE
(Polytetrafluorethylene) at 25 °C 		0.124 [24]
PP (polypropylene) at 25 °C 0.096 [23]
Nylon 0.09
Rubber 0.089 - 0.13 [3]
Wood (yellow pine) 0.082
Paraffin at 25 °C 0.081 [23]
PVC
(polyvinyl chloride)		 0.08 [15]
Oil, engine (saturated liquid, 100 °C) 0.0738
Alcohol 0.07 [15]

See also

References

  1. ISBN 978-1-4200-9084-0
    .
  2. ISBN 978-1-4020-9247-3
    .
  3. ^
    doi:10.1119/1.11601
  4. ISBN 978-0-471-07392-5.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  5. ISBN 978-0-19-853368-9
  6. doi:10.1016/B978-0-08-100619-1.00009-2
    .
  7. ISBN 978-81-203-4031-2
    . Retrieved 1 December 2011.
  8. ^ "NETZSCH-Gerätebau, Germany". Archived from the original on 2012-03-11. Retrieved 2012-03-12.
  9. ^ W.J. Parker; R.J. Jenkins; C.P. Butler; G.L. Abbott (1961). "Method of Determining Thermal Diffusivity, Heat Capacity and Thermal Conductivity". Journal of Applied Physics. 32 (9): 1679.
    doi:10.1063/1.1728417
    .
  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
    .
  11. ISBN 978-1-60595-015-0
    . Retrieved 1 December 2011.
  12. ISBN 978-0-07-029639-8
    .
  13. ^
    doi:10.1016/j.jnucmat.2010.09.032
    .
  14. ^
    ISBN 978-0-521-59082-2
    . Retrieved 1 December 2011.
  15. ^ a b c d e f g h i j k l Jim Wilson (August 2007). "Materials Data". {{cite journal}}: Cite journal requires |journal= (help)
  16. ^ 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.
  17. Plansee
    Seminar. Vol. 3.
  18. ^ 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.
  19. ^ 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)
  20. ^
    S2CID 136957396
    .
  21. S2CID 120628607
    .
  22. doi:10.1068/htjr145
    .
  23. ^
    doi:10.1068/htjr144
    .
  24. S2CID 122020437
    .
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