Thermal diffusivity
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In heat transfer analysis, thermal diffusivity (usually denoted α but a, κ, k[citation needed], and D are also used) is the thermal conductivity divided by density and specific heat capacity at constant pressure.[1] It has the SI unit of m²/s. The formula is:
where
- k is thermal conductivity (W/(m·K))
- ρ is density (kg/m³)
- cp is specific heat capacity (J/(kg·K))
The denominator 
can be considered the volumetric heat capacity (J/(m³·K)).
In a sense, thermal diffusivity is the measure of thermal inertia.[2] In a substance with high thermal diffusivity, heat moves rapidly through because the substance conducts heat quickly relative to its volumetric heat capacity or 'thermal bulk'. The substance generally does not require much energy transfer to or from its surroundings to reach thermal equilibrium.[citation needed]
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.[3]
| Material | Thermal diffusivity (m²/s) |
Thermal diffusivity (mm²/s) |
|---|---|---|
| Pyrolytic graphite, parallel to layers | 1.22 × 10−3 | 1220 |
| Silver, pure (99.9%) | 1.6563 × 10−4 | 165.63 |
| Gold | 1.27 × 10−4 [5] | 127 |
| Copper | 1.1234 × 10−4 | 112.34 |
| Aluminium | 8.418 × 10−5 | 84.18 |
| Al-10Si-Mn-Mg (Silafont 36) at 20°C | 74.2 × 10−6 [6] | 74.2 |
| Aluminum 6061-T6 Alloy | 6.4 × 10−5 [5] | 64 |
| Al-5Mg-2Si-Mn (Magsimal-59) at 20°C | 44.0 × 10−6 [7] | 44.0 |
| Steel, 1% carbon | 1.172 × 10−5 | 11.72 |
| Steel, stainless 304A | 4.2 × 10−6 [5] | 4.2 |
| Inconel 600 at 25°C | 3.428 × 10−6 [8] | 3.428 |
| Iron | 2.3 × 10−5 [5] | 23 |
| Silicon | 8.8 × 10−5 [5] | 88 |
| Quartz | 1.4 × 10−6 [5] | 1.4 |
| Aluminium oxide (polycrystalline) | 1.20 × 10−5 | 12.0 |
| Silicon Dioxide (Polycrystalline) | 8.3 × 10−7 [5] | 0.83 |
| PC (Polycarbonate) at 25°C | 0.144 × 10−6 [9] | 0.144 |
| PP (Polypropylene) at 25°C | 0.096 × 10−6 [9] | 0.096 |
| Paraffin at 25°C | 0.081 × 10−6 [9] | 0.081 |
| PVC (Polyvinyl Chloride) | 8 × 10−8 [5] | 0.08 |
| PTFE (Polytetrafluorethylene) at 25°C | 0.124 × 10−6 [10] | 0.124 |
| Water at 25°C | 0.143 × 10−6 [9] | 0.143 |
| Alcohol | 7 × 10−8 [5] | 0.07 |
| Water vapour (1 atm, 400 K) | 2.338 × 10−5 | 23.38 |
| Air | 1.9 × 10−5 [5] | 19 |
| Argon (300 K, 1 atm) | 2.2×10−5[11] | 22 |
| Helium (300 K, 1 atm) | 1.9×10−4[11] | 190 |
| Hydrogen (300 K, 1 atm) | 1.6×10−4[11] | 160 |
| Nitrogen (300 K, 1 atm) | 2.2×10−5[11] | 22 |
| Pyrolytic graphite, normal to layers | 3.6 × 10−6 | 3.6 |
| Sandstone | 1.12–1.19 × 10−6 | 1.15 |
| Tin | 4.0 × 10−5 [5] | 40 |
| Brick, common | 5.2 × 10−7 | 0.52 |
| Glass, window | 3.4 × 10−7 | 0.34 |
| Rubber | 1.3 × 10−7[citation needed] | 0.13 |
| Nylon | 9 × 10−8 | 0.09 |
| Wood (Yellow Pine) | 8.2 × 10−8 | 0.082 |
| Oil, engine (saturated liquid, 100 °C) | 7.38 × 10−8 | 0.0738 |
[edit] See also
[edit] References
- ^ Lide, David R. (2009). Handbook of Chemistry and Physics (90 ed.). Boca Raton, Florida: CRC Press. p. 2-65. ISBN 978-1-4200-9084-0.
- ^ Venkanna, B.K. (2010). Fundamentals of Heat and Mass Transfer. New Delhi: PHI Learning. p. 38. ISBN 978-81-203-4031-2. http://books.google.com/books?id=IIIVHRirRgEC&pg=PA38. Retrieved 1 December 2011.
- ^ 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. http://books.google.com/books?id=F9row3bxLuYC&pg=PA217. Retrieved 1 December 2011.
- ^ Brown; Marco (1958). Introduction to Heat Transfer (3rd ed.). McGraw-Hill. and Eckert; Drake (1959). Heat and Mass Transfer. McGraw-Hill. ISBN 0891165533. cited in Holman, J.P. (2002). Heat Transfer (9th ed.). McGraw-Hill. ISBN 0070296391.
- ^ a b c d e f g h i j k Jim Wilson (August 2007). Materials Data. http://www.electronics-cooling.com/2007/08/thermal-diffusivity/.
- ^ 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.
- ^ 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.
- ^ 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. http://www.perceptionweb.com/abstract.cgi?id=htjr145.
- ^ a b c d J. Blumm, A. Lindemann (2003/2007). "Characterization of the thermophysical properties of molten polymers and liquids using the flash technique". High Temperatures-High Pressures 35/36 (6): 627. doi:10.1068/htjr144.
- ^ 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. doi:10.1007/s10765-008-0512-z.
- ^ a b c d 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 0-521-59082-5. http://books.google.com/books?id=fqUU71spbZYC&pg=PA372. Retrieved 1 December 2011.
