Thermal diffusivity

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In heat transfer analysis, thermal diffusivity is the 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 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), [2] K, [3] ,D, are also used.

Contents

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]
MaterialThermal diffusivity (mm2/s)References
Pyrolytic graphite, parallel to layers1,220
Diamond 1,060 - 1,160
Carbon/carbon composite at 25 °C216.5 [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 °C111 [13]
Aluminium 97 [15]
Silicon88 [15]
Al-10Si-Mn-Mg (Silafont 36) at 20 °C74.2 [16]
Aluminium 6061-T6 Alloy64 [15]
Molybdenum (99.95%) at 25 °C54.3 [17]
Al-5Mg-2Si-Mn (Magsimal-59) at 20 °C44.0 [18]
Tin40 [15]
Water vapor (1 atm, 400 K)23.38
Iron23 [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% carbon11.72
Si3N4 with CNTs 26 °C9.142 [20]
Si3N4 without CNTs 26 °C8.605 [20]
Steel, stainless 304A at 27 °C4.2 [15]
Pyrolytic graphite, normal to layers3.6
Steel, stainless 310 at 25 °C3.352 [21]
Inconel 600 at 25 °C3.428 [22]
Quartz1.4 [15]
Sandstone1.15
Ice at 0 °C1.02
Silicon dioxide (polycrystalline)0.83 [15]
Brick, common0.52
Glass, window0.34
Brick, adobe0.27
PC (polycarbonate) at 25 °C0.144 [23]
Water at 25 °C0.143 [23]
PTFE (Polytetrafluorethylene) at 25 °C0.124 [24]
PP (polypropylene) at 25 °C0.096 [23]
Nylon0.09
Rubber0.089 - 0.13 [3]
Wood (yellow pine)0.082
Paraffin at 25 °C0.081 [23]
PVC (polyvinyl chloride)0.08 [15]
Oil, engine (saturated liquid, 100 °C)0.0738
Alcohol0.07 [15]

See also

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References

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