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. 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]
Together, ρcp can be considered the volumetric heat capacity (J/(m3·K)).
As seen in the heat equation,[5]
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]
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] |
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