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Rate at which heat spreads throughout a material From Wikipedia, the free encyclopedia
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] ,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]
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] |