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Thermal diffusivity

In heat transfer analysis, thermal diffusivity (symbol: \kappa\,, but note that the symbols α, D, and k are all commonly used) is the ratio of thermal conductivity to volumetric heat capacity.

\kappa = {k \over {\rho c_p}}

where: k\, is thermal conductivity (SI units: watts per metre-kelvin, W∙m-1∙K-1) \rho c_p\, is the volumetric heat capacity (density kg∙m-3 times specific heat capacity J∙kg-1K-1; SI units: joules per cubic metre-kelvin, J∙m-3∙K-1)

The SI units for thermal diffusivity are square metres per second or m2∙s-1.

Substances with high thermal diffusivity rapidly adjust their temperature to that of their surroundings, because they conduct heat quickly in comparison to their thermal 'bulk'.

For common rock material, \kappa\, ~ 10-6 m2∙s-1.

Thermal diffusivity of air at 300 K is 0.000024 m2/s.

For a plot of thermal diffusivity of air as a function of absolute temperature see James Ierardi's Fire Protection Engineering Site

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Thermal_diffusivity". A list of authors is available in Wikipedia.
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