Thermal diffusivity: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries.

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

Encyclopedia of Chemistry

See also