Thermal_diffusivity

Thermal diffusivity

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

$\alpha = {k \over {\rho c_p}}$

where:

$k\,$ : thermal conductivity (SI units : W/(m K) )
$\rho c_p\,$ : volumetric heat capacity (SI units : J/(m³K) )
$\rho\,$ : density (SI units : kg/(m³) )
$c_p\,$ : specific heat capacity (SI units : J/(kg K) )

The SI units for thermal diffusivity is m²/s.

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, $\alpha\,$ ~ 10^-6 m²/s.

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