Thermal diffusivity

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In heat transfer analysis, thermal diffusivity (symbol: <math>\alpha</math>) is the ratio of thermal conductivity to volumetric heat capacity.

<math>\alpha = {k \over {\rho c_p}}</math>

where:

• k is thermal conductivity (SI units: watts per metre-kelvin, W∙m^-1∙K^-1)
• ρc_p is the volumetric heat capacity (density times specific heat capacity; 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, <math>\alpha \approx</math> 10^-2 cm²∙s^-1.

See also

• heat capacity
• specific heat capacity
• heat equation