# Thermal diffusivity

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In heat transfer analysis, thermal diffusivity (symbol: $\alpha\,$, but note that the symbols κ, D, and k are all commonly used) is the thermal conductivity divided by the volumetric heat capacity. It has the SI unit of m²/s.

where:

The denominator of the thermal diffusivity expression above, $\rho c_p\,$, can be identified as the volumetric heat capacity with the SI unit of J/(m³·K).

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