Thermal diffusivity
From Wikipedia, the free encyclopedia
In heat transfer analysis, thermal diffusivity (symbol: α) is the ratio of thermal conductivity to volumetric heat capacity.
where:
- k is thermal conductivity (SI units: watts per metre-kelvin, W∙m-1∙K-1)
- ρcp 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, 
10-2 cm2∙s-1.
For a plot of thermal diffusivity of air as a function of absolute temperature see James Ierardi's Fire Protection Engineering Site
