It represents how fast heat diffuses through a material and has units m2/s. In other words, it is the measure of thermal inertia of given material. Thermal diffusivity is usually denoted α and is given by:
As can be seen it measures the ability of a material to conduct thermal energy (represented by factor k) relative to its ability to store thermal energy (represented by factor ρ.cp). Materials of large α will respond quickly to changes in their thermal environment, whereas materials of small α will respond more slowly (heat is mostly absorbed), taking longer to reach a new equilibrium condition.
Thermal Diffusivity in Heat Conduction Equation
Constant Thermal Conductivity
This equation can be further reduced assuming the thermal conductivity to be constant and introducing the thermal diffusivity, α = k/ρcp: