Thermal Diffusivity:

It is defined as the ratio of thermal conductivity of body to its heat storage capacity.

$α=K_ρ.C_p$

Where, $ρ, C_p$ is heat storage capacity per unit temperature difference per unit volume.

Significance:

• The larger the value of α, the faster will the heat diffuse through the material and its temperature will change with time.
• This will result either due to a high value of conductivity K or a low value of heat capacity ρ.Cp.
• A low value of heat capacity means the less amount of heat entering the element, would be absorbed and used to raise its temperature and more would be available for onward transmission.
• Metals and gases have relatively high value of α and their response to temperature changes is quite rapid.
• The non metallic solids and liquids respond slowly to temperature changes because of their relatively small value of thermal diffusivity.