# Thermal Diffusivity

Written by Jerry Ratzlaff on . Posted in Thermodynamics

Thermal diffusivity, abbreviated as $$\alpha$$ (Greek symbol alpha), is a measure of the transient thermal reaction of a material to a change in temperature.

### Thermal Diffusivity formula

$$\large{ \alpha = \frac{ k }{ \rho \; Q } }$$

$$\large{ \alpha = \frac{ Fo \; l_c^2 }{ t } }$$     (Fourier number)

$$\large{ \alpha = Le \; D_m }$$     (Lewis number)

$$\large{ \alpha = \frac{ \nu }{ Pr } }$$     (Prandtl number)

$$\large{ l_c = \frac{ We \; \sigma }{ \rho \; v^2 } }$$     (Weber number)

Where:

$$\large{ \alpha }$$  (Greek symbol alpha) = thermal diffusivity

$$\large{ l_c }$$ = characteristic length

$$\large{ \rho }$$  (Greek symbol rho) = density

$$\large{ Fo }$$ = Fourier number

$$\large{ \nu }$$  (Greek symbol nu) = kinematic viscosity

$$\large{ Le }$$ = Lewis number

$$\large{ D_m }$$ = mass diffusivity

$$\large{ Pr }$$ = Prandtl number

$$\large{ Q }$$ = specific heat capacity

$$\large{ \sigma }$$  (Greek symbol sigma) = surface tension

$$\large{ k }$$ = thermal conductivity

$$\large{ t }$$ = time

$$\large{ v }$$ = velocity

$$\large{ We }$$ = Weber number