Rayleigh Number

A dimensionless number used in heat transfer in general and free convection calculations in particular. It is equivalent to (Gr.Pr).

Ra = (L³ rho² g beta (T₂-T₁) C_P) / (mu k)

Ra = (L³ rho g beta (T₂-T₁)) / (mu alpha)

alpha: thermal diffusivity, beta: coefficient of expansion, C_P: heat capacity, (T₂-T₁): temperature difference, g: gravitational acceleration, k: thermal conductivity, L: characteristic length, mu: viscosity, rho: density