): Just as the Reynolds number governs forced convection, the Grashof number is the "heartbeat" of natural convection. It represents the ratio of the buoyancy force to the viscous force. The Rayleigh Number (
∇⋅v = 0
$$ Ra_L = \fracg \beta (T_s - T_\infty) L^3\nu^2 Pr $$ ): Just as the Reynolds number governs forced