Definition:  quantity of dimension 1 characterizing the heat transfer by natural convection in a fluid, defined by $Gr=\frac{{l}^{3}g{\alpha}_{V}\text{\hspace{0.05em}}\Delta T}{{\nu}^{2}}$, where l is a specified length, g is acceleration of free fall, α_{V} is cubic expansion coefficient, ΔT is thermodynamic temperature difference, and ν is kinematic viscosity
