1)      Natural convection heat transfer on a surface depends on

a)      Geometry of the surface

b)      Orientation of surface

c)      Variation of temperature on the surface

d)      Thermophysical properties of the fluid involved

2)      Some analytical solutions exist for natural convection, but such solutions lack generality since they are obtained for simple geometries under some simplifying assumptions.

3)      Natural convection heat transfer correlations are usually expressed in terms of the Rayleigh number raised to a constant n multiplied by another constant C, both of which are determined experimentally.