![[Graphics:../Images/thermal_bl_gr_80.gif]](../Images/thermal_bl_gr_80.gif){kind=small}
= 2 + ![[Graphics:../Images/thermal_bl_gr_81.gif]](../Images/thermal_bl_gr_81.gif){kind=small}
.(See page 504 of I &D.)
The Nusselt and Rayleigh numbers are based on the sphere diameter. Thus this correlation does have
![[Graphics:../Images/thermal_bl_gr_82.gif]](../Images/thermal_bl_gr_82.gif){kind=small}
in agreement with the scaling of the boundary-layer equations. Note that Ra≡ Gr Pr.
There is a recommended correlation (from Churchill) for free convection heat transfer from a sphere: = 2 + .
(See page 504 of I &D.)
The Nusselt and Rayleigh numbers are based on the sphere diameter. Thus this correlation does have in agreement with the scaling of the boundary-layer equations. Note that Ra≡ Gr Pr.