text: The Nusselt number may be obtained by a non-dimensional analysis of Fourier's law since it is equal to the dimensionless temperature gradient at the surface:
  :, where q is the heat transfer rate, k is the constant thermal conductivity and T the fluid temperature.
  Indeed, if:  and 
  we arrive at
  then we define
  so the equation becomes
  By integrating over the surface of the body:
  where .