Simple Theory for Laminar Natural Convection Heat Transfer (and Film Boiling and Film Condensation) or Where Do the Nusselt and Rayleigh Numbers Come From?

It is difficult to give a scientific introduction to convective heat transfer. Accurate analysis is very lengthy. Dimensional analysis gives no physical insight and the meaning of the dimensionless groups is sometimes obscure. The present paper gives a much simpler analysis for natural convection on a vertical plate which quickly arrives at the Nusselt and Rayleigh numbers. In addition virtually the same analysis gives the heat transfer rate in film condensation and film boiling.