Published online by Cambridge University Press: 22 June 2001
Using the Hopf–Doering–Constantin decomposition, we derive upper bounds on the vertical heat flux in closed containers. It is found that the original bound of Doering & Constantin (1996) for Nusselt number as a function of Rayleigh number, Nu [ges ] √R/4, holds, at the very least, asymptotically as R → ∞ under reasonably diverse experimental settings.