High-rayleigh-number convection in a horizontal enclosure

A review of the literature on natural convection in a horizontal layer heated from below shows the need for reliable data at high Rayleigh number (Ra) to determine the asymptotic Nusselt number (Nu) variation with Rayleigh number. The present study expands the data base by the use of an electrochemical mass transfer technique to determine the asymptotic dependence of the Sherwood number (Sh) on Ra at high Schmidt number (Sc). The results of the present study give Sh = 0.0659 Ra1/3 for Sc ~ 2750, 3 x 109 < Ra < 5 x 1012. Using the heat-mass transfer analogy, this indicates the high Prandtl number variation of Nu with Ra.