Natural Convection Heat Transfer with Crust Formation in the Molten Metal Pool

An experimental study has been performed on natural convection heat transfer with and without crust formation in a molten metal pool. Two types of steady-state tests, natural and forced convection coolings of the molten metal pool, were performed in low- and high-aspect-ratio cases. When the natural convection flow is developed in the molten metal pool, the overlying coolant conditions do not affect the crust formation. On the other hand, when the natural convection flow is not developed, the coolant conditions affect the crust formation. The heat transfer rate of cases with crust formation is lower than that of cases without crust formation due to the effect of the crust serving as a thermal barrier. The present experimental results on the relationship between the Nusselt number and Rayleigh number match better with Globe and Dropkin's correlation than any others. With an increase in the crust thickness, the Nusselt number in the metal pool does not rapidly decrease in spite of a rapid decrease in Rayleigh number because the aspect ratio of the metal pool decreases. A new correlation between the Nusselt number and Rayleigh number in the molten metal pool with crust formation has been developed as Nu = 0.0923 (Ra)^0.302 (2 × 10⁴ < Ra < 2 × 10⁷).