Surface Tension and Marangoni Convection of Molten NaOH

The surface tension of molten NaOH was measured by means of the maximum bubble pressure method under the various temperature conditions. The measured value has a maximum at T=723.1 K (T*), which shows somewhat low temperature compared to that of Nakamura et al(10). The two distinct temperature coefficients of surface tension (==σ/=T) with different signs were determined at the lower temperature (TT*), but these values are much smaller than those reported by Nakamura et al(10). Two dimensional numerical calculations were also conducted to simulate flow patterns due to thermal Marangoni convection formed in a small molten NaOH bridge under the various thermal conditions. By using the measured values of surface tension, the numerical results succeed in reproducing the observed visualiged flow cell patterns, and revealed that the different multi-roll cell flow patterns are distinguishably formed in the bridge depending upon the surface temperature distribution.