In situ observation and numerical simulation of bubble behavior in CaO-SiO2 based slag during isothermal and nonisothermal processes

Abstract The hot thermocouple technique was used to observe the variation of bubble size in CaO-SiO2 based molten slag at above 1273 K. Considering that the physical properties of gases change with temperature, the effect of cooling rate on the single bubble behavior was studied according to the heat and mass transfer equations. In order to investigate the distribution of pore size in solidified layer, solidification of slag was conducted in laboratory by using a water-cooled detector, and the pore size in the solidified layer was counted under the scanning electron microscope. The heat flux measured by the water-cooled detector was used as boundary conditions to establish a mathematical model that is capable of describing the characteristics of bubble size distribution. Both the calculation and the observations indicate that the time-temperature history is an important factor that could affect the bubble behavior in molten slag. For slag with no Na2SO4, bubbles with large size concentrate on the detector side with high cooling rate, while bubbles with small size are likely to appear on the liquid side with low cooling rate. For slags containing Na2SO4, bubbles with large size mainly distribute on the middle layer of the solid slag film.