In the iron and steel manufacturing industries, efforts are being made to achieve carbon neutrality
by 2050, and the transition from a coal-based steelmaking process to that utilising renewable energy
is being pursued. An alternative process in which directly hydrogen-reduced iron is melted in an
electric furnace is being investigated. It is known that foaming slag reduces heat loss from the steel
bath in electric arc furnace, but iron loss due to the suspension of steel particles in the slag is
indispensable. To improve the separation of steel particles from the slag, the control of the slag
viscosity is important.
Although the slag viscosity has been extensively studied, in those studies the slag was considered
to be a simple liquid. However, in actual operations, slag is a multiphase fluid consisting of solid, gas
and liquid phases. Therefore, in this study, by measuring the sedimentation velocity of titanium,
stainless steel and glass spheres in an aqueous glycerin solution containing bubbles generated by
the reaction between NaHCO3 and C2H2O4, the apparent viscosity of the gas-liquid fluid was
evaluated based on Stoke’s law. It was found that the apparent viscosity of the gas-liquid fluid is
larger than the viscosity of liquid phase and depends on both the bubble volume ratio in solution and
the density of the falling solid sphere, and the apparent viscosity was different from that previously
obtained by the rotation method. The apparent viscosity derived from the sedimentation velocity of
solid spheres changed depending on the specific gravity of the ball. This is because the apparent
viscosity is derived from the velocity of a ball falling in a static bubble in this method, whereas that is
derived from the force applied by a stationary flow in the rotational method.