Abstract
The characteristics of particle entrainment from free surface or bottom wall into mechanically agitated water have been studied to clarify the inclusion behavior in liquid metal. The critical agitation speed, nc at which a 50% of particle is entrained into bulk water is measured under steady state by using buoyant particles (glass balloon and silica balloon) and sedimental particles (glass bead). It is found that the dependence of nc on the particle diameter, dp, is different between the buoyant and the sedimental particle. For the case of the buoyant particle, nc is independent of dp, whereas for the sedimental particle nc increases with increasing dp, . To account for this difference, two transition times are investigated. One is the entraining time, t1, which is the time needed to reach a steady state after a sudden imposition of agitation with various speeds. The other is the floating/sinking time, t2, which is the time required to reach a steady state after a sudden decrease in agitation speed from a high speed achieving uniform particle dispersion to lower agitation speeds. It is thought that the balance between t1 and t2 should determine the amount of entrained particles in bulk water under steady-state experiments. For the case of the buoyant particle, the dependencies of t1 and t2 on dp are almost same, so that the value of nc does not depend on dp. On the other hand, for the case of the sedimental particle, the dependence of t1 on dp is smaller than that of t2, so that nc increases with increasing dp. By the VTR observation of the particle entrainment from the free surface or bottom wall, particles are found to be entrained mainly by vertical vortices formed in the agitation vessel.
