Neutron radiography of particle-laden liquid metal flow driven by an electromagnetic induction pump

Ladle metallurgy treatment affects the chemical composition and the impurities in molten steel. To remove non-metallic inclusions, gas injection into the ladle and intense stirring by bubbly flows are essential in the refining process. This paper reports on a model experiment that provides an insight into the bubble – particle interaction in liquid metal at room temperature. We apply neutron radiography as imaging technique for particle-laden liquid metal flow around a cylindrical obstacle representing a single rising bubble. The experimental setup is tailored to both the measurement principle of neutron transmission imaging and the design of the disc-type induction pump driving the flow. A liquid metal loop of 30 mm x 3 mm rectangular cross section is filled with low-melting gallium-tin alloy. Gadolinium oxide particles (0.3 – 0.5mm) are employed because of their superior neutron attenuation compared to liquid gallium-tin. The neutron image sequences visualise the particle trajectories in the opaque liquid metal with high temporal resolution (100 fps). Up- and downstream the cylindrical obstacle, we analyse the velocity field as a function of the pump’s rotational speed by particle image velocimetry (PIV). The time-averaged particle velocity measured by PIV is lower than the circumferential velocity of the pump’s discs. This velocity deficit arises from the particles’ buoyancy and the pressure drop in the liquid metal loop. In the further analysis of these neutron image data, we will focus on the fluid flow in the wake of the cylindrical obstacle.