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

T. Lappan¹ - M. Sarma¹ - S. Heitkam^{1, 2} - P. Trtik³ - D. Mannes³ - K. Eckert^{1, 2} - S. Eckert¹

¹ Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
² Institute of Process Engineering and Environmental Technology, Technische Universität Dresden, 01062 Dresden, Germany
³ Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland

Abstract
Ladle metallurgical treatment affects the chemical composition and impurities in molten steel. To remove non-metallic inclusions, gas injection into the ladle and intense stirring by means of bubble 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 metals at room temperature. We apply neutron radiography as imaging technique for the particle-laden liquid metal flow around a cylindrical obstacle of 5 mm in diameter, which is motivated by 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 closed liquid metal loop of 30 mm × 3 mm rectangular cross-section is filled with the low-melting gallium-tin alloy. Gadolinium oxide particles of 0.3 to 0.5 mm in size are employed because of their superior neutron attenuation compared to the liquid gallium-tin alloy. The neutron image sequences visualize the particle trajectories in the opaque liquid metal with a high temporal resolution at the 100 fps imaging frame rate. Up- and downstream the cylindrical obstacle, we analyze the velocity field as a function of the pump rotational rate 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 pressure drop in the liquid metal loop and particles' buoyancy. In the further analysis of these neutron image data, we will focus on the fluid flow in the wake of the cylindrical obstacle. Figs 9, Refs 23.