EXPERIMENTAL STUDY OF GALLIUM DROPLET IMPACTING ON SOLID WALL UNDER THE STRONG MAGNETIC FIELD

In the electromagnetic metallurgy processing of materials and the magnetic confinement fusion device, the impact process of metal droplet under the influence of magnetic field and substrate temperature shows complex dynamic characteristics. The spread and rebound characteristics of liquid gallium droplet impacting isothermal and sub-cooled substrate under horizontal magnetic field were studied experimentally. High speed camera is used to capture the change of droplet profile during impact. The maximum spreading factor under different magnetic field strength, impact velocities and substrate temperatures, the maximum height in rebound process, the radius and velocity of secondary droplet are obtained through image processing. The impact velocity increases from 0.45 m/s to 1.8 m/s, and the magnetic field intensity increases from 0 T to 1.6 T. The substrate temperature is 30 °C, −20 °C and −10 °C. The effects of magnetic field and substrate temperature on droplet spread and rebound are analyzed. The experimental results show that the variation of the maximum spreading factor of droplet impacting on the isothermal and sub-cooled substrate is in good agreement with the theoretical prediction. Under the condition that the droplet impacts the isothermal wall, different rebound phenomena occur under different We numbers. The magnetic field inhibits the droplet spreading parallel to the magnetic field and the generation of secondary droplet, while the magnetic field has a elongation effect on the droplet spreading parallel to the magnetic field direction in the rebound process. When the droplet impacts the sub-cooled substrate, within a certain range of We number, the secondary droplet separation will also happen. At this time, the velocity of secondary droplets is smaller. The enhancement of magnetic field and the increase of We number will weaken the oscillation of the droplet in the height direction, accelerating the solidification process.