X-ray radioscopic visualization of bubbly flows injected through a top submerged lance into a liquid metal

We present an experimental study on the formation and behaviour of a liquid metal bubbly flow arising from a downward gas injection through a top submerged lance (TSL). A visualization of the bubble dynamics was achieved by the X-ray radiography combined with high-speed imaging. The experiments were carried out in a parallelepiped container (144×144×12 mm3) using GaInSn, a ternary alloy that is liquid at room temperature. The gas flow rate Qgas was adjusted in a range between 0.033 and 0.1 l/s. Three different injection positions were considered with respect to the submergence depth L. X-ray images allow for a characterization of the flow regimes and provide the properties of the individual bubbles such as size, shape and trajectory. Formation and entrainment of smaller gas bubbles are observed at the free surface. These small bubbles can be trapped in the fluid for a long time by recirculation vortices. Bubbles size distributions are determined for different Qgas. The bubble detachment frequency is measured as a function of Qgas and L. The results are compared with previously published data for water. The X-ray radiography offers an effective method for determining the local void fraction and allows for an estimation of the bubble volume.