Measurement methods of bubble and molten metal flow characteristics
in materials processing
In many materials refining processes gas is injected into the molten metal bath of the processes to agitate the bath, and hence, homogenize the bath temperature and chemical compositions. The dispersion of bubbles and molten metal flow induced by the bubbles are responsible for the efficiency of the processes. An electroresistivity probe is usually used to measure the bubble characteristics represented by bubble frequency, gas holdup (void fraction), mean bubble rising velocity and mean chord length. This kind of probe is applicable to molten metal baths of a temperature up to 1873 K. On the other hand, it is very difficult to measure the mean velocities and turbulence components of molten metal flow at very high temperatures. The mean velocities of molten metal flows can be measured using a reaction probe or a Karman vortex probe even if the molten metal temperature is 1873 K as long as the surface flow on the bath is concerned. However, there exists no reliable velocimeter capable of measuring the turbulence components of molten metal flows at a temperature above 400 K. Below 400 K the Vives probe, i.e., magnet probe is widely used. In this paper some experimental results of the bubble and molten metal flow characteristics in a cylindrical bath agitated by bottom gas injection are introduced. The bath is filled with mercury, Wood's metal, molten copper or molten pig iron. Also, X-ray fluoroscopic observation of bubbles in a molten pig iron bath is discussed.