On the Detection and Selective Separation of Inclusions in Liquid Metal Cleanliness Analyzer (LiMCA) Systems

A new design of electric sensing zone (ESZ) probe for the liquid metal cleanliness analyzer (LiMCA) system is proposed, which comprises a contoured orifice and a co-axially built cylindrical extension. This extension is used to collect larger particles whose sizes are larger than the diameter of sensing zone orifice, resolving the orifice blocking problem. A generalized mathematical model was developed for the motion of particles entrained in liquid metals flowing into this newly designed probe. The results showed that the separation of larger from smaller particles is affected by the applied electric current, orifice size, orifice length, orifice shape, extension length, and radius, as well as mean fluid velocity through the orifice. Increasing the electric current, or decreasing the orifice size, is predicted to lower the pass-through fraction of particles of all sizes, but the effects are much greater for larger particles. A longer orifice length gives rise to a lower pass-through fraction, the effect diminishing as the ESZ length increases up to 0.5 mm. The shape of the orifice has little effect on the pass-through fraction of the particles, but it is critical that the entrance to the orifice be smooth in order to prevent the generation of recirculation zone inside the orifice. Increasing the radius of the extension piece increases pass-through fraction of small particles, but decreases that of larger ones. Moreover, the fractional pass-through of inclusions also increases with the decrease of extension length and increase in mean fluid velocity through the orifice. The separation of particles of different density with this newly designed probe can only be achieved when the difference in density is dramatic. Design of probes for magnesium and steel LiMCA is proposed for detecting particles below the detection limit of conventional probes.