A novel, inexpensive and rugged probe for measuring gas bubbles in liquid metals

A new probe for detecting gas bubbles in liquid metals has been tested in the laboratory in a cold model and finally in liquid aluminum at the Alcoa Technical Center. The probe is rugged and inexpensive consisting of a narrow alumina tube connected to an inexpensive microphone by a plastic tube. The tip of the alumina tube is immersed in the liquid and a flow of argon down the tube creates a stream of tiny argon bubbles at that tip. Those bubbles are "heard" by the microphone which relays its signal to a laptop computer. When a large bubble, such as one created by an immersed impeller or wand, reaches the probe tip the sound (pressure fluctuations) detected by the microphone changes and the change is visible at the laptop. As a result of work in our laboratory, we have learned that the pressure fluctuations, resulting from a cup bubble passing the probe tip, are due to the bubble wake.