Fundamental Study on Application of Ultrasonic Velocimetry to Molten Glass

This paper describes fundamental study intended to apply ultrasonic velocimetry to molten glass. Buffer rod is employed to transmit ultrasound into molten glass. Several ceramics are tested for capability, which regards transmission characteristic and corrosion resistance. Among tested materials, mullite provides perfect wetting with a borosilicate glass and highest transmission ratio. Trailing echo level, which is the level of spurious signal arouse inside buffer rod, is evaluated both numerically and experimentally. Trailing echo level can be improved by using higher frequency of ultrasound. Acoustic field after buffer rod is investigated. Measurement near the buffer rod surface should be avoided due to ununiformed pressure distribution as a normal planner ultrasonic transducer has. Ultrasonic beam become sharp due to absorption on the side wall when buffer rod is equipped. Sound speed in the molten glass is obtained from 1000 °C to 1200 °C. Obtained values are almost constant within this temperature range although small negative slope is observed against temperature. Attenuation coefficient of ultrasound in the molten glass is also measured. The coefficient is well modelled to temperature dependent exponential function. Finally, application of velocimetry via buffer rod is demonstrated. From velocity profiles, maximum measurable range is investigated. Experimental results suggest that velocimetry measurement can be done unless ultrasound energy is attenuated to trailing echo level.