Ultrasonic flow metering is one of flow measurement techniques applicable to low temperature environment. Unlike pipe provers or Coriolis mass flowmeters, ultrasonic flowmeters require waveguides in front of ultrasound sensors. The waveguides can prevent heat conduction from the ultrasound sensors to low temperature liquids, such as liquid nitrogen. The ultrasound sensors can maintain its piezoelectricity within the specified temperature ranges by thermal insulation of the waveguides.

In this study, low temperature testing on a pair of ultrasound sensors was performed to see if ultrasound waves could be transmitted normally through liquid nitrogen. A flowmeter cell with diameter of 300 mm (equivalently, 12”) was used as a container for liquid nitrogen. Three pairs of ultrasound sensors were installed in the flowmeter cell. Fiber-optic sensors were also attached on its inner wall to measure the temperature of liquid nitrogen. As a result, ultrasound waves were successfully transmitted between a pair of ultrasound sensors by using a preamplifier. The fiber-optic sensors could measure the temperature of liquid nitrogen although the sensors were not calibrated by the reference temperature scale at KRISS.

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