This work proposes clad buffer rods driven by shear transducers as the main building block of contrapropagating ultrasonic flowmeters for high temperature application. It is demonstrated that the superior signal-to-noise ratio exhibited by clad buffer rods (compared with the reported nonclad counterparts) improves precision in transit time measurements, leading to more accurate flow speed determination. In addition, it is shown that clad buffer rods generate specific ultrasonic signals for temperature calibration of flowmeters, allowing temperature variation while still measuring accurately the flow speed. On the basis of these experimental results, a contrapropagating ultrasonic flowmeter was designed and installed in a heater machine for flow speed measurements of hot oil at temperatures near 130°C. For a temperature variation of 3°C, the difference between upstream and downstream ultrasonic transit times, which is proportional to the flow speed at a given temperature, was measured within 1 ns accuracy.

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