| Summary: | A transit time type ultrasonic flowmeter was tested with two different reflected pulse trajectories in flowing air at ambient conditions against an orifice meter. The flowmeter was designed to be highly accurate, to require minimal excavation for installation (both transducers to be placed on the upper surface of the pipe), and to require no service shutdown for installation or calibration. The two trajectories were two successive tilted diameters with a single reflection, and three successive tilted midradius chords with two reflections. High frequency (100 kHz) narrowband pulses were used. Both ultrasonic flowmetering configurations were tested in 12 inch pipe in fully developed turbulent flow, and in the abnormal flow downstream of a 90 degree elbow. The velocity range was 5.5 fps - 25 fps. The triple midradius chord configuration performed extremely well, with maximum errors of 1.3, and 2.0 percent of reading, in the normal and abnormal flows, respectively. The double tilted diameter configuration gave maximum errors of 7.2, and 9.3 percent of reading in the normal and abnormal flows, respectively. Recommendations for field testing of the two ultrasonic configurations are made.
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