NONINTRUSIVE DYNAMIC FLOWMETER.

An ultrasonic dynamic flowmeter which combines nonintrusiveness, fast response, high accuracy and high resolution, was designed for use with cryogenic liquids and water. The flowmeter was designed to measure to 1% accuracy, the dynamic (1 to 100 Hz) as well as the steady flow velocity, averaged over the pipe area. The nonintrusive requirement is satisfied by using the vertically polarized component of obliquely incident shear waves, generated by transducers mounted outside the conduit. Compared to obliquely incident longitudinal waves, the choice of obliquely incident shear waves typically doubles the solid/liquid energy transmission coefficient, and doubles the refracted angle in the liquid. Calculations showed that one path was sufficient to obtain the area-averaged measurement of dynamic flow velocity to 1% accuracy. The electronic measuring system employs two different frequencies, each near 1 MHz. These frequencies are transmitted continuously, one upstream and the other downstream, over a common path. The frequencies are servoed such that the phase in each direction is maintained constant. By means of subtracting the two voltages corresponding to the two frequency deviations, an output signal is produced which is proportional only to fluid velocity and is independent of variations in sound speed.