A multi-beam ultrasonic pulse Doppler method (UDM) has been developed for a new type of flow metering system. Our final purpose is to combine this method with conventional time-of-flight ultrasonic flow meter (TOF) as a hybrid ultrasonic flow metering system for an accurate flow rate measurement of reactor feed water or recirculation water in nuclear power plants. The ultrasonic pulse Doppler method has the capability to obtain instantaneous velocity profiles along an ultrasonic beam. In order to measure flow rate with conventional flow meter, flow must be fully developed and stable, therefore a long straight pipe is necessary upstream of measurement point. In actual industrial plants, however, it is difficult to secure long straight line. The principle of the UDM flow metering system is based on the integration of an instantaneous velocity profile over a pipe diameter. Hence, the multi-beam system is expected to eliminate installation problems such as entry length, and also to follow transmit flow rate precisely by increasing the number of ultrasonic transducers.
