Patent ID: 7415893

Claim:
A bubble generator used for a Doppler ultrasonic flowmeter, which measures a flow rate of a fluid to be measured and includes ultrasonic transmitting means for emitting an ultrasonic pulse of a predetermined frequency from an ultrasonic transducer into the fluid to be measured in a fluid pipe along a measurement line; fluid velocity distribution measurement means for measuring a flow velocity distribution of the fluid to be measured in a measurement region by receiving, out of the ultrasonic pulses emitted into the fluid to be measured, an ultrasonic echo reflected in the measurement region; and flow rate computing means for calculating the flow rate of the fluid to be measured in the measurement region based on the flow velocity distribution of the fluid to be measured, comprising: bubble generation means for generating bubbles suitable for a predetermined frequency of the ultrasonic pulse emitted into the fluid to be measured and including a Venturi tube to feed the bubbles into the fluid pipe; and uniform dispersion means for dispersing the bubbles fed uniformly in the pipe and including a negative pressure generating means installed on an upstream side with respect to the ultrasonic transducer, the fluid to be measured sucked from the fluid pipe by said uniform dispersion means is returned into the fluid pipe together with the bubbles fed into the fluid pipe via the Venturi tube, wherein said bubble generator is installed on the upstream side of the fluid pipe with respect to the ultrasonic transducer.