50 巻 (2014) 5 号 p. 404-410
Ultrasonic vortex flowmeters are often used in the semiconductor manufacturing process. For better performance of the fluid control, it is desired to improve the signal processes of the vortex flowmeters. However, in practical terms, it is difficult to measure the flow velocity of the gas-liquid two-phase flow by using an ultrasonic vortex flowmeter. In order to examine the bubble behaviors behind the vortex shedder of the vortex flowmeter, visualization studies were performed under several different conditions in terms of the pipe diameter (D) and the void fractions (0.1%-2.1%), using the test fluids of tap water and air at room temperature. We found that the measurement of the bubble-laden flow was difficult for D=4.5 mm. For D≤8.5 mm, the P-FFT analysis based on the pre-multiplied energy spectra was proposed to extract accurately the Kármán-vortex frequency in the bubble-laden flow. The P-FFT analysis with a low-pass filter allows us to eliminate the low frequency from the measurement signal and to obtain successfully the liquid velocity even in a rather wide void-fraction range of the gas-liquid two-phase flow.