Frequency Modulated Ultrasonic Doppler Method for Velocity and Position Measurement of Bubbles

The accurate measurement of velocity and position of bubbles in industrial multiphase flow plays an important role in the study of bubble dynamics, which has great significance for the production efficiency improvement and production safety assurance. With advantages of non-intrusive sensor structure, low cost, no radiation, and applicability for opaque fluids of ultrasonic sensing technique, a frequency modulated ultrasonic Doppler (FMUD) method is proposed to simultaneously measure the velocity and position of dispersed bubbles. Using a linear frequency modulated continuous wave as the excitation signal, the measurement principle of bubble’s velocity and position is derived. Two-dimensional fast Fourier transform (2-D FFT) is adopted to demodulate the frequency information in both the range and velocity dimensions. Considering the flow characteristics of bubbles, the sensor structure with two piezoelectric chips is designed, and the modulation parameters of the excitation signal, including frequency modulation period, bandwidth, and quantity of periods, are carefully selected. A dynamic experimental platform is built to obtain test data under different flow conditions. Compared with the referenced observations from a high-speed camera, the velocity and position of the bubble extracted from the range-Doppler image using 2-D FFT are accurate, indicating the effectiveness of the proposed method.