Oil Fraction Measurement of Nonuniform Dispersed Oil–Water Two-Phase Flow Based on Ultrasonic Attenuation

Oil volume fraction determination is important to the transportation and separation of oil-water dispersed flow in petroleum industry, for which ultrasound method is suitable with the advantages of good penetration and low cost. Existing ultrasonic attenuation methods are based on homogeneous media for the determination of phase fraction without considering the effect of inhomogeneity on attenuation. In this paper, the fractal approach is introduced to modify the acoustic attenuation model by characterizing the inhomogeneity of the dispersed phase in pipe flow, which establishes the relationship between multi-frequency attenuation and droplet size distribution. Then, an improved covariance matrix adaptive evolutionary strategy (CMA-ES) based on the established attenuation model is proposed to estimate oil volume fraction, which combines restart strategy with local search strategy to enhance the search performance and avoid falling into local optimum. Moreover, a demodulation method based on swept-frequency chirp is designed for the time-varying dispersed oil-water pipe flow to quickly obtain the multi-frequency attenuation. The effectiveness of the fractal-based modified attenuation model and the improved CMA-ES is verified by numerical simulations and flowing experiments. The experimental results at different oil volume fractions and flow rates indicate that the fractal-based modified attenuation model can effectively reduce the impact of non-uniform distribution of dispersed phases on the attenuation measurement, and thus effectively improve the measurement accuracy of the oil volume fraction, especially for the dispersed flow in the horizontal pipe.