Design And Application Of Pulse-wave Ultrasonic Doppler Two-phase Flow Velocity Measurement System

Pulse Wave Ultrasonic Doppler(PWUD)is a method for measuring velocity using the ultrasonic Doppler principle.It has the advantages of non-intrusion,no radiation,and low cost.The oil-water two-phase flow is widely existed in the petrochemical industry.The acquisition of its velocity distribution in the pipe is significant for the accurate measurement of flow velocity and the study of flow structure.In order to obtain the velocity distribution of horizontal oil-water two-phase flow under different flow conditions and establish the flow velocity profile model,a pulse wave ultrasonic Doppler measurement system based on industrial bus standard was designed.The horizontal oil-water two-phase flow experiments under various flow conditions were carried out.And the flow velocity profile of the oil-water two-phase flow in the horizontal pipe was analyzed and modeled by the measured data.The main research work of the project includes:(1)Scheme of pulse wave ultrasonic Doppler two-phase flow velocity measurement system.According to the pulse wave Doppler measurement principle and the propagation characteristics of the ultrasonic wave in the oil-water two-phase flow,the excitation voltage,frequency and pulse repetition frequency of the pulse wave are determined,and the structure of the ultrasonic probe is determined according to the characteristics of the pulse wave.According to the Doppler principle,a demodulation module is designed to extract Doppler information from the ultrasonic echo signals.(2)Design of PWUD measurement system.Since the reflectivity between the oil-water two-phase interface is very low,a higher and stable 1 MHz excitation signal is required to ensure the signal-to-noise ratio of the received signal,and an external high-voltage constant voltage source and a complementary MOSFET are used to form a high-voltage pulse excitation module of the system.The multiplier and the FIR low-pass filter are implemented by the FPGA to form digital multiplication demodulation,which is used as a signal processing module of the system for extracting Doppler frequency shift information.In order to meet the Nyquist sampling theory and high-speed transmission requirements,the system’s data transmission module is designed based on the CPCI industrial bus standard,and the data transmission rate is 10 MHz.(3)Horizontal oil-water two-phase flow velocity profile experiment.The horizontal oil-water two-phase flow experiment was designed and carried out,and the two-phase flow velocity distribution in the whole content range was obtained.The flow rate at the inlet of the oil-in-water flow pattern is used as a reference to verify the measurement accuracy of the system,and the relative error is less than 15%.(4)Oil-water two-phase flow velocity profile modeling.By comparing the measured flow velocity distribution of the two-phase flow with the flow velocity distribution of the single-phase flow,the difference between the two-phase flow velocity distribution and the single-phase flow was illustrated.Using the dimensionless method,a mathematical model of the two-phase flow velocity profile under continuous water and oil continuous conditions was constructed respectively.