| Multiphase flow is commonly encountered and of paramount significance in all aspects of scientific research,industrial production,environmental protection,medical treatment and daily life.Multiphase flow is different from single phase flow and more complicated.It has the inter-phase interface with spatial and temporal non-uniform distribution,the nonlinearity response,the inter-phase relative velocity,inter-phase slip and other flow characteristics,so multiphase flow parameter measurement is still a relatively difficult subject.With the scientific progress and industrial development,accurate measurement of multiphase flow parameter has significance on the optimization of production process and equipment.It is of great importance to ensure the security and stability of multiphase flow production process.Phase fraction of multiphase flow is a significant indicator to multiphase flow characterization,the process control and optimization.In order to accurately measure the phase fraction of multiphase flow by ultrasonic method,based on studying the ultrasound propagation mechanism in typical flow patterns of oil-gas-water multiphase flow,the ultrasound transmission and multiple scattering characteristics in multiphase flow are analyzed and explained theoretically.A prediction model based on the ultrasound attenuation and transit time mechanism is presented to estimate the phase fraction in oil-water two-phase flow and stratified oil-gas-water three-phase flow.A corresponding ultrasonic technology testing method and system are established to realize the accurate measurement of the phase fraction in oil-gas-water multiphase flow.The method improves the nonlinear response and expands the application range of measurement.The main works accomplished are as follow:(1)Based on the summary of studies on multiphase flow phenomenon,flow parameters and main test methods,the major difficulties of parameter measurement in multiphase flow by ultrasound technology are analyzed.For the nonlinearity response and the limited measuring range in ultrasound method,a prediction model is proposed to estimate the phase fraction based on ultrasound propagation mechanism in multiphase flow.(2)Aim at ultrasonic technology application in the two-phase flow measurement,geometric models of ultrasonic sensor are set up by numerical simulation technique.By investigating the distribution features of ultrasonic sensor sensitivity field,transmit frequency and physical dimension of ultrasonic transducer are optimized comprehensively.Transducer installation and experimental research are carried out on the selected ultrasonic transducer parameters.(3)To study the influence of the phase distribution and phase fraction on ultrasonic attenuation in typical flow pattern of oil-water two-phase flow,the changes of the ultrasonic attenuation in oil core flow,stratified flow and dispersed flow with uniformly distributed droplets are numerically simulated based on the finite element analysis method.The ultrasound transmission and propagation regularity in non-emulsified oil-water two-phase flow is analyzed.Simulation experiments show that phase distribution and phase fraction have great influence on the ultrasonic attenuation coefficient,and there are certain regularity between them.(4)Mechanism models describing phase fraction with the ultrasound attenuation coefficient were established by analyzing the interaction between ultrasound and the oil-water two-phase flow with dispersed droplets,by considering scattering attenuation,absorption attenuation and diffusion attenuation.The presented mechanism models give reasonable explanations about the trend of ultrasound attenuation and have solved the nonlinearity of the relationship between ultrasound attenuation coefficient and phase fraction.(5)Based on the mechanism of ultrasound attenuations in the stratified flow and the dispersed flow of oil-water two-phase flow,prediction models are respectively established to estimate the phase fraction.By setting boundary correction coefficient,a unified prediction model based on the physical mechanisms of the ultrasound attenuation was presented,which includes the ultrasound attenuation mechanism in both the stratified flow and the dispersed flow of oil-water two-phase flow.A transducer array and a measuring system were designed and tested on a multiphase flow loop with dynamic experiments.The findings show that the mechanism prediction model basically meets the requirement of the actual test and expands the measurement range of the phase fraction.The ultrasonic method provided basic foundations for the phase fraction estimation of oil-water two-phase flow by using ultrasound attenuation technique.(6)For purpose of phase fraction measurement in oil-gas-water three-phase flow,the height of the liquid level was detected using transit time of ultrasound in the reflection of the gas-liquid interface,while the oil phase fraction in the reflection path is calculated according to the ultrasound attenuation.A prediction model for phase fraction measurement of three-phase flow was established based on transmission attenuation and transit time in the process of horizontal flow with the actual distribution of the gas and liquid phases.The simulation experimental results of oil-gas-water laminar flow,plug flow and slug flow,show that the proposed method and the established model can accurately obtain the height of the gas-liquid interface and detect the plug position so that measure oil,gas,water phase fraction of oil-gas-water three-phase flow. |
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