Model Of Ultrasonic Sensor For Measuring Gas Holdup In Gas-Liquid Two-Phase Flow

Gas-liquid two-phase flow is widely found in the production process of petroleum exploitation,nuclear reactor,chemical industry,metallurgy and other industrial fields.The gas holdup is an important parameter reflecting the dynamic behavior of gas-liquid two-phase flow,it is closely related to the flow pattern,flow velocity and flow direction of the fluid,and it is an important component of the gas-liquid two-phase flow model.Ultrasonic sensors are widely used in the multiphase flow detection technology,it is significant in academic value and practical application to explore the gas holdup theoretical model of ultrasonic sensor in gas-liquid two-phase flow.In this thesis,the theorical gas holdup model of ultrasonic sensor in gas liquid two-phase flow under different bubble diameter is established.Firstly we use the fluid sampler to obtain the images of gas-liquid two-phase flow and employ the multiscale edge detection algorithm to obtain the bubble diameter parameter.Then we obtain the amplitude attenuation information according to the ultrasonic sensor and obtain the gas holdup parameter by the quick closing value method and conductance sensor,then we build the gas holdup statistical model and theoretical model of ultrasonic sensor.The innovated results of this study are stated as follows:1.The gas holdup theorical model of ultrasonic sensor in gas liquid two-phase bubble flow is established.In this thesis,we find the attenuation law of ultrasonic pulse energy with the gas holdup,and find the ultrasonic attenuation law influenced by the bubble diameter,which shows a piecewise function that presents a segmentation point with gas holdup of 10%.The theoretical model and ultrasonic attenuation information is used to predict the gas holdup and the prediction result is compared with the gas holdup by quick closing valve and conductance sensor,the AAPD is 9.21% and 10.38%respectively,which also shows good gas holdup prediction effect.2.For the bubble diameter parameter in gas holdup theorical model of ultrasonic sensor,we use the multiscale edge detection algorithm to analyze the images of fluid sampler to get the probability density distribution of bubble diameter in different gas holdup flow condition.We find that the main part of bubbles are small diameter bubbles and the large bubbles are less while the gas holdup is low.We also find that bubbles of small bubble diameter and large bubble diameter exist at the same time and are unevenly distributed.We calculate the mean bubble diameter of the bubble at different gas holdup,and provide bubble diameter information for establishing the theorical gas holdup predicting model of ultrasonic sensor.3.The Magnitude-sign detrended fluctuation analysis method is used to analyze the ultrasonic sensor measurement signal from the from the perspective of long-range correlation.While the gas holdup is low,the local and overall self-similarity is low and shows the positive correlation;while the gas holdup is high,the local and overall self-similarity is high and shows the negative correlation.The gas holdup predicting model of ultrasonic sensor is characterized by different bubble diameter indices on the joint plane of magnitude and sign scales.