| A hydrate liquid film is often formed on the wall of natural gas transportation pipelines.The natural gas hydrate in the liquid film is prone to agglomerate and block pipelines,valves,and other equipment,which not only causes economic losses,but may also cause safety accidents.The study of a method for measuring the thickness of the hydrate-bearing liquid film in the pipeline is of great significance for the safe and efficient transportation of natural gas and ensuring the normal operation of the pipeline.This project adopts a measurement scheme that combines the resistance method and the ultrasonic transit time method to design and optimize the concave electrical-acoustic composite sensor for the measurement of the thickness of the hydrate-bearing liquid film in the horizontal pipeline.Through the development of three-dimensional numerical simulation and the hydrate-bearing liquid film in the test experiment,the influence of the spatial distribution shape and volume holdup of the hydrate in the liquid film on the response characteristics of the composite sensor was studied,and the relationship model between the sensor response and the volume holdup of hydrate,the conductivity of water and the thickness of the liquid film were discussed.To realize the measurement of the thickness of the hydrate-bearing liquid film in the pipeline.Through the research of this subject,it provides a new method for the measurement of hydrate containing liquid membrane parameters,provides a theoretical and model basis for the development of related experiments and the optimization of sensor structure parameters,and provides a reference for the research of complex liquid film parameter measurement methods in engineering applications.The method of numerical simulation is used to determine the axial length of the geometric model of the pipeline with the sound pressure level change in the pipeline as the index;the transmission efficiency,emission performance and receiving sensitivity of the ultrasonic transducer are used as indexes,and the acoustic measurement part of the composite sensor The matching layer,piezoelectric wafer and back-scale structure have been optimized.The research results show that:(1)The space area formed between the center electrode A and the electrode ring C of the coaxial double ring electrode is a high-sensitivity area;(2)The sound field has an effective coverage area along the pipe axis,and the sound pressure exceeds this range.(3)Under the condition that the excitation signal frequency is 1MHz,the thickness of the piezoelectric wafer is 2mm and the diameter is 15 mm,which can ensure the highest electrical-mechanical conversion efficiency of the sensor;Adding matching layer material can improve the emission performance and receiving sensitivity of acoustic measurement part.Adding backing material can improve the detection resolution and output waveform,but also sacrifice part of the detection sensitivity.Based on the above optimized sensor numerical model,the thickness of the hydratebearing liquid film of 0.80mm～12mm was simulated and measured,and the hydrate particle size,particle spacing,volume fraction and spatial distribution morphology were investigated for electrical and acoustics.The influence law of response characteristics,the research results show:(1)The hydrate particle size,particle spacing,volume holdup and spatial distribution shape jointly determine the measured value of liquid film resistance,where the particle size and volume holdup are positive with the measured resistance value.Correlation,the particle spacing is negatively correlated with the measured resistance;(2)When the hydrate distributed in the high-sensitivity measurement area changes,it will have a greater impact on the output signal of the sensor,and when the hydrate far away from this area changes,it will affect the sensor.(3)Ultrasonic transit time method cannot accurately measure the thickness of the liquid film of hydrate particles,but it can measure the thickness of the liquid film of the hydrate suspension layer more accurately.Based on the above optimized design,an electrical-acoustic composite sensor was fabricated,and an electrical-acoustic joint measurement experiment system for the thickness of the hydrate-bearing liquid film was designed and built.The simulation experiments on the formation and decomposition of the hydrate in the liquid film in the horizontal pipeline were carried out,and the hydration was established respectively.The relationship model between the volume content of the material and the measured resistance of the liquid film,the thickness of the liquid film and the measured resistance of the liquid film,and the relationship between the thin liquid film-acoustic characteristic parameters and the thick liquid filmacoustic characteristic parameters are discussed.The research results show that:(1)The hydrate suspension layer is mainly distributed in the upper layer of the liquid film,with a smooth layered distribution on the upper surface and a rough granular distribution on the lower surface;(2)When the thickness of the liquid film is fixed,the measured resistance of the liquid film has a positive correlation with the volume fraction of hydrate,and the growth rate of the resistance of the liquid film with the volume fraction of hydrate is faster when the volume fraction of hydrate is 50% ～ 70%,and the growth rate of the resistance of the liquid film with other volume fractions is slower;(3)Under the same volume fraction and liquid conductivity,when the thickness of the liquid film is in the range of 2.50 ～ 3.50 mm,the resistance of the liquid film decreases rapidly with the increase of the thickness of the liquid film;When the thickness of the liquid film is higher than 3.40 mm,the ultrasonic transit time method can be used to measure the thickness of the liquid film.The thinner the hydrate layer is,the greater the influence on the interpretation of the echo head wave time is. 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