Research On Array Capacitance Sensors In Two-phase Flow Parameter Measurement

Gas-liquid two-phase flows exist in the fields of atomic energy engineering,oil and gas transportation,nuclear reactors and chemical industry.Rectangular narrow channels and bar beam channel channels are common structural forms in reactors and heat ex-changers with complex characteristics of flow,phase distribution and heat transfer,which pose greater difficulties for parameter detection.Monitoring of this flow is an urgent need to ensure stable and efficient operation of the system.Compared with the commonly used detection methods,capacitance sensors have a series of advantages such as simple structural design,high resolution,applicability to industrial environments,non-contact measurement and a series of other advantages.Considering that the same volume of bubbles has higher detection accuracy in a smaller effective detection area,for the distribution characteristics of gas-liquid two-phase flow,this paper proposes a design study of array capacitance sensor for gas-liquid two-phase flow parameter detection.The main research contents of this paper are:1.For gas-liquid two-phase flow at home and abroad,the more popular detection techniques such as digital image technology,process chromatography imaging,ray attenuation method,resistance resistance method,etc.are briefly analyzed and compared.2.The relevant parameters of the two-phase flow that affect the void fraction are introduced,the main flow patterns and factors affecting the flow pattern in the vertical direction of the ascending pipe and the horizontal pipe are analyzed,the common methods of flow pattern detection and identification are introduced,the factors affecting the void fraction are analyzed by measuring the void fraction,and the commonly used void fraction mathematical models are introduced: homogeneous flow model and slip ratio model.3.The types of capacitance sensors are analyzed,based on the principle of changing the capacitance value caused by the change of the medium between the plates,the array type capacitance sensor structure is proposed for the vertical rising pipe,and the three-dimensional structure of the array type capacitance sensor is established by using COMSOL Multi-physics simulation software,and the changes of bubble size,electrode spacing,electrode size are analyzed by parametric scanning The relationship between bubble size,electrode spacing,electrode size variation and capacitance value variation is analyzed by parametric scanning to determine the structural parameters of the array capacitance sensor.4.The STM32F103C8T6 is selected as the processor to design the corresponding control module circuit,and the AD7142,a high-precision capacitance digital conversion chip with integrated on-chip environmental calibration,is selected to design the micro-capacitance detection hardware circuit.Visual Studio 2010 software to design the micro-controller program and the upper computer program respectively for data processing,receiving and saving display.5.Build the experimental system platform,test the sensor and hardware circuit,and conduct calibration experiments to determine the initial value of the capacitance sensor when there is only water medium in the measurement channel,and the error between the actual initial capacitance value of 0.746 p F and the theoretical capacitance value of0.737 pf is 0.94%.The capacitance value of the capacitance sensor was tested at different gas content rates by configuring 10 measurement channel samples with the gas content rate increasing from 0 to 100% in order of 10%,and the effective measurement range of the capacitance sensor was obtained for the gas content rate in the range of 10% to 70%,and the capacitance value of the gas content rate from 10% to 70% was fitted,and the maximum deviation value between the measured capacitance value and the fitted theoretical capacitance value was obtained as the maximum deviation between the measured capacitance value and the fitted theoretical capacitance value is 0.00209 pf,and the stability of the measurement performance of the sensor is tested by repeating the test.The maximum absolute errors are about: 40%,0.40%,0.17%,0.14%,0.31%,0.27%,0.22%,which indicate that the array capacitance sensor can maintain good measurement capability under repeated measurements.