Flow Characteristics Measurement Of Churn Flow In Oil-Water-Gas Three-Phase Flow Using Wire-Mesh Sensor

Oil-water-gas three-phase flow widely exists in petroleum,chemical and other important industrial production processes.The accurate measurement of flow structures and parameters is of great significance for uncovering fluid dynamics behavior and optimizing industrial production processes.Compared with gas-water or oil-water twophase flow,the flow structures of oil-water-gas three-phase flow are more complex due to the physical property differences of the three phases and the interaction between phases.Churn flow is one of the common flow patterns in oil-water-gas three-phase flows.Two non-conductive dispersed phases(oil droplets and gas bubbles)in churn flow lead to great challenges in measuring the gas holdup.In this thesis,a conductivity Wire-Mesh sensor(WMS)system based on FPGA is developed to detect the vertical upward oil-water-gas three-phase churn flow.A combined measurement system of WMS and distributed coaxial conductance sensor(DCCS)is established to realize the correction of WMS visualizations,and a new method of three-phase flow gas holdup measurement based on single-modality sensor is proposed.The structure characteristics and the evolution of churn flow in vertical upward gas-water flow and oil-water-gas flow are studied.The transition boundary between slug flow and churn flow is predicted by establishing physical models.The innovative research achievements of this thesis are as follows:1.COMSOL software is used to simulate the electric field distribution of the WMS,and the dynamic responses of the WMS to multi-scale and non-uniform bubbles are studied.The formation mechanism of over range and cross talk phenomenon in the measurement response is revealed.The conductivity WMS system based on FPGA is independently developed,which can effectively improve the measurement capability to the small-scale bubbles.At the same time,the hardware system architecture is optimized to improve the integration and rapidity of the measurement system.By conducting calibration experiments,it is found that the developed WMS system has good response characteristics to stratified flow and dispersed flow.2.A combined measurement system of WMS and DCCS is established.This system can visualize the flow structure in three-phase flow,and provides a new idea for parameter measurement of multi-phase flow by using single-modality sensor.The flow structures and evolution characteristics of churn flow in two-phase flow and three-phase flow have been comparatively studied.Based on the WMS flow visualizations,the gas holdup of oil-water-gas three-phase flow is extracted,and the influence of the oil phase on the local structures and the average gas holdup has been studied.3.The physical mechanism of the gas-water slug-to-churn flow transition is investigated,and a flooding model and an aerating model are established.The adaptability of different physical models under the gas-water two-phase flow conditions is investigated.According to the special flow structures of oil-water-gas three-phase flow,the flooding model and the aerating model are modified.The slug-to-churn flow conversion boundaries predicted by different modified models are compared with the experimental flow pattern map.It is found that the flooding model taking the length of liquid film and its fluctuation characteristics into account has obvious advantages in predicting the flow pattern transition.