The Measurement Characteristics Of Parallel-Wre Capacitance Sensor Used In Two-Pase Flow

Two phase flow widely exists in many industry fields, such as the oil industry, the energy industry, the pharmaceutical process and daily chemical industry, etc. In the production process, the parameters such as the phase holdup and flow rate are of great importance for the measurement, control and reliable operation of the industrial process. Since the two-phase flow is a complex nonlinear system and its flow structures to be highly random, not stability and polymorphism, it is very difficult to accurately measure the process parameters. The measurement objects of this research are oil-water and gas-liquid two-phase flow in a small diameter pipe. The research object is the measurement of section phase holdup. Optimizing the probe geometry parameters and design the measurement system are mainly investigated.Firstly, based on the existing knowledge about the design of capacitance sensor, we develop a parallel-wire capacitance sensor to measure the water holdup. Considering the advantage of finite element method in the analysis of the electrostatic field, we use finite element method and computer-aided design to optimize the parameters of sensor structure. Based on the optimization indexes, e.g., the relative sensitivity and uniformity, we conduct two-dimensional optimization simulation for the geometry structure parameters of capacitance probe. The effect of the sensor geometry parameters on the sensitivity field has been investigated. Different structural parameters of the sensor for the oil-water stratified flow will result in different linearity of their response. Based on the above operations, we can obtain an optimized sensor.Secondly, in the design of the capacitance detection circuit, the AC excitation method is used. According to the simulation results, we design a longitudinal array of the parallel-wire capacitance sensor. The response of this sensor for oil-water stratified flow static experiments indicates the senor presents high sensitivity and good linearity; The response of this sensor for vertical gas-liquid dynamic experiments indicates the senor have high sensitivity for different section water holdup.Finally, the parallel-wire capacitance sensor’s signals can reflect the global characteristics of vertical gas-liquid flow patterns. The mixture velocity is calculated by the cross-correlation flow measurement technique. The result shows that the parallel wire capacitance sensor have the better total flow measurement characteristics. In addition, we using the method of multi-scale fractal study the multi-fractal properties of signals measured from vertical gas-liquid two-phase flow. We also calculate the Hurst exponent of different scale signal of gas-liquid two-phase flow patterns and investigate the long-range correlation and dynamic mechanism of gas-liquid two-phase flow. The dynamic characters of different flow patterns in different frequencies were clearly described by the multi-scale analysis applied to the capacitance fluctuate signals, and it was a powerful tool to characterize the dynamic movement of two-phase flow from scale to micro scale.