The Measurement Characteristics Of Coaxial Fluid Capacitance Sensor Used In Oil-water Two-phase Flow

Two-phase flow phenomenon exists widely in petroleum, energy, pharmaceuticaland chemical industry process. The phase volume fraction and individual phasevelocity are important factors to reflect the dynamic characteristics of two-phase flow.However, due to the slippage phenomenon, the local concentration and velocitydistribution are complex, which results in difficulty for phase volume fractionmeasurement. This paper focuses on the research for the measurement characteristicsof coaxial fluid capacitance sensor used in oil-water two-phase flow volume fractionmeasurement, through optimum designing the sensor, we study its measurementcharacteristics in two-phase flow loop test facility, the innovative research results areobtained as follows:1. By using finite element method (FEM), we investigate the affect of thedifferent structure parameters on the distribution characteristic of the electric field andthe sensitivity field of coaxial capacitance fluid sensor, and then figure out theoptimum sensor geometry based on the optimal sensitivity principle. Additionally,through the investigation of the affect of oil bubble size on the sensor responsecharacteristics, we get the theoretical basis for analyzing its measurementcharacteristics.2. We design the coaxial fluid capacitance sensor and measurement circuit baseon its geometry optimization. Combined with PXI data acquisition module, we buildthe sensor measurement system. We carry out the dynamic experiment using thecoaxial fluid capacitance sensor at the flow condition in which the water-cut is from0%to100%and flow rate from0.5m3/d to7m3/d, The experimental resultsshow that the sensor has high resolution for measuring the water volume faction.3. Based on the transient fluctuating signals measured by the sensor, we extractthe water holdup value and establish the drift-flux model, the results show that thedispersed phase velocity can be well predicted with the model. In addition, we alsoinvestigate the time-frequency distribution characteristics of different flow patternsbased on the fluctuating signal, and we find that the five typical different oil-watertwo-phase flow patterns can be well distinguished through the joint total energy anddominant frequency distribution characteristics.