A Capacitance Sensor for Gas/Oil Two-Phase Flow Measurement: Exciting Frequency Analysis and Static Experiment

A capacitance sensor with high sensitivity was applied to oil-gas two-phase measurement based on a modeling and experimental studies. A model of the electric behavior of the material system between electrodes, comprising fluids and pipe, was developed to choose the optimum working frequency using two types of electrode configurations: double ring and concave, which differ in terms of linearity of response, sensitivity, and phase distribution dependence. According to the model, medium frequencies, 800-1000 KHz, is the best choice for gas-oil ratio measurement. Subsequently, a capacitance sensor was designed and constructed using electrodes mounted at the outside of the wall of a polyester tube in a static test bench to measuring gas-oil ratio. The model and experimental results show better sensitivity of ring configuration, whereas concave one presented better linearity of response. Moreover, ring configuration is less affected by air/oil distribution, although both electrodes showed dependence on flow pattern. The experimental results confirm reducing in sensitivity of both electrodes by increasing the frequency. The gas-oil ratio was determined directly from the output voltage changes instead of measuring the capacitance as void fraction indicator.