Concave Capacitance Research Articles

Complex Admittance Detection of Horizontal Oil-Water Two-Phase Flows Using a Capacitance Sensor

Capacitance sensors have been widely used in the measurement of two-phase flows encountered in industrial processes due to their advantages of non-intrusiveness and quick response. In this paper, an equivalent circuit model of a concave capacitance sensor for stratified oil-water flow is established. Based on this model, the effects of the excitation signal frequency on the fluid admittance are investigated to optimize the geometric structure of the concave capacitance sensor. A capacitance sensor system is designed to simultaneously detect the real (Re) and the imaginary (Im) parts of the oil-water complex admittance. The Re and Im response signals of the capacitance sensor are collected in the dynamic experiment of horizontal oil-water flows. The influences of the flow pattern and the excitation frequency on the measurement of fluid complex admittance are experimentally explored.

Instability of horizontal oil-water flows based on the signal-dependent complex admittance representations

Horizontal oil-water two-phase flows are characterized by unstable motions of interfacial wave and entrained droplets. An experiment of horizontal oil-water flow was made in an acrylic pipe with an inner diameter of 20 mm. A measurement system of concave capacitance sensor is designed to detect the real and imaginary parts of flow complex admittance. An Adaptive Optimal Kernel Time-Frequency Representation (AOK TFR) of the complex admittance angle is used to characterize the flow instability in terms of total energy. A detrended cross-correlation analysis (DCCA) of the oil-water complex admittance is conducted to investigate the instability multi-scale flow structures. The cross-correlation coefficients at large and small scales enable to characterize the instability of the oil-water interface and the entrained droplets in continuous phases, respectively. The result suggests that the DCCA cross-correlation coefficients and the total energy extracted from AOK TFR are accordant in uncovering the instability of horizontal oil-water flows.

Capacitive Phase Shift Detection for Measuring Water Holdup in Horizontal Oil⁻Water Two-Phase Flow.

In this paper, a phase shift detection system of flow impedance is designed based on a concave capacitance sensor (CCS). The flow impedance of oil–water stratified flow is investigated by establishing an equivalent circuit model and a finite element model. The influence of exciting frequency and sensor geometric parameters on the phase shift output of the CCS is studied to access an optimal phase shift measurement system. An experiment of horizontal oil–water two-phase flows was conducted during which four flow patterns are observed, i.e., stratified flow (ST), stratified wavy flow (SW), dual continuous flow (DC), and dispersed oil-in-water and water flow (DO/W&W). The phase shift responses of the CCS to the water holdup variation are collected. The results indicate that the phase shift response of the CCS presents satisfied sensitivity for ST and SW flow patterns, which is consistent with the predictions of the equivalent circuit model and the finite element model. Although the flow structures of DC and DO/W&W flows are extremely nonuniform, the phase shift response of the CCS still shows better linearity and sensitivity to the water holdup variation. In general, the capacitive phase shift detection technology exhibits advantages for water holdup measurement in horizontal oil–water two-phase flow with nonuniform phase distributions and conductive water.

Void fraction measurement using concave capacitor based sensor – Analytical and experimental evaluation

Two-phase flow in pipelines is very common in the oil and gas industries. Void fraction is one of the important parameters in two-phase flow. Measurement of void fraction plays an important role in various areas of industries. Two types of measurement techniques are commonly used in electrical methods for macroscale range- variable capacitance type and variable conductance type. A comparatively low cost and non-invasive design of the concave capacitive sensor is analytically evaluated and experimentally validated to measure the void fraction inside the non-metallic pipe. The design is effective to reduce the fringing effect. The electrical model of the concave capacitance sensor is analyzed, which involves all the parasitic capacitances along with the cable capacitances. The capacitance of the sensor varies for the whole range of void fraction (0–100%). If the two phases are distilled water and air, the capacitance value varies from 94.0134 pF to 3.4377 pF experimentally for void fraction variation of 0–100%. Uncertainty analysis for the proposed sensor design along with the uncertainty budget is presented, for the whole range of measurement. The standard uncertainty is less than 0.97 pF for the whole range of measurement. The procedure for analysis is also discussed in this paper.

Different configurations of capacitance sensor for gas/oil two phase flow measurement: An experimental and numerical study

In this paper, an experimental investigation and numerical study were performed on different electrode configurations for oil-air two phase flow measurement in different patterns. The main electrode configurations are: double ring, concave and double helix that can be compared in terms of sensitivity and phase distribution immunity. For this purpose, finite element simulations were carried out to compare electrode configurations as well as experimental study. Also a new electrode shape (TRFLC) was proposed and compared with the others. The simulation results show different sensitivity for each flow pattern: for stratified regime, TRFLC and for annular regime, concave and helical shapes were more sensitive. Concave shape was strongly dependent on the flow pattern while helical and ring show less dependency. Then, an experimental set up was constructed for oil-air two phase flow in a 26.6 ID horizontal pipe. Also, a capacitance sensor with high sensitivity was designed, using those electrode configurations, to measure small changes in the capacitance values of oil-air two phase flow and converting to voltage by a transducer circuit. The sensor responses for each configuration show TRFLC and concave had the most overall sensitivity for the pipe filled with oil and air which is consistent with the results of simulation. Flow pattern detection with the concave capacitance was clearly possible without the need for signal processing, regimes such as bubbly, slug, plug and wavy, and gas-oil ratio was obtained using helical type with an absolute percentage error less than 8%. In summary, if the main objective is identification of flow regime, then the TRFLC or concave shape is preferred and on the other hand, helical shape is favored if measurement of gas fraction is the target.

An on-line adaptive estimation method for water holdup measurement in oil–water two-phase flow with a conductance/capacitance sensor

Oil–water two-phase flow widely exists in industrial processes such as petroleum engineering and chemical engineering. Accurate and real-time measurement of water holdup is an important problem requiring urgent solutions. In this work, a conductance and capacitance combination sensor (CCCS) system with four conductance rings and two concave capacitance plates was validated for its measurement performance of in situ water holdup through dynamic experiments. An online adaptive weight Kalman estimation (OAWKE) fusion algorithm for the CCCS system is proposed to fuse the conductance measurement and capacitance measurement. The algorithm has fast and dynamic response for the water holdup measurement of oil–water two-phase flow and has improved measurement precision by the adaptive data fusion method. The OAWKE fusion algorithm also has the ability to deal with the abrupt change of water holdup during the measurement process. Therefore, in the low water conductivity condition (tap water), the CCCS system with the OAWKE fusion algorithm can dynamically estimate the real-time full range water holdup of oil–water two-phase flow, which has prospects in the petroleum industry.

Design of a Conductance and Capacitance Combination Sensor for water holdup measurement in oil–water two-phase flow

Oil–water two-phase flow widely exists in the process of petroleum industry. The liquid holdup measurement in horizontal pipeline is very important and difficult. In this work, a Conductance and Capacitance Combination Sensor (CCCS) system with four conductance rings and two concave capacitance plates is designed and validated for its measurement performance of in situ water holdup through dynamic experiments. A set of fast electronic switches controls the conductance rings and the capacitance plates alternatively set up each own sensing field in the same sensing volume. This configuration ensures the water holdup estimation in the range from 0% to 100% regardless of flow direction. A set of quick closing valves was used to acquire the in situ holdup for the on-line calibration of the CCCS system. The theoretical correlations of conductance sensor and capacitance sensor were established to make the real-time measurement convenient. A real-time measurement method by CCCS system is provided based on the fusion of the conductance and the capacitance measurement without flow pattern recognition. This method delivers an average error of 1.06% for the CCCS system measuring the water holdup of oil–water two-phase flow, with a standard deviation of 0.038 and a relative error less than ±5%.

Liquid holdup measurement in horizontal oil–water two-phase flow by using concave capacitance sensor

Due to the complex flow structures of horizontal oil–water flows, the liquid holdup measurement is still a challenging problem. In this paper, we using the finite element analysis build a two-dimensional model of the concave capacitance sensor and investigate the effect of sensor geometry on the distribution of the sensitivity field. Through calculating the sensor static response for different horizontal oil–water flow patterns, we figure out the optimum geometry of the concave capacitance sensor. In addition, we conduct experiment to obtain the measured response of the concave capacitance sensor and achieve the oil-holdup by using quick closing valve. The results indicate that the optimized concave capacitance sensor shows good performance for liquid holdup measurement of horizontal oil–water two-phase flow.

Determination of the theoretical capacitance of a concave capacitance sensor

The practical use of four concave capacitance plates for determining in situ volume fractions in two-phase pipelines has been amply demonstrated. In this letter, the system is analyzed theoretically using a microstrip technique and the results are compared with experimental data.