Mechanism Of Conductive/electromagnetic Sensor Used For Two-Phase Flow Measurement

Two-phase flow widely exists in nature and industrial process. Accurate measurement of two-phase flow parameters is of great importance to the national economic development. However, two-phase flow is pretty complicated as there is variable interface and relative movement between phases. Thus, precise measurement of two-phase flow parameters has always been a burning issue in scientific research and industrial application. Based on two-phase flow mechanism and basic measurement technique, a novel method which combines conductance sensor and electromagnetic sensor is proposed in this paper for volume fraction and velocity measurement. The architecture and associated fundamental theory of the new presented method is analyzed for multi-parameter measurement. The main contents of the paper are as follows:1. The electric field is sensitive to pipe flow distribution. Finite element numerical method has been adopted to study the electric field of the conductance sensor. The effect of the concave-shaped electrode angle on the electric field distribution is discussed according to the uniformity concept. Electric field sensitivity under various electrode axial lengths and relating information has also been studied. The construction parameters of optimized conductance sensor are then identified.2. In the research of electromagnetic sensor, saddle coils are excited to generate uniform magnetic field while the concave-shaped electrodes in conductance sensor are applied to measure the induced voltage. Weight function of electromagnetic sensor with concave-shaped electrodes is computed and compared with the finite element numerical simulation. The result shows that the weight function distribution is more uniform than the point electrodes one. The behavior of the electromagnetic sensor under different velocity profiles verifies the feasibility of the electromagnetic sensor to be employed in two-phase flow measurements. The magnetic field characteristic of saddle coils is studied and the coils parameters are identified to generate uniform magnetic field in the measuring area.3. For gas-liquid two-phase flow parameters measurement, measuring system with conductance/electromagnetic sensor is designed and time-sharing operating mode is applied. When the conductance sensor is operated to measure the volume fraction, excitation in saddle coils is disabled and concave-shaped electrodes are used as exciting and measuring electrodes. When electromagnetic sensor is adopted to measure the volume velocity, excitation in saddle coils is exerted and concave-shaped electrodes are used to measure the induced voltage.4. Experiments are carried out to verify the measuring mechanism of conductance/electromagnetic sensor. It is indicated that measured conductance value of the conductance sensor is linearly changed with the variation of medium conductivity which is in accordance with theory. Also, the liquid fraction of gas-liquid annular, bubble and slug flow can be predicted by dimensionless voltage measured by the conductance sensor. The response of electromagnetic sensor to axisymmetric and non-axisymmetric velocity distribution shows that the sensor with concave-shaped electrodes is less sensitive to flow profiles and can be considered to measure two-phase flow parameters.