Electrical Impedance Sensors for Multi-Phase Flow Measurement: A Review

The impedance flow sensors have usually been considered as the competitive components in the multi-flow measurement, primarily due to their advantages of fast response, high dynamic range and sensitivity, non-invasive and/or non-intrusive measurements. In this review, the impedance sensors have been categorized into two categories, i.e., the probes for local/average parameter measurement and sensor arrays for distributed parameter measurement. Maxwell's equations and boundary conditions have been referred as a starting point to understand the measuring principle of impedance sensors, from which the sensitivity distribution can be attained. The sensitivity distribution can be utilized to characterize the sensor and employed as an objective function in optimizing the sensor geometry. The EMA models usually offer a way to relate the impedance measurements to individual phase fraction, which have been critically reviewed. In addition, the application range, spatial and temporal resolutions, advantages and disadvantages of the sensor arrays, i.e., the wire mesh sensor, field focusing sensor, electrical resistance and capacitance tomography sensors have also been provided. Finally, the future trends of impedance sensor development have been briefly discussed.