Imaging stratifying liquid–liquid flow by capacitance tomography

Abstract

Electrical capacitance tomography offers a non-intrusive technique for on-line visualisation of two-phase liquid–liquid flows. It has been applied on a facility which provides metered flows of water and kerosene to a test section at the start of which they pass through a dispersing multi-hole orifice plate. The test section consists of a sudden expansion with an internal diameter of 63 mm inlet and 100 mm outlet and which can be inclined. Beyond this the mixture is separated into the two constituents and returned to their individual tanks. Tomography measurements were made using a PTL-300 electronic system coupled to a 12-electrode sensor which was built in-house. The sensor is fitted on the outside of one of the plastic pipe lengths of the test section. By varying the input oil fractions from 20% to 70%, using mixture velocities of 0.2, 0.3, and 0.4 m/s and positioning the pipe at angles of +6 ∘,+3 ∘,0 ∘, −4 ∘ and −7 ∘ to the horizontal, different flow patterns were established in the test section. A specially developed calibration method is used in all experiments and tomographic images of the stratifying liquid–liquid flow were obtained. These images show clearly that the spatial distribution in a pipe cross-section is strongly dependent on the mixture velocity and the distance from expansion in the range studied. Concave interfaces were observed in horizontal and downward inclination flow for all cases while convex interfaces were identified only in an upward inclination flow at the high input oil fractions and high mixture velocities. This application illustrates very clearly the capability of the ECT for on-line imaging of liquid–liquid two-phase flows.