Calibration of capacitance tomography systems for liquid-liquid dispersions

Electrical capacitance tomography (ECT) provides information on the flow regime and concentration distribution in process vessels and pipelines containing two-phase mixtures. This is achieved by arranging sensors around the pipe or vessel to be imaged. The sensor output signals depend on the position of the phases within the sensing zone. A computer is then used to reconstruct an image of the pipe cross section from the sensor measurements. It is necessary to calibrate the ECT system by filling the sensing zone consecutively with the low permittivity material, then the high permittivity material. When the high permittivity material is introduced into a low permittivity background within the sensing zone, the capacitance between sensors will increase. This paper demonstrates that this calibration procedure coupled with the existing image reconstruction software is inappropriate for imaging liquid-liquid dispersions containing low fractions (below 0.3) of water in kerosene. An alternative calibration procedure is proposed which yields substantially improved images.