A highly adaptive electrical impedance sensing system for flow measurement

As a generic 'tool' electrical impedance tomography (EIT) is useful in improving the modelling and design of many complex processes and for process control (Williams R A and Beck M S 1995 Process Tomography: Principles, Techniques and Applications (Woburn, MA: Butterworth Heinemann) pp 11-25, Neuffer D, Alvarez A, Owens D H, Ostrowski K L, Luke S P and Williams R A 1999 Proc. 1st World Congr on Industrial Process Tomography (Buxton, UK) pp 71-7). However, existing developments of the EIT technique are only applicable to aqueous-based fluids that possess continuous admittance property (Xie C G, Reinecke N, Beck M S, Mewes D and Williams R A 1994 Process Tomography-A Strategy for Industrial Exploitation ed M S Beck pp 25-32). For example, it would not be suitable for a stratified flow or an intermittent flow in a horizontal channel or large bubble formation and foams since some of the electrodes may lose contact with the conductive fluid. The paper reports a preliminary study of a novel sensor and apparatus, which seeks to address some significant shortcomings in EIT application through use of a new sensing strategy and apparatus for measuring complex multiphase flows, such as oil/gas/water flow or bubble formation and foams. The major feature of the sensing system is to employ a single conductive ring as a tomographic sensor instead of a number of electrodes as in conventional EIT. The strategy facilitates a more homogeneous sensitivity distribution throughout the sensing domain of the conductive ring, which is less affected by the contact area or geometry of electrodes than in previous EIT systems. The sensor can be conveniently constructed as a flange-based flow sensor, if required, without the need to drill holes in the pipe wall. Therefore, it provides a realistic way to measure the dynamic changes of flowing fluids. The novel methodology is believed to offer a significant advance in enabling a more flexible and robust EIT system to be devised for on-line measurement and control of flow in oil, pharmaceuticals and food industries.