An Impedance Cross Correlation (ICC) device for measuring solids velocity and volume fraction profiles in solids-water flows

Abstract

Multiphase flow is the simultaneous flow of two or more phases, in direct contact, in a given system. It is important in many fields of chemical and process engineering and in the oil industry, e.g. in production wells and in sub-sea pipelines. The behavior of the flow will depend on the properties of the constituents, the flows and the geometry of the system. Upward inclined solids-liquid flows are sometimes encountered in the process industries for example in water treatment processes and in oil well drilling operations. Measurements of the local solids volume fraction distribution and the local axial solid velocity distribution are important, for example, in measuring the solids volumetric flow rate. This paper presents a non-intrusive Impedance Cross-Correlation (ICC) device to measure the local solids volume fraction distribution and the local axial solids velocity distribution in upward inclined solids-water flows in which these distributions are highly non-uniform. The ICC device comprises a non-conductive pipe section of 80mm internal diameter fitted with two arrays of electrodes at planes, A and B, separated by an axial distance of 50mm. At each plane, eight electrodes are equispaced over the internal circumference of the pipe. A control system consisting of a microcontroller and analogue switches is used such that, for planes A and B, any of the eight electrodes can be configured as an ‘excitation electrode’ (V+), a ‘virtual earth measurement electrode’ (ve) or an ‘earth electrode’ (E) so that different regions of the flow cross section can be interrogated. Conductance signals from planes A and B are then cross correlated to yield the solids velocity in the region of flow under interrogation. Experiments were carried out in water-solids flows in a flow loop with an 80 mm inner diameter, 1.68m long Perspex test section which was inclined at o 30 to the vertical. The most significant experimental result is that, at the upper side of the inclined pipe, the measured solids velocity is positive (i.e. in the upward direction), whilst at the lower side of the inclined pipe the measured local axial solids velocity is negative (i.e. in the downward direction). This shows quantitative agreement with previous work carried out using intrusive local probes to measure the solids velocity profile. The study also shows qualitative agreement with high speed film of the flow. It is believed that this method of velocity profile measurement is much simpler to implement than dual-plane electrical resistance tomography (ERT)