Fast imaging of the velocity profile of the conducting continuous phase in multiphase flows using an electromagnetic flowmeter

Abstract

This paper describes a novel dual-frequency inductive flow tomography (IFT) system, which relies on the use of a multi-electrode electromagnetic flow meter (EMFM). This flow meter is currently capable of imaging the velocity profile of the conducting continuous phase of both single phase and highly asymmetric multiphase flows ten times every second. Uniform and anti-Helmholtz magnetic fields are simultaneously applied to the cross section of the flow tube of the EMFM. This enables flow induced potentials to be measured, at an array of electrodes, flush mounted on the inner wall of the EMFM, ten times every second using a multi-channel analogue signal conditioning system. These measured flow induced potentials are then used in an image reconstruction algorithm to reconstruct the water velocity profile in the flow cross section at 0.1 s time intervals.A series of experiments were carried out in water continuous, upward, air-water flows inclined at 15° to the vertical to measure the water velocity profile using the IFT system. The water velocity profiles were compared with air velocity profiles previously obtained for inclined air-water flows at similar flow conditions using local probing techniques. For all of the flow conditions investigated it was found that both the local axial water and air velocities were significantly greater at the upper side of the inclined pipe than at the lower side. The high local water velocities were probably due to upward momentum of the air bubbles being locally transferred to the water at the upper side of the inclined pipe. A comparison of the local axial air velocity distribution and the local axial water velocity distribution also showed that the local slip velocity between the phases varied markedly in the flow cross section – indicating that previous assumptions that the local slip velocity is constant in the flow cross section are clearly incorrect.