Toward Electrical Capacitance Tomography of Water-Dominated Multiphase Vertical Flows

Imaging of multiphase flows holding water as continuous phase (i.e., water-dominated flows) is very challenging for conventional electrical capacitance tomography (ECT) due to the high permittivity of water. In this paper, we introduce a new approach, based on the multi-frequency excitation of ECT sensors, for imaging and real-time monitoring of water-dominated columnar or slug vertical flows. The proposed method exploits differences between measurements obtained at distinct frequencies caused by the Maxwell-Wagner-Sillars effect, which is present in multiphase flows with at least one conducting phase. To illustrate this new approach, several numerical simulations are carried out for two-phase and three-phase mixtures containing air, methylamine, and/or oil as dispersed phases and with water as the continuous phase. Experimental results are also provided to validate the findings.

I. Introduction

Electrical Capacitance Tomography (ECT) is a popular soft-field tomography technique for imaging and real-time monitoring of flow processes. ECT is widely employed to monitor multiphase flows involving gas, oil, and other low permittivity materials in packed bed reactors, trickle bed reactors, and other industrial settings [1]–[16]. Due to their relatively low energy consumption and robustness, packed bed reactors are highly suitable, for example, for space applications [17] such as water filtration [18] and waste water treatment in microgravity environments. However, water-dominated flow imaging has remained a challenge for conventional ECT due to the high permittivity of water [19]–[22]. In the past, Jaworski and Bolton [19] developed an technique to image flow patterns holding water. This approach was predicated on the use of internal electrodes in direct contact with the sensed media, which in many industrial settings cases is impractical. Hasan and Azzopardi have presented a method to image flow patterns of water and other phases, but limited to stratified horizontal flow patterns [23].