Spatial resolution improvement of EIT system using internal invasive electrodes for measurement of two-phase flow
Hirose, Yoshiyasu ; Kukita, Yutaka; Shibamoto, Yasuteru ; Sagawa, Jun*
Electric impedance tomography (EIT) is a non-invasive and radiation-free imaging method applicable to gas/liquid two-phase flow measurements. It determines the electrical resistivity distribution of an object from measurements of boundary potentials in response to current injection. Due to the severely ill posed nature of the problem, the quality of reconstructed image depends much on the quality and amount of information available from potential measurements. We have proposed a DC pulse-driven EIT system design equipped with countermeasures for the influences of electrode polarization on potential measurements (Hirose et al., in preparation). The usefulness of EIT in two-phase flow measurement is however restricted by the intrinsically limited spatial resolution. Due to the diffusive nature of electricity, the spatial resolution degrades quickly with the distance from the boundary. In this study, we attempt to improve the spatial resolution by adding thin electrodes inserted into the flow field away from the boundary. Although this means that non-invasiveness is traded off, the influence of invasive electrodes on flow field could be estimated and limited on the basis of experiences gained with other intrusive methods, e.g., needle probes for measurement of interfacial area. The benefit taken by the addition of invasive electrodes, on the other hand, would depend on two-phase flow regime and other flow parameters. In the present paper we consider dispersed bubbly flow and simulate the bubbles with thin cylindrical insulators. The results obtained with and without invasive electrodes are compared to discuss the effectiveness and limitations in measurement of two-phase flow.