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An implementation of resistive electrical-impedance tomography (EIT) for measuring material distributions of multiphase flows in vessels with electrically conducting walls is presented. Seven ring electrodes are equally spaced on a thin nonconducting rod that is inserted into the vessel. The vessel wall is grounded and serves as the ground electrode. Voltage distribution measurements are used to numerically reconstruct the time-averaged impedance distribution within the vessel, from which the material distributions are inferred. Experimental results for the case in which the rod is inserted coaxially into a liquid-filled vertical standpipe containing beds of different heights of nonconducting solid particles are presented. Agreement between the direct measurement and the numerical reconstruction of the particle-bed height is good. Application of this technique to a pilot-scale slurry bubble-column reactor is discussed.

A novel electrical-impedance tomography (EIT) diagnostic system, including hardware and software, has been developed and used to quantitatively measure material distributions in multiphase flows within electrically-conducting (i.e., industrially relevant or metal) vessels. The EIT system consists of energizing and measuring electronics and seven ring electrodes, which are equally spaced on a thin nonconducting rod that is inserted into the vessel. The vessel wall is grounded and serves as the ground electrode. Voltage-distribution measurements are used to numerically reconstruct the time-averaged impedance distribution within the vessel, from which the material distributions are inferred. Initial proof-of-concept and calibration was completed using a stationary solid-liquid mixture in a steel bench-top standpipe. The EIT system was then deployed in Sandia's pilot-scale slurry bubble-column reactor (SBCR) to measure material distributions of gas-liquid two-phase flows over a range of column pressures and superficial gas flow rates. These two-phase quantitative measurements were validated against an established 3 gamma-densitometry tomography (GDT) diagnostic system, demonstrating agreement to within 0.05 volume fraction for most cases, with a maximum difference of 0.15 volume fraction. Next, the EIT system was combined with the GDT system to measure material distributions of gasliquid-solid three-phase flows in Sandia's SBCR for two different solids loadings. Accuracy for the three-phase flow measurements is estimated to be within 0.15 volume fraction. The stability of the energizing electronics, the effect of the rod on the surrounding flow field, and the unsteadiness of the liquid temperature all degrade measurement accuracy and need to be explored further. This work demonstrates that EIT may be used to perform quantitative measurements of material distributions in multiphase flows in metal vessels.

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The effect of structural modulation of porous-layer coating on the qCHF for horizontal surfaces is examined experimentally. The surface consists of a copper substrate coated with spherical copper particles which are diffusion sintered into modulated structures inside graphite molds. Results are reported for pentane boiling on four different surfaces; a plain uncoated surface, a surface with a porous-layer coating of uniform thickness, and two surfaces with different modulated porous-layer coatings. A two-fold increase in the critical heat flux (qCHF) is found for one of the modulated porous-layer coatings. A brief explanation of the hydrodynamic theory for the qCHF is then given in which it is postulated that the qCHF occurs when columnar, vapor-escape passages through the liquid become unstable and collapse. It is then hypothesized that the enhancement of the modulated coating results from surface-induced changes in the characteristic interfacial wavelengths that stabilize the liquid-vapor interfaces, delaying the collapse of these vapor escape paths, and ultimately increasing qCHF.