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Two tomographic techniques have been applied simultaneously to the flow of air and silicone oil in 67 mm internal diameter vertical pipe. A twin plane electrical capacitance tomgraphy (ECT) electrode system driven by Tomoflow electronics was positioned below a new capacitance wire mesh sensor (WMS) system. The former used 8 electrodes around the pipe in each plane, the latter employed two arrays of 24 evenly spaced wires stretched over the pipe cross-section. The ECT measurement was triggered from the WMS electronics. High speed videos were also taken simultaneously through the transparent pipe wall. Gas superficial velocities of 0.05-5.5 m/s and liquid superficial velocities of 0-0.7 m/s were studied. These gave bubbly, slug, and churn flow in the pipe. The outputs of the two techniques have been compared at a number of levels. At its most basic, the time averaged cross-sectionally averaged void fractions were compared. They showed excellent agreement. At the next level, the time series of the cross-sectionally averaged void fraction were considered directly and through their variations in amplitude and frequency space. Examples of probability density functions are presented. Radial variations of the void fraction were also considered. Thereafter the shapes of the large bubbles and the velocities of periodic structures are presented.

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This work reports the effects of the presence of a gas or vapor phase on mechanically agitated liquid mixing. A conductivity technique was used to follow the assimilation of tracer added at the liquid surface of cool aerated, hot sparged, and unsparged boiling liquid. The 75-L-capacity baffled vessel had a single, centrally mounted, Chemineer CD-6 hollow blade impeller. Sparging increases the rate of mixing at a given shaft power, especially at high gas flow rates. Inconsistencies in the literature on the effect of aeration on the mixing time are satisfactorily resolved if the potential energy input from gas sparging is considered. When this is done, hot and cold sparged and unsparged mixing times are comparable, provided that the contribution of the volume of any vapor generated is included. Mixing of surface added tracer into boiling liquid is considerably faster at a given impeller power than in any of the other conditions. This is probably a result of the additional disturbance at the liquid surface produced by vapor evolution causing a rapid initial distribution of tracer.