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Gamma-densitometry tomography (GDT) experiments have been performed to measure gas holdup spatial variations in two bubble columns: a 0.19 m inside diameter Lucite column and a 0.48 m inside diameter stainless steel vessel. Air and water were used for the measurements. Horizontal scans at one vertical position in each column were made for several air flow rates. An axisymmetric tomographic reconstruction algorithm based on the Abel transform has been used to calculate the time averaged gas holdup radial variation. Integration of these profiles over the column cross section has yielded area-averaged gas holdup results, which have been compared with volume-averaged gas holdups determined from differential pressure measurements and from the rise in the aidwater interface during gas flow. The results agree reasonably well. INTRODUCTIONBubble-column reactors are used extensively by chemical manufacturers to perform a wide variety of gas/liquid or gas/liquid/solid reactions such as oxidation, hydrogenation, chlorination, aerobic fermentation and coal liquefaction (Shah and Deckwer, 1983). Bubble-column reactors are generally tall, cylindrical vessels filled with liquid, sometimes laden with a solid catalyst, c through which a gas is injected using a sparger at or near the bottom. The gas reacts with the liquid or catalyst to form a desired product, either a gas or a liquid, that is continuously removed from the vessel. Pressures and temperatures are controlled during the reaction to optimize product distribution. One of the main benefits of slurry-phase bubble-column reactors used in catalytic reactions is the ability of the liquid phase to provide an efficient heat sink for highly exothermic reactions. Under industrial conditions, the pressure, temperature, inlet gas velocity, and column diameter may be increased, to maximize total product production rates. The effects of increasing these parameters on the multiphase flow phenomenology must be considered when attempting to scale laboratory reactors to industrial sizes and operating conditions. Development and application of noninvasive tomographic diagnostics capable of measuring gas holdup (ratio of local gas volume to total volume) spatial distributions in full-scale reactors will greatly facilitate current efforts to predict reactor performance.Gamma densitometry has been applied for measurement of local density in multiphase flows for some time (e.g., Petrick and Swanson, 1958;Swift et al., 1978;Chan and Banerjee, 1981).Standard gamma densitometry measures gamma attenuation integrated along a path through the medium, and thus lacks spatial resolution. However, spatially resolved measurements can be made by applying tomographic reconstruction algorithms to the results of measurements along many different paths. Although gamma-densitometry tomography (GDT) can measure spatially resolved gas holdup in a gas/liquid flow, neither instantaneous gas holdup nor bubble size distributions can be measured due to the time required for data acquisition. Several groups...

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