A compact optical fiber probe to measure the velocity of solid particles in twophase flows was constructed. The probe has been used to measure particle velocities and obtain flow trajectories of solids in the distributor grid region of a two-dimensional fluidized bed. Air was used as the fluidizing medium in a bed of glass beads of size ranging from 0.2 to 0.7 mm.Particle velocities were measured at corresponding points within a jet in the twodimensional bed, using the optical fiber probe and a Laser Doppler Velocimeter (LDV). The probe measurements compare well with the LDV results in the main jet region. Particle velocities were also measured with the probe in the dense phase region of the fluidized bed where measurements were not possible using LDV. The resulting flow maps clearly indicate solids circulation patterns around jets and identify dead zones formed on the distributor plate. B. PATROSE and H. S. CARAM Department of Chemical EngineeringLehigh University Bethlehem, PA 18015 SCOPEIntense mixing between bed solids and the entering gas occurs in the grid region of a fluidized bed. Quantitative information on solid motion in this region is required for a better design of a distributor plate appropriate for a given operation.The objective of the present work is to measure solid particle velocities in the grid region and identify the effects of operating parameters on solids circulation and dead zone formation in this region. Methods available for two-phase flow measurement employ indirect techniques to obtain particle velocities, and often require probes that are large and disturb the flow.Perturbations to the flow can be avoided if optical techniques are used. They include the well known high-speed photography and the relatively new laser velocimetry. The main difficulty is, however, that they require an optical path to the measurement volume that is not available in the opaque threedimensional beds. Nevertheless, in the few configurations where such a path exists they provide a good technique for the evaluation and calibration of other probes. In this study a fine optical fiber probe was used to measure particle velocities in a two-dimensional fluidized bed using transit time correlation. CONCLUSIONS AND SIGNIFICANCEThe possibility of measuring solid velocity in the neighborhood of the distributor plate has been demonstrated. The measurements also show that the assumption of two-dimensional behavior in flat beds is valid except in the immediate neighborhood of the grid orifices, since no velocity differences were found across the thickness of the bed. Velocities measured using the optical fiber probe are presented in flow maps (Figures 8-10) that indicate solids circulation patterns and stagnant regions formed near the distributor plate.The transit time correlation approach using the optical fiber probe was found to be a convenient technique to measure particle velocities in two-phase flows with minimal interference to the flow. The technique is easy to apply and does not require prior knowledge of the fl...

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