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Evaluation of a Backscatter Imaging LDV System and its Application to a Pilot-Scale Circulating Fluidized Bed

ABSTRACT This study focuses on the evaluation and application of a backscatter imaging LDV (laser Doppler velocimeter) system (BILS) built by TSI Inc. (Shoreview, Minn.). This nonintrusive instrument has the ability to record particle images and velocity data simultaneously. A series of validation tests was conducted prior to measuring particle velocity in a turbulent system. A set of experiments was conducted to measure terminal velocity and particle size for five different-size cuts of near-spherical, Nu-Pareil particles, and the results were compared with the standard drag curve, which showed good agreement. The imaging data were used to estimate the sphericity (Φ) of the particles. The data confirmed that Φ was close to 1 (0.98 < Φ < 0.99). The system was then used to measure particle velocity in a cold flow circulating fluidized bed at various operating conditions. The effect of operating conditions, such as superficial gas velocity and solids circulation rate, on the solids velocity was studied. The mean solids velocity near the wall was found to increase with increasing superficial gas velocity and decreasing solids circulation rate. The granular temperature was also estimated and was found to increase with increasing distance from the wall. The granular temperature was found to lie in the range of 0.1–1.0 m2/s2 for the operating conditions studied. The granular temperature calculations also showed that the flow of particles moving downwards was more ordered than the flow moving up.