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In recent years, circulating fluidized beds (CFBs) have been extensively employed in a variety of industrial applications related to coal combustion and gasification, solid waste incineration, catalytic cracking of oil, and so on. To accomplish successful and reliable operation of CFBs, a number of in- Detailed researches in this direction will considerably help in the optimum and economic designs of CFB boilers. To aid in this direction, we have measured the three-dimensional particle velocities in a square-section CFB cold model under certain operating conditions at ambient temperature and pressure. Particle turbulent intensities and bed cross-sectional averaged voidage along its height are also measured. A majority of the investigations have been conducted in circular cross-section CFBs, but industrial preference is for a square cross-section boiler, and hence we have adopted this configuration in our present work. Our measurements, while confirming the coreannulus flow structure for CFBs, also provide a more comprehensive microscopic detail of particle velocities in the two regions, in addition to providing a basis for particle aggregation. Experimental Apparatus and ResultsThe schematic of the CFB employed in the present work is shown in Figure 1. The riser section is 3 m long and has a square cross-section, 222 mm by 222 mm. Seventeen pressure taps (13) are installed along the metal bed wall starting from a height of 250 mm' above the air distributor plate (3) and up