Heat transfer at the top of a CFB riser with smooth exit

The present paper reports the results of an experimental investigation on heat transfer between the gas-solid suspension and heat transfer tubes of different configurations located at the top of a CFB riser with a smooth exit. Experiments were conducted to determine the total (gas convective and particle convective component) surface-average heat transfer coefficient from the tube to suspension for four different tube configurations placed in the core of the top of a 5.5 m tall, 100 mm × 100 mm square cold CFB riser with a smooth exit. All the tubes were made up of copper having 9.6 mm OD with 0.6 mm thickness. Sand was the bed material and covered a range of mean particle size (143-363 μm), fluidizing velocity (4-8 m/s), and solid recycle flux (21-72 kg/m2s) resulting in the average cross-sectional suspension density of 10 to 42 kg/m3. The measured heat transfer coefficients were in the range of 50-130 W/m2K. In general the heat transfer coefficients increased with suspension density, solid recycle flux, and gas velocity but decreased with increasing particle size. The present experimental data were compared with published heat transfer results under somewhat similar conditions and an empirical heat transfer correlation was developed in terms of important design and operating parameters.