Heat transfer between gas–solids suspension and immersed surface in an upflow fluidized bed (riser)

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Axial and radial distributions of heat transfer were studied in a 15.1 m high, 100 mm diameter gas–solids upflow fluidized bed (riser) with FCC particles. Heat transfer coefficients between an immersed surface and the gas–solids flow suspension were measured using a miniature cylindrical heat transfer probe for wide ranges of superficial gas velocity (3.5–10 m/s) and solids circulation rate (50–200 kg/m 2s). Local solids concentration was also obtained by an optical fiber probe under the same operating conditions. The results show that the axial and radial distribution profiles of the heat transfer coefficient are consistent with those of the solids concentration, with higher heat transfer rate near the wall and in the bottom dense region. In general, the solids concentration is the dominate factor influencing the local heat transfer in the riser, however gas velocity has a significant effect on the heat transfer behavior under dilute conditions and at high gas velocities where gas convection begins to play an important role.