This paper presents an experimental study on the radial distributions of heat transfer coefficients in a fast fluidized bed operating at low temperatu re. The following conclusions can be reached from the experimental results: 1. The heat transfer coefficient profiles are complex in a fast fluidized bed

generally

flat in the centre and steep in the region near the bed wall. 2. Solids concentration is the dominant factor influencing heat transfer

while the effect of gas and particle velocities is comparatively less significant. 3. When solids concentration is high

the heat transfer coefficient profile is consistent with that of solids concentration. For low solids concentration

the profile is affected by the radial distribution of gas and particle velocities

and a minimum point of heat transfer coefficient will appear in the region of radial ratio from 0.5 to 0.8. For rather low solids concentration and high gas velocity

gas convection becomes notable

the heat transfer coefficient profile becomes more complex with higher values in the region near the axis than those near the bed wall. The following equation is recommended to correlate the local heat transfer coefficients in fast fluidized beds: where a

n

1 and n2 are functions of radial positions

while ε is a function of axial position