Hydrodynamics and heat transfer in an air-water-glass bead system are investigated to study the effects of particle size (11-93 mum) and slurry concentration (up to 40 vol.%). The effect of particle size on gas holdup is only slight over the range of particle size investigated. This can be attributed to differences in rise velocities of different bubble fractions. Small bubble rise velocities are systematically lower for a particle size of 93 mum compared to 11- and 35-mum particles. Larger bubble rise velocities decreased with increasing particle size. Heat transfer coefficients decreased with increasing particle size at the column center, but no significant difference is observed at the column wall. At the column bottom, the heat transfer behaviour of the 11-mum particles is distinctly different from the 35- and 93-mum particles. With the 11-mum particles, there is a smaller effect of slurry concentration on local heat transfer coefficient. Estimated interfacial area results show a sharp decrease due to addition of fine particles into the liquid. The decrease is more dramatic as the slurry concentration is increased. (C) 2003 Elsevier B.V. All rights reserved.