Heat transfer characteristics of two （coal slurry-gas, coal slurry-solid） and three (coal slurry-gas-solid) phase fluidized beds have been determined in a 15.2 cm-ID × 3.0 m-high QVF glass column fitted with an axially mounted cylindrical heater.
Effects of coal slurry velocity （4-12 cm/s）, air velocity (0-14 cm/s), slurry viscosity (14-24 mPa.s) and particle size (1.7-8.0 mm) on heat transfer coefficient were examined. In three phase slurry fluidized beds, heat transfer coefficient generally increased with gas velocity and particle size but it decreased with slurry viscosity. However, the coefficient went through a maximum value with liquid or coal slurry flow rate. The bed porosity at which the maximum heat transfer coefficient occured in coal slurry-solid system coincide with the maximum energy dissipation rate. The heat transfer coefficients in three phase coal slurry fluidized beds can be estimated from the surface renewal and isotropic turbulence theories.