A combined approach of discrete particle simulation and computational fluid dynamics is used to study the heat transfer in a fluidized bed with a horizontal tube. The approach is first validated through the good agreement between the predicted distribution and magnitude of local heat transfer coefficient with those measured. Then, the effects of inlet fluid superficial velocity, tube temperature and main particle properties such as particle thermal conductivity and Young s modulus are investigated and explained mechanistically. The relative importance of various heat transfer mechanisms is analyzed. The convection is found to be an important heat transfer mode for all the studied conditions. A large convective heat flux corresponds to a large local porosity around the tube, and a large conductive heat flux corresponds to a large number of particle contacts with the tube. The heat transfer is enhanced by the increase of particle thermal conductivity while it is little affected by Young s modulus. Radiative heat transfer becomes increasingly important as the tube temperature is increased. The results are useful for temperature control and structural design of fluidized beds.