Gas-solid fluidized beds have been widely used in heat transfer processes,and so there have been many studies focused on increasing heat transfer in such units.In the present work,a pilot scale cold mode experimental rig was constructed to assess the effects of hydrodynamics on bed-to-wall heat transfer and to investigate various means of enhancing heat transfer in a dense gas-solid fluidized bed with external solid circulation.The experimental results show that heat transfer in the dense region played a dominant role in total bed-to-wall heat transfer,accounting for more than 88％of the total heat transfer load.Heat transfer could be lowered as a result of solids bypass that occurred because of external solids circulation,but this effect was weakened by the radial mixing of particles.The heat transfer characteristics identified in this study indicate that a specially designed baffle can be used to enhance bed-to-wall heat transfer.After installing such baffles in the fluidized bed test structure,a 70％increase in the total heat transfer coefficient was obtained.