A liquid solid circulating fluidized bed evaporator is designed and built to enhance the heat transfer and prevent and remove fouling in a two-pass evaporator. The effects of the operating parameters, such as circulation flow rate, amount of added particles, and height of the baffles, on the fluidization and distribution of solid particles in the two-pass circulating fluidized bed evaporator are systematically investigated using the charge-coupled device image measurement and acquisition system. Polyoxymethylene particle is used in the experiment. The circulation flow rate ranges from 10.66 m(3)/h to 19.14 m(3)/h, the amount of added particles changes from 0.5% to 2.0%, and the height of the baffles are 0.073, 0.1, 0.15, and 0.2 m. The particle distribution in the up-flow bed is uniform, whereas that in the down-flow bed is uneven. This study primarily investigates the particle distribution in the down-flow bed, which becomes increasingly uniform when the circulation flow rate is increased or when the height of the baffle is reduced, except when the baffle height is 0.2 m. When the circulation flow rate is low, the distribution becomes increasingly uneven as more particles are added. However, when the circulation flow rate is high, the amount of added particles has little influence on the particle distribution. Finally, two phase diagrams are established to show the optimal range of the operating parameters. These findings may serve as a valuable reference for the industrial application of the fluidized bed heat transfer enhancement and fouling prevention technology in multi-pass evaporators with baffles. (C) 2016 Elsevier B.V. All rights reserved.