Overall heat transfer between circulating fluidized beds (CFB) and the ribbed membrane fins of a water wall tube was investigated experimentally in a cold model circulating fluidized bed riser. The riser had a cross sectional area of 0.1 x 0.2 m(2) and the height from the distributor plate to the riser exit was 3.9 m. Three isosceles triangular cross section prisms having a height to base width ratio (e/B) of 0.54 corresponding to the height to riser diameter ratios (e/D) of 0.019, 0.038 and 0.06, respectively were used as ribs. The ribs were installed transversely on the fins with three rib spacings (S) of 0.4 m, 0.5 mand 0.6 m. Local sand having an average diameter of 315 pm was used as the bed material. It was found that the heat transfer coefficients and the cluster solid fractions of the ribbed membrane fins were higher than those of the membrane fin, and varied with the rib spacing and the rib height to diameter ratio in the same manner. In addition, cluster contact time of the ribbed membrane fins was shorter than that for the membrane fin without ribs. (C) 2018 Elsevier B.V. All rights reserved.