Experiments were conducted in a cold model circulating fluidized bed having riser cross-sectional area of 100 mm x 100 mm, height of 4.8 m, bed temperature of 75 degrees C and superficial velocity of 8 m s(-1). Local sand having average diameter of 231 mu m was used as bed material. The experiments were conducted for three tube configurations: membrane tube, membrane tube with a longitudinal fin at the tube crest and membrane tube with two longitudinal fins at 45 degrees on both sides of the tube crest. The results show that membrane tubes with one and two longitudinal fins have higher heat transfer than membrane tubes and the heat is mainly transferred in the combination portion of tube and membrane fins. In addition, the membrane tube has the highest heat transfer coefficient. (C) 2008 Elsevier Ltd. All rights reserved.