Convective heat transfer between gas and cluster in a circulating fluidized bed (CFB) riser is numerically studied using a three-dimensional computational fluid dynamic (CFD) model. Distributions of gas velocity and temperature as well as the gas-cluster heat flux and convective heat transfer coefficient are obtained. Variations of heat flux of each particle in the cluster are predicted. The heat flux of the individual particle inside the cluster is smaller than that of an isolated particle. The convective heat transfer coefficients increase with the increase of cluster porosity and Reynolds number. The convective heat transfer coefficients of the downward moving cluster are larger than that of upward moving cluster. Numerical results of an isolated particle are in agreement with data from previously published correlations. (C) 2010 Elsevier Ltd. All rights reserved.