The effects of secondary air ratio (0 similar to 50%) and injection types (radial or tangential) on the bed-to wall heat transfer coefficient have been determined in a circulating fluidized bed (0.1 m-I.D, x 5.3 m-high). The bed-to-wall heat transfer coefficient increases with increasing particle suspension density, The heat transfer coefficient by gas convection increases, but the overall convective heat transfer coefficient decreases with increasing the radial injection of secondary air, The convective heat transfer coefficient increases, but the particle convective component decreases with the tangential secondary air injection, A model, based on the model of Basu (1990), is proposed to predict the bed-to-wall heat transfer coefficients in a circulating fluidized bed (CFB) with the tangential secondary air injection system.