An experimental study has been carried out on both the transient and steady state heat transfer of a gas-solid two-phase mixture flowing through a cylindrical packed bed reactor under the constant wall heat flux conditions. A logarithmic mean temperature difference (LMTD) method is used to process the steady state data to obtain the overall heat transfer coefficient. The effects of solids loading, particle size and flow Reynolds number are investigated. The results show that the introduction of suspended particles greatly enhances the heat transfer and the enhancement increases approximately linearly with solids loading and the effect of particle size is relatively weak under the conditions of this work. A correlation is proposed based on the experimental data, which relates well the Nusselt number to the Reynolds number, the Archimedes number and the suspended solids loading. Given other conditions, the Nusselt number at the constant wall heat flux conditions is much higher than that under the constant wall temperature conditions. It is shown that the Reynolds number and particle loading have a greater influence on the Nusselt number under the constant heat flux conditions than that under the constant wall temperature conditions investigated by the authors in a previous study. (c) 2006 Elsevier B.V. All rights reserved.