A mechanistic model to evaluate heat transfer rates between the dense phase of gas fluidized beds and immersed surfaces has been recently presented by the authors. This model, denoted Generalized Heterogeneous Model (GHM), is formulated in terms of effective thermal properties for particles and interstitial gas. It has been conceived with the purpose of achieving a generalized formulation accounting simultaneously for conductive, gas convective and radiant effects.The model was previously tested as regards its capability to predict radiative heat transfer rates in beds at high temperature and gas convective contribution in beds of large particles and high operating pressures.It is the principal object of this contribution to evaluate the performance of the GHM for a wide range of particle sizes, covering from the purely conductive regime to the gas convection dominant regime.Also, the main assumptions incorporated in the model are revised and some modifications are introduced, mainly on the basis of the results obtained by Mazza et al. (1997b).