Heat transfer characteristics of different powders in gas fluidization are investigated by means of a combined approach of discrete element method and computational fluid dynamics. First, the heat transfer characteristics in three flow regimes of group A powders are examined. Then, the effects of the Hamaker constant and particle size, both related to the van der Waals force, are investigated in detail. The results confirm that the convective heat transfer is dominant, and radiative heat transfer becomes important when the bed temperature is high. However, conductive heat transfer also plays a role depending on the flow regimes and material properties. Significant effects of the Hamaker constant and particle size are observed under certain conditions. Finally, an effort is made to quantify the effects of the Hamaker constant, particle size, and inlet gas velocity. The findings should be useful for better understanding and prediction of the heat transfer in gas fluidization.