A method to resolve particle-particle and particle-wall unsteady conduction heat transfer is developed within the framework of the soft sphere collision model. The unsteady heat transfer model is incorporated in an existing CFD-DEM framework. The model is derived from the analytical solution of one-dimensional unsteady heat conduction between two semi-infinite objects. The model considers the area and time of contact with appropriate scaling for compatibility with the soft sphere model. The model is validated against experimental data available from the literature for three cases. The cases considered are pairwise particle-particle collision, single particle-surface collision, and that of the decay of temperature of a heated particle in a fluidized bed, including convection and particle-particle-wall conduction heat transfer. The results obtained are in good agreement with the experimental data. Next, the model is applied to a fluidized bed with an immersed tube to characterize the heat transfer mechanisms and the effective heat transfer coefficient. The influences of fluidization parameters such as gas velocity and particle diameter on heat transfer mechanism is investigated. © 2019 Begell House Inc. All rights reserved.