Rotating drums are widely used in industries to handle and process particulate materials and heat transfer is often involved in these processes. This work numerically investigated heat transfer inside a drum mixer by coupling the discrete element method (DEM) with a conductive heat transfer model. The mixer was fitted with different types of lifters and rotated at various speeds so their effects on heat transfer characterised by heat transfer coefficient (HTC) could be investigated. The simulation results showed that the specific HTC of the particle flow increased with increasing rotating speed but decreased with the number and height of the lifters. While all types of lifters sped up heat transfer, the straight lifers were more efficient than the arc shape lifters. To better understand the mechanisms of heat transfer, the specific HTC was linked to the particle-wall contact area and dynamic behaviour of particles. The change of lifter configuration, i.e. lifter height, number and shape, mainly affected the particle-wall contact area while the change of mixer rotating speed affected particle mixing behaviour. (C) 2016 Elsevier B.V. All rights reserved.