AbstractA rotating drum with lifting flights is an important piece of industrial equipment used to contact granular solids with a gas stream. Applications include the drying of materials such as wood chips, coal, grain, and metallurgical ores, the cooling of fertilizer pellets and more recently the combustion of coked oil sand. A new mathematical model for a rotating drum with lifting flights that predicts the residence time of particles is proposed. Particle motion is considered in both the airborne phase and the dense phase. Moreover, the holdup and the axial flow rate of particles in the two phases are determined separately. Overall, the model is more flexible than previous models. The drum may be inclined or horizontal with cocurrent or countercurrent flow, may have any type of lifting flights and may be underloaded or overloaded.