Impact of particle flow regime on heat transfer in a rotary drum: Slipping vs. rolling regime

Rotary drying and calcination are essential to global manufacturing but remain among the most energy-intensive industrial operations. Due to limited understanding of internal bed dynamics, these processes are often operated at reduced throughput to maintain product quality. Distinct flow regimes arise, including the slipping regime, characterized by particles slipping at the wall, and the rolling regime, in which particle mixing is enhanced. In this work, discrete element method (DEM) simulations are used to investigate the influence of flow regime on heat transfer and mixing in a rotary drum. The flow regime is varied by adjusting wall friction, fill level, rotation rate, and particle properties. Results show that a particle bed in the rolling regime heats approximately twice as fast and achieves about five times greater temperature uniformity than in the slipping regime. Consequently, achieving equivalent product quality in the slipping regime would require roughly a twofold reduction in throughput. Introducing a baffle in the slipping regime induces behavior consistent with the rolling regime, significantly improving heat transfer and throughput. These findings provide a predictive framework for heat transfer in rotary drums, enabling operation at higher throughput with reduced energy consumption while maintaining product quality.