Transverse flow of coffee beans in rotating roasters

The processing of particles in rotating cylinders is heavily influenced by the types of flow regimes within the cylinders during rotation. Conventional industrial coffee roasting is performed in rotating cylinders. Coffee beans undergo drastic physical and chemical changes during roasting and, due to that fact, the types of flow regime within the roaster will also vary. The types of flow regimes will, in turn, affect the uniformity of processing and ultimately the quality of the roasting. In this study, a small scale acrylic model of a cylindrical roaster was built and used to study the different forms of transverse motion of a bed of coffee beans during rotating motion. The model has internal mixing bars similar to those of industrial roasters. The model allowed the visualization of the flow regimes and their transitions, giving a preliminary idea of the regimes to be recommended for operation of conventional industrial roasters.