Axial mixing of particles in rotary dryers and coolers.

For the purpose of making clear the mechanism involved in the axial mixing of particles in rotary dryers and coolers, the axial mixing of particles in batch systems was measured. The diffusion model has been applied to the axial mixing of particles in batch and continuous systems and the influence of the operating variables on the diffusion coefficient in batch systems and on the axial dispersion coefficient in continuous systems has been examined. As a result, it is found that the influence of the operating variables on both the coefficients is essentially the same and that the ratio of diffusion coefficient to axial dispersion coefficient is approximately equal to 0.7 under the same experimental conditions. This result indicates that as the axial mixing of particles in the batch system is considered to be due to collision and bounce between the particles falling from the flights and the bare wall, the lifting flights and the particles deposited in the lower part of the dryer collision and bounce may be a major mechanism involved in the axial mixing of particles in continuous rotary dryers and coolers.