Mixing Behaviour for the Mass and Heat of Granular Material in the Agitated Bed of Rotating Drums

摘要

Rotary kilns are widely used in the chemical and metallurgical industry. The thermal efficiency of a rotary kiln is preponderantly influenced by the amount of lateral mixing of the material bed. The dominant mechanism of the movement in the cross section is the rolling motion. A rolling bed is characterized by the continuous flow of particles with a nearly constant slope of the bed surface-defined as the dynamic angle of repose. The bed can be divided into two zones: (ⅰ) the stagnant zone where the particles transported as a rigid body with the rotation speed of the drum wall;(ⅱ) the mixing zone where the particles flow downwards with relatively higher velocities. The mixing was experimentally determined in two different ways. In the first way a drum was filled with two layers of sand with a different colour. The change of the colour in dependent on time was measured using a CCD-camera. In the second way the drum was filled with two layers of sand with a different temperature. The change of temperature in the bed was measured with thermocouples. The special measuring techniques will be explained in detail. The mixing behaviour will be shown for various rotational speeds, filling degrees and particle sizes.