increasing entropies of mixng

Fig. 8.10. (a) Basis of the discrete-particle modeling work done by Schutyser et al. (2001, 2002). The arrow originating from the center of each particle shows its velocity (magnitude and direction). (b) Concept of the entropy of mixing. The more random the distribution of particles in relation to their original position, the greater the entropy of mixing

The effects of drum rotational speed (0.5, 2, and 5 rpm), drum diameter (0.15, 0.3, and 1 m) and the fraction of the drum occupied by the bed (0.2, 0.33, and 0.4) were investigated. In the various experiments and simulations, between 1.5 and 10 rotations were necessary in order to reach the well-mixed state. The number of rotations required was essentially independent of the drum rotational speed, although of course for faster speeds the required number of rotations was completed in a shorter time. The effect of drum diameter and fractional filling of the drum were related to their effects on the ratio of the exposed surface area of the bed to the bed volume (RB, m-1), with the number of rotations required to achieve the well-mixed state initially falling quickly as this ratio increased, reaching a plateau of 1.5 rotations when this ratio had a value of 20 (Fig. 8.11(a)).

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