| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 83 === The segregation phenomenon and particle expansion are
experimentally studied in a vertical shaker. Two different
sizes of glass beads are well-mixed in the shaker before the
experiment started. When the vibrational acceleration lower
than 1.0 g (g is the gravitational acceleration), there is no
separation of the mixture. Increasing the acceleration from 1.0
g to 1.75 g, many voids are formed in the bed which causes the
smaller particles falling through the voids to the bottom.
This is called as segregation. The segregation coefficient is
found to increase with the acceleration. If the acceleration is
higher than 1.75 g, the bed begins to expand and the particles
move much more randomly causing larger voids formed in the bed.
Therefore, the larger particles have more probabilities to
falling through the voids resulting in the decrease of the
segregation coefficient. The bed height is increased with the
acceleration due to the bed expansion until the acceleration
reaches 2.7 g. With higher acceleration, the voids are so
large that the smaller and the larger particles have the same
probabilities to falling down and then no segregation effect
occurs. Besides the sizes of particles, the particle density is
an important factor to influence the segregation. The glass
beads and steel beads are used in this experiment. If both
materials have the same size, no segregation occurs. If the
sizes are different, the combination of small size -- small
density & large size -- large density has the greatest
segregation coefficient. If the smaller particles have higher
density than the larger particles, the segregation effect is
the worst. It can be concluded that the lighter particles and
the smaller particles tend to move to the bottom of the bed
during the segregation.
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