THE TRANSITION IN THE SEDIMENTATION PATTERN OF A PARTICLE CLOUD

Experiments were carried out to study the sedimentation of a two-dimen sional particle cloud. When a large number of particles (glass beads) of uniform size are released from a two-dimensional opening into a col umn of fresh water, the mixture initially descends as a thermal; howev er, after some time, the particles start settling individually, thus l eaving the parent fluid behind. For a given type of particle, the crit ical depth z(c) at which this transition occurs, measured from a virtu al origin, was found to change as z(c)w(s)/v similar to (Q/vw(s))(alph a), with alpha congruent to 0.3, where w(s) is the terminal velocity o f a single particle, v is the kinematic viscosity, and Q is the total buoyancy of the released particles per unit length. The descending vel ocity and the spatial growth of the particle cloud were found to depen d on its sedimentation characteristics.