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On the motion of suspension thermals and particle swarms

Author(s): J. Bühler; D. A. Papantoniou

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Abstract: When a load dense particulate material is dumped from a barge, it descends in the water body as an irregularly shaped particle cloud. Provided that the particles are suflicienly small to be kept in suspension initially, the motion of the cloud is similar to that of a thermal of warm air rising in the atmosphere. Both types of buoyant clouds increase in size and slow down as they progress. For suspension clouds this thermal stage ends when their velocity has decreased to a value which is close to the individual settling velocity of the particles in a calm tluid. and the particles start falling out through the lower fringes of the cloud. After this transition is completed, a smooth, bowl-shaped particle swarm develops. An important difference between these two tlow regimes is that in the thermal stage the tluid inside the cloud moves in unison with the particles, whilst the interstitial fluid in the swarm stage remains nearly motionless as the particles rain through it. In this paper we propose a relation for the growth rate and velocity of thermals which is also applicable in the swarm stage. The resulting description thus covers the entire range of flows which are of interest for barge dumping. Experimental results are presented w hich allow a determination of the relevant flow constants in the swarm stage.


Year: 2001

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