Storage and Flow of Solids
01 Jan 1964-
About: The article was published on 1964-01-01 and is currently open access. It has received 585 citations till now. The article focuses on the topics: Flow (mathematics).
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TL;DR: In this paper, the change in powder flow behavior with g-level is clearly demonstrated by observing the transition from avalanching flow to smooth flow as the effective glevel is increased, and vice versa.
Abstract: It is well known that powders become more ‘cohesive’ as their mean particulate size decreases. This phenomenon is evidenced by such characteristics as poor flowability, clumping, avalanching, difficulty in fluidizing, and formation of quasi-stable, low-density configurations that are easily compacted. Gravity is often the primary driving force for powder movement in common powder processing and transfer operations. Because of this, gravity plays a role in how the flow behavior of powders is typically characterized. As a result, the ‘cohesiveness’ of a powder varies with gravity-level, with a powder appearing more ‘cohesive’ as the effective gravity level is decreased. In this work the change in powder flow behavior with g-level is clearly demonstrated by observing the transition from avalanching flow to smooth flow as the effective g-level is increased, and vice versa. Experiments with micron-scale pharmaceutical powders in a centrifuging, rotating-drum micro- avalancher, covering g-levels from 12.5 to 1,200 (a factor of 100 variation in g-level) clearly demonstrate the changes from clumping (with no flow), to avalanching flow, to free-flowing behavior as the effective g-level is increased. A mere factor of four change in effective g-level (from 25 g
o
to 100 g
o
) was sufficient to show a significant change from avalanching behavior to free flowing behavior for more than one powder tested. Extrapolation of this same behavior to gravity levels below our terrestrial level (such as to the 1/6 g
o
conditions on the moon) would indicate that Lunar regolith will exhibit more ‘cohesive’ behavior in processing, transfer and handling equipment than the same powder would exhibit terrestrially. Thus, Lunar in-situ resource utilization (ISRU) processes may need to use larger size openings, steeper slopes or non-gravity driving forces in processing, transfer and handling equipment than would be used for comparable powders and processes on earth.
41 citations
TL;DR: The need for an improved experimental setup which would be capable of measuring the flow properties of powders under very small consolidation stresses with a high shear stress resolution is highlighted to allow the accuracy, precision and applicability of the shear test to be improved for pharmaceutical applications.
40 citations
TL;DR: In this article, an experimental and numerical study of dry, frictional powder flows in the quasi-static and intermediate regimes using the geometry of the Couette device is performed. But the results are limited to the case of a single cylinder and are not applicable to other configurations of Couettes, such as an eccentric Couette and a more complicated geometry where a cylindrical body is introduced in the middle between the rotating and stationary cylinders and obstructs part of the shearing gap.
40 citations
TL;DR: In this paper, the evolution of an amaranth seed in a wedge-shaped model made of Plexiglas was investigated using the digital particle image velocimetry (DPIV) optical technique.
40 citations
TL;DR: In this article, a model of the relationship between heat transfer at a single tube and the velocity profile between two neighbouring tubes is proposed. But the model is not suitable for the case of a single-tube setting.
Abstract: The indirect heat transfer of steam-heated tube bundles in a moving bed has been examined in an experimental apparatus. Heat transfer in single tubes is typified by a characteristic flow of the bulk solids along the outer tube wall surface. A cuneiform rest zone is created at the upper tube wall (stagnation point), in which the particles remain for a long time. An ‘insulating’ effect is exhibited by the dammed bulk zone and is responsible for the poor heat transfer in this area. Near the sides of the lateral tubes heat transfer is good and icreases with increasing mass flux and bulk solids velocity. Bubbling occurs at the lower tube wall and the heat transfer again decreases due to the small number of wall-particle contacts. The experimentally confirmed ‘trace theory’ describes the temperature profile at the outlet of a moving bed heat exchanger, being characterized by very good cross-mixing of the bulk solids which allows the intergral heat transition to be calculated. A modelling approach to the heat transfer and bulk solids movement in the moving bed provides a physical model which describes the dependence of the heat transfer at a single tube on the flow profile between two neighbouring tubes. In order to determine the flow profile, the continuity equation is solved vectorially, allowing an analytical relationship of the velocity profile between two tubes to be obtained via the coaxiality of stress and deformation. To allow such a calculation, the heat-transfer model makes use of the residence and contact time behaviour resulting from the velocity profile, with the different components of heat transfer at a tube being determined from the friction properties of the specific bulk material. Calculation of the integral heat transfer in the moving bed may be achieved via heat transfer at a single tube. By using the theory of ‘extended contact time’, the total residence time of the bulk at the first tubes may be considered as a case history for the other tubes. The integral overall heat-transfer coefficients of moving bed heat exchangers thereby determined have been verified experimentally.
40 citations