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Effects of gravity on cohesive behavior of fine powders:implications for processing Lunar regolith

机译：Effects of gravity on cohesive behavior of fine powders:implications for processing Lunar regolith

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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 fluidiz-ing, 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 'cohe-siveness' 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 100g_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.

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