Suspensions of Granular Particles Generated by an Upward Flow

Citation

McMichael, Francis Clay (1963) Suspensions of Granular Particles Generated by an Upward Flow. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/E8SA-YB56. https://resolver.caltech.edu/CaltechTHESIS:04242012-142541079

Abstract

A laboratory study was made of the local properties of suspensions of granular particles generated by an upward flow of water. Four granular materials covering a range of particle sizes having particle Reynolds numbers between 10 and 70 were studied by making detailed measurements within ten suspensions. Measurements were made of the mean properties of over one hundred suspensions. Concentrations in the suspensions generated by upward flow were generally greater than those of typical hindered settling experiments, but less than those of typical fluidization experiments by chemical engineers.

Measurements of the mean concentration for an entire suspension and the ratio of superficial velocity to particle free-fall velocity yielded a separate relationship for each material studied. These relationships are strongly dependent on the standard deviation of particle sizes for the parent materials.

Recognizing that granular materials are never perfectly uniform, measurements of concentration and particle size were made on a local basis. The suspensions were found to sort themselves with the fine particles near the top and the coarse particles at the bottom, and the local concentration was observed to decrease from the bottom to the top of the suspension.

Granular particles with mass densities approximately two and one-half times the density of water and having particle Reynolds numbers in the range from 10 to 70 produce highly turbulent systems when fluidized with water. It was observed that there is local generation of turbulence throughout the suspension with the highest intensity of turbulence being in the region where the local concentration is the largest.

Measurements of the hindered settling velocity of a suspension and the superficial velocity necessary to maintain the suspension show the two quantities to be identical for all practical purposes. The turbulence was observed visually to be less for the settling suspension than for the fluidized suspension.

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