A laboratory study was made of the local properties of suspensionsof granular particles generated by an upward flow of water. Fourgranular materials covering a range of particle sizes having particleReynolds numbers between 10 and 70 were studied by making detailedmeasurements within ten suspensions. Measurements were made of themean properties of over one hundred suspensions. Concentrations inthe suspensions generated by upward flow were generally greater thanthose of typical hindered settling experiments, but less than those oftypical fluidization experiments by chemical engineers.
Measurements of the mean concentration for an entire suspensionand the ratio of superficial velocity to particle free-fall velocity yieldeda separate relationship for each material studied. These relationshipsare strongly dependent on the standard deviation of particle sizes forthe parent materials.
Recognizing that granular materials are never perfectly uniform,measurements of concentration and particle size were made on a localbasis. The suspensions were found to sort themselves with the fine particlesnear the top and the coarse particles at the bottom, and the localconcentration was observed to decrease from the bottom to the top ofthe suspension.
Granular particles with mass densities approximately two andone-half times the density of water and having particle Reynolds numbersin the range from 10 to 70 produce highly turbulent systems when fluidizedwith water. It was observed that there is local generation ofturbulence throughout the suspension with the highest intensity of turbulencebeing in the region where the local concentration is the largest.
Measurements of the hindered settling velocity of a suspensionand the superficial velocity necessary to maintain the suspension showthe two quantities to be identical for all practical purposes. The turbulencewas observed visually to be less for the settling suspension thanfor the fluidized suspension.
