Dynamics of Growth and Breakage of Alum Floc in Presence of Fluid Shear

by John D. Boadway, Assoc. Prof.; Dept. of Civ. Engrg., Queen's Univ., Kingston, Ontario, Canada,


Serial Information: Journal of the Environmental Engineering Division, 1978, Vol. 104, Issue 5, Pg. 901-915


Document Type: Journal Paper

Errata: (See full record)

Abstract: Particles of flocculating clay and alum are found to grow in fluid shear by collision with each other to form larger particles of lower density and strength until they cannot withstand the shear stress and break as fast as they are formed. The growth and breakage of flocculating particles was studied by photographing suspensions while they were being sheared between coaxial cylinders. Data on growth of mean sizes agreed with a simplified mathematical model and was then used to derive equilibrium mean size and growth rates for experiments with varying concentration and velocity gradients, thus establishing relationships for effects of these variables. A computer simulation was made of particle growth using a more complex set of assumed conditions of growth and breakage mechanism and found to be in fair agreement with observations.

Subject Headings: Particles | Shear stress | Shear strength | Flocculation | Soil strength | Data processing | Clays | Soil stress

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