Boundary Layer Separation Concept of Settling Tanks

by Yishu Chiu, (M.ASCE), Asst. Prof.; Dept. of Civ., Mech. and Envir. Engrg., George Washington Univ., Washington, D.C.,

Serial Information: Journal of the Environmental Engineering Division, 1974, Vol. 100, Issue 6, Pg. 1213-1218

Document Type: Journal Paper


The conventional horizontal-flow central-feed circular tank is usually regarded as less efficient in sedimentation than the rectangular type. For a hydraulic study of settling tanks a concept of boundary layer separation is introduced. From a theoretical aspect, it is indicated that separation does occur in the conventional horizontal-flow central-feed circular tank, but not in the rectangular tank. Separation results in eddy currents, which reduce efficiency in removal of settleable solids. In this type of circular tank, the theory also shows that the liquid surface rises in its flow direction. This causes unstable flow, which in turn results in poor sedimentation.

Subject Headings: Cylindrical tanks | Boundary layers | Sedimentation tanks | Advection | Sediment | Hydraulics | Eddy (fluid dynamics) | Solid mechanics

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