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Baffled flow may provide better conditions for sedimentation by influencing velocity profiles.

It was found that the baffle setting and its position relative to the inlet and outlet influences the flow field and the development of flow. It was quantitatively found that the intermediate baffle not only influences the flow field in its downstream, but also affects the flow pattern in its upstream. Mean flow analysis shows how a baffle can alter the hydrodynamics of the flow field. Effects of baffle positioning were also determined. Thus, in this study, velocity measurements were performed by a three-dimensional Acoustic Doppler Velocimeter (ADV) to investigate baffle effects on the velocity distribution in a primary rectangular sedimentation tank, quantitatively. The provision of a baffle as a geometrical modification of a tank may influence the flow field for better sedimentation. For proper design of such tanks, the formation of recirculation zones should be avoided. In primary sedimentation tanks, short-circuiting enlargement of dead zones and high flow mixing problems are caused by circulation regions (dead zones), which can reduce the optimal sedimentation of particles. These equations will be useful for the design of grit chambers and settling basins undergoing class-I settling. Besides other parameters, the design equations involve the completely removed minimum particle size, the specific gravity of the sediment particles, and the kinematic viscosity of water. Using these equations the design equations have been obtained for the length and width of the settling tank. The removal efficiency equation yields the minimum particle size completely removed by the sedimentation tank. The removal efficiency equation considers the size distribution of particles, and the scour velocity equation is based on the Rouse equation. This technical note presents closed-form equations for the removal efficiency and scour velocity of particles. The design procedure would be more rational if it were based on the removal efficiency and the scour criterion of the deposited particles.

The present practice for the design of primary settling tanks is based on the overflow rate corresponding to the percentage removal using isoremoval plots.