Study of flow characteristics in a secondary clarifier by numerical simulation and radioisotope tracer technique

A CFD methodology for the design of sedimentation tanks in potable water treatment

“…6(a) and (b), the particles do not affect the flow field. This observation is attributed to the small particle loading in our sedimentation tank and is similar to that made by Kim et al [2], who worked in a secondary clarifier with a neutral density influent flow. On the contrary, in the case of high inlet fluid density (high solids concentration) combined with a low fluid velocity, the horizontal inlet flow does not even reach the flow control baffle, but plunges down toward the tank bottom as a density waterfall due to the low Froude number.…”

“…The percents for classes 6-13 (see Table 1) are very close to 100% indicating that the particles with the eight highest settling velocities would be settled almost completely regardless of the configuration used. Therefore, the improvement in the overall efficiency of solids removal is only achieved by improving the settling of particles with lower settling velocities (classes [1][2][3][4][5]. This observation is similar to that obtained by Huggins et al [1], who used a CFD model to evaluate the impact of potential raceway design modifications on the in-raceway settling of solids.…”

“…Krebs et al [8] used the Phoenics code to model different inlet arrangements and evaluated the effect of inlet baffle position and depth. Deininger et al [9] improved the Champion3D numerical model and predicted the velocity and solids distribution in a circular secondary clarifier, whereas Kim et al [2] have recently performed a numerical simulation in a 2D rectangular coordinate system and an experimental study to figure out the flow characteristics and concentration distribution of a large-scale rectangular final clarifier in wastewater treatment.…”

“…From a hydraulic point of view, a distinction has to be made between primary and secondary settling tanks in terms of density effects. In secondary clarifiers the increased density (due to large particle mass fraction) gives rise to a couple of characteristic flow features such as density waterfall phenomenon near the inlet of the clarifier and solid cascading phenomenon in clarification of suspended solids [2]. In the case of potable water treatment the solid mass fraction is even smaller than that of the primary clarifiers.…”

Investigation of liquid phase axial dispersion in Taylor bubble flow by radiotracer residence time distribution analysis

“…The unique ability of this technology is that it can provide information that may not be obtained by other techniques. This technology has been widely used in developed countries to help solve industrial problems [6][7][8][9]. It is also flourishing in developing countries [10][11][12][13][14][15] but facing a major constraint due to the unavailability of radiotracers at the time of requirement.…”