Masaaki Naito

Effects of flow conditions on the efficiency of a sedimentation vessel

Abstract Removal efficiency in a sedimentation vessel is greatly subject to the motion of fluids. Ordinary rectangular sedimentation vessels are large in scale and are affected by various environmental conditions. Hence, the features of flow in such vessels are too involved to be strictly analysed based on hydrodynamic equations of fluid-motion. Consequently, no theoretical approaches to predict the removal efficiency in a practical sedimentation vessel are yet available, in spite of much previous work on this problem. In general, the properties of flow are characterized by two types of motion of fluids i.e. the one is that of local mean velocity and the other is homogeneous turbulence. In this paper, these types of motion are represented separately by simple flow models, named “diffusion model” and “circulation model”, respectively. These simple models can give a reasonable interpretation of the complicated motion of fluids in a sedimentation vessel, and the removal efficiency is also derived in a simple form. Moreover, the calculated values obtained by these models are found to be in good agreement with the experimental data.