Sedimentation tanks are used in the process industry to separate the solid particles from the slurry to get the clarified liquid. A detailed study of the hydrodynamics of sedimentation tanks is presented here using an Eulerian-Lagrangian approach to study the motion of solids in the tank. The model, in its present form, is applicable only to nonflocculent discrete (Type I) settling. It is shown that a typical particle-eddy interaction can be characterized by a lower cut-off size below which the particles would be entrained by the eddy; and an upper cut-off size above which the particle would continuously settle through the sedimentation tank in spite of the recirculation. The effect of inlet configuration on the flow field as well as on the settling characteristics has been investigated. The simulations show that both the upper and the lower cut-off sizes for a sedimentation tank are considerably reduced by providing a tulip type of inlet with a conical deflector as compared to a straight inlet.

Sreenivas Jayanti

Department Of Chemical Engineering

flocculation

Hydrodynamics

Motion estimation

Particle size analysis

SLURRY PIPELINES

CLARIFIED LIQUIDS

PARTICLE-EDDY INTERACTIONS

SETTLING TANKS

Computational fluid dynamics

Hydraulics

liquid-solid separation

SEDIMENTATION TANK

Turbulence

Wastewater treatment

TULIPA

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Computational Study of Particle-Eddy Interaction in Sedimentation Tanks

Journal of Environmental Engineering

Transient response of two-phase flow is important in many analyses of nuclear reactor accident scenarios. In the present work, we study the response of vertical annular flow to a sudden or gradual pipe contraction. The three component fields of gas-liquid annular flow, namely, the liquid film, the entrained liquid droplets and the gas core, show different behaviour as they pass through an area change section because of their very different inertias. Pressure variation through the contraction is a result of the integrated effect of these responses. In order to throw light on these, pressure profiles along the upstream and downstream sections of the contraction have been measured in air-water flow through a vertical converging pipe section for diameter ratios of 1.5 and 2.0 and for half-cone angles of 8° 15° and 90°. The gas-droplet field interaction has been studied using computational fluid dynamics simulations while the gas-film flow interaction has been studied using an analytical model for film flow. These studies highlight the role of droplet inertia as the principal contributor to the pressure change in the contraction. A semi-empirical model has been developed for the pressure loss coefficient in the contraction. © 2019

Annals of Nuclear Energy

Study of gas-liquid upward annular flow through a contraction

Gas–liquid annular flow draws different responses from its three constituents, namely, the liquid film, the entrained liquid droplets and the gas core, as they flow through a diverging section in a pipe. The resulting change in the pressure profile is a combination of several effects associated with the dynamic interactions among these three fields. Accurate simulation of the response using Eulerian–Eulerian computational fluid dynamics is not feasible because the processes are inherently complex and a framework of relevant and validated constitutive relations describing the physical processes is not yet available. In the present work, a simpler approach is adopted by studying the interactions individually in idealized settings, and bringing together the separate effects into a phenomenological model for pressure loss in upward vertical annular flow. The overall pressure change is expressed as a sum of three contributors: change in area of cross-section available for gas flow, change in the effective interfacial roughness leading to peaking of the velocity profile, and droplet-gas momentum exchange in the immediate downstream of the expansion. Using air–water experimental data from two expansion ratios and three half-angles of the diverging sections, a mechanistic correlation is proposed to evaluate the overall pressure loss coefficient. © 2018 Elsevier Inc.

Applied Mathematical Modelling

A mechanistic model for expansion loss coefficient in upward vertical annular flow

Experiments on dispersion of floating solids into continuous liquid medium were carried out with low density microspheres with particle density of 680kg/m3 and size 100, 230 and 325μm in different liquids having density varying from 778 to 1830kg/m3 and kinematic viscosity varying from 0.3 to 19cP. A four-bladed radial impeller and axial paddle impellers with upward and downward flow directions were employed. The critical impeller speed (Ncrit) required for uniform dispersion of particles throughout the continuous medium was experimentally determined for various conditions. Experimental results indicate that the radial impeller with impeller location near the surface required minimum impeller speed for uniform dispersion. Strong effect of the density difference between the particles and the liquid and submergence of the impeller was noted. Based on the experimental results, a correlation in terms of relevant dimensionless groups was proposed for calculating Ncrit for the three impellers. The overall correlation indicates that the critical impeller speed is not significantly affected by liquid viscosity and particle diameter but that it is strongly influenced by the impeller diameter and the density difference. These results are in agreement with trends reported in the literature. © 2015 The Institution of Chemical Engineers.

Chemical Engineering Research and Design

Effect of impeller type and density difference on the draw down of low density microspheres

We present a modeling framework for the simulation of the hydrodynamic features of a liquid solid circulating fluidized bed (LSCFB) using computational fluid dynamics (CFD). Using an Eulerian-Eulerian approach to deal with the two-phase flow aspects and the kinetic theory of granular flow (KTGF) approach to deal with the solid-fluid interaction, we simulate the complete flow loop of an LSCFB using three-dimensional, time-dependent CFD calculations. We show that the essential features of the two-phase flow in the riser, the downcomer, the liquid-solid separator at the top and in the solids return feed pipe at the bottom are captured well in these simulations. The role of the flow distributors in establishing circulation is critically analyzed with the aid of post-processing tools. Comparison with literature data shows qualitative agreement with known trends of important hydrodynamic parameters and highlights the need for calibration of the constitutive equations for LSCFB applications. © 2013 Elsevier B.V.

Powder Technology

Numerical simulation of the hydrodynamics of a liquid solid circulating fluidized bed

Computational study of particle-eddy interaction in sedimentation tanks

Environmental Geology

January 2004

Water Science and Technology

The Use of Computational Fluid Dynamics for Improving the Design and Operation of Water and Wastewater Treatment Plants

Water Research

Velocity and solids distribution in circular secondary clarifiers: Full scale measurements and numerical modelling

Process Safety and Environmental Protection

Recent Progress in the Numerical Modelling of Wastewater Sedimentation Tanks

Journal	Journal of Environmental Engineering
ISSN	07339372
Open Access	No