Extended Analytical Turbulent Diffusion Model for Particle Dispersion and Deposition in a Horizontal Pipe: Comparison with CFD Simulation

Abstract

A 2D analytical turbulent diffusion model for particle dispersion and deposition at different heights along the pipe flow and circumferential deposition has been developed. This liquid-solid turbulent diffusion model presented in this paper has emanated from an existing gas-liquid turbulent diffusion model. This model can be used as a handy tool for quick estimation one and twodimensional deposition fluxes of particles in water distribution networks. A comprehensive 3D numerical investigation has been carried out using multiphase mixture model available in "Fluent 6.2" to verify the above analytical model. Different particles sizes and densities were used for 3D numerical investigations. The deposition was studied as a function of particle diameter, density, and fluid velocity. The deposition of particles, along the periphery of the pipe wall and at different depths, was investigated. Both the models findings matched with qualitative phenomena such as deposition of heavier particles at the bottom of the pipe wall were higher at lower velocities and lower at higher velocities. The lighter particles were found mostly suspended with homogeneous distribution. Smaller particles were also suspended with marginal higher concentration near the bottom of the pipe wall. This marginal higher concentration of the smaller particles was found to be slightly pronounced for lower velocity. These analogies of particles are well discussed with the ratio between freeflight velocity and the gravitational settling velocity. Extended analytical model results were compared with the 3D computational fluid dynamics simulation results. Discrepancies in the model results were discussed.

Modeling Soluble and Particulate Lead Release into Drinking Water from Full and Partially Replaced Lead Service Lines

“…It can be shown that under modest turbulent flow regimes the behavior of a suspended particle as large as 44 μm (about 100 times the 0.45 μm threshold for particulate lead) will be dominated by turbulent diffusivity rather than inertia (Stk < 0.2). At such a low Stokes number, particles are expected to precisely follow the turbulent fluctuations of the flow stream, 37 can be modeled as a solute tracer. Therefore, the transport of mobilized particulate lead with the bulk flow is described by a 2-D convective-diffusion equation…”

“…It can be shown that under modest turbulent flow regimes the behavior of a suspended particle as large as 44 μm (about 100 times the 0.45 μm threshold for particulate lead) will be dominated by turbulent diffusivity rather than inertia (Stk < 0.2). At such a low Stokes number, particles are expected to precisely follow the turbulent fluctuations of the flow stream, and hence, their transport can be modeled as a solute tracer. Therefore, the transport of mobilized particulate lead with the bulk flow is described by a 2-D convective-diffusion equation where C p is the particulate lead concentration in the bulk flow (μg/L), D L,p and D r,p are the apparent diffusivities of particulate lead in the longitudinal and radial directions, respectively (cm 2 /s), and R set is the rate of particulate lead settling (μg/L/s).…”

Effects of Geometric Parameters for Wavy Finned-Tube Heat Exchanger in Turbulent Flow: A CFD Modeling

“…3D Navier-Stokes equations (Sohr 2012) were considered for the simulation of flow and heat transfer and energy equation for steady incompressible fluid with constant properties. The flow is described by the conservation laws for mass (continuity), momentum (Navier-Stokes) and by the energy equations are as follows (Hossain and Naser 2011, Bhuiyan and Naser 2014:…”