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Title:Use of Lagrangian methods to describe particle deposition and distribution in dispersed flows
Author(s):Binder, Jeffrey Louis
Doctoral Committee Chair(s):Hanratty, Thomas J.
Department / Program:Nuclear Engineering
Discipline:Nuclear Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Chemical
Engineering, Mechanical
Engineering, Nuclear
Abstract:Experimental studies of the interchange processes in vertical gas-liquid annular flow by Leman (1985) and Schadel (1988) in this laboratory have been completed. This work defines the effect of pipe diameter, gas and liquid flow rates on deposition rates in air-water annular flow. An estimate of the droplet slip ratios has been obtained. This provides an improved correlation of measured deposition rates with droplet concentration. In addition droplet slip ratios are useful for correctly estimating the role of the droplets on the two phase pressure drop.
An experimental test section has been developed to photograph the dispersed phase in vertical annular flow. The test section allows for end view or side view photographs to be taken. These photographs can provide information on drop size, concentration and velocity.
Lagrangian methods have been developed in order to predict particle deposition and distribution in turbulent dispersed flows. The theoretical description developed here is restricted to dilute concentrations and particles with length scales of motion large compared to length scales characterizing non-homogeneities in the flow field. The method focuses on describing the behavior of instantaneous sources. Time dependent turbulent diffusion is considered. Fully developed fields are obtained from an appropriate distribution of ring sources. Specific applications have been made to gas-liquid annular flows and sediment transport.
Application of the Lagrangian model to vertical annular flow provides an interpretation of measured deposition rates and concentration distributions that previously were not understood. Particle deposition constants are found to depend on one dimensionless parameter, $\beta\tau\sb{\rm Lf}$, that measures the ability of the particle to follow the gas phase turbulence.
The model developed for vertical flows is extended to horizontal annular flows. Deposition is viewed to occur from two mechanisms operating in parallel. The first is due to the turbulence and second is due to gravitational settling. Particle deposition and concentration are found to depend on $\beta\tau\sb{\rm Lf}$ and a Froude number which measures the effect of gravitational settling on the particle.
The model is useful for describing deposition measurements in gas-liquid annular flows in channels. The product of $\beta\tau\sb{\rm Lf}$ and the Froude number is found to define transitions from stratified, asymmetric and symmetric flow regimes.
The model is also extended to describe sediment transport in channels. A situation is considered where the sand is viewed to enter the flow field from an erodible bed of sediment on the bottom of the channel. Eulerian models that have considered entrainment to be due to the turbulence and deposition to be due to settling have required using particle diffusivities larger than the fluid. This is explained by considering time dependent effects on the diffusion and settling velocities.
Issue Date:1991
Rights Information:Copyright 1991 Binder, Jeffrey Louis
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9136546
OCLC Identifier:(UMI)AAI9136546

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