Concentration Variations and Their Effects in Flowing Slurries and Emulsions
Date
1992-02
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Degree Level
Doctoral
Abstract
Two aspects of two-phase pipe flow were investigated in this study: the concentration fluctuations which occur during flow and the inward migration of the particles or droplets which form the dispersed phase.
The concentration fluctuation spectrum study was undertaken to better understand slurry flow. In this investigation, local concentration fluctuations were measured indirectly with a conductivity probe. Slurry and flow parameters were varied to determine their influence on the fluctuation spectrum. The concentration fluctuation spectra, particularly those of turbulent flow, resembled turbulent energy spectra obtained with single phase flows by previous investigators. However, the concentration fluctuation spectra decayed at lower wavenumbers than the single phase turbulent energy spectra. The particle diameter or the sensor spacing could account for this difference.
Inward particle or droplet migration has been observed in previous slurry flow studies and has been associated with lower pipeline friction losses. In this investigation a systematic study of the concentration distribution of particles in vertical pipeline flow was undertaken. An attempt was made to interpret these results with a dispersive stress model using a multiple regression correlation. Unfortunately, the best correlation was found to be incapable of predicting the concentration profile accurately. However the experiment did establish the qualitative effect of
particle diameter and density, pipe diameter, bulk concentration, and bulk velocity on inward migration. It is believed that more than one mechanism may be responsible for the inward acting force.
An oil -in-water emulsion pipeline flow investigation was then undertaken to determine both the extent of inward migration of oil droplets and its influence on the pipeline friction loss. In this investigation, techniques to measure the velocity distribution, concentration distribution, and size distribution of oil droplets were employed for the first time. The droplets were found to be uniformly distributed over the pipe cross-section so that two-phase homogeneous models predicted the friction losses accurately. Although the dispersive stress model did not predict the concentration distribution satisfactorily for the emulsions, these experimental results were in qualitative agreement with the vertical flow experiments.
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Degree
Doctor of Philosophy (Ph.D.)
Department
Chemical Engineering
Program
Chemical Engineering