UVM Theses and Dissertations
Format:
Print
Author:
Hewitt, Gregory Frank Sutton
Dept./Program:
Mechanical Engineering
Year:
2010
Degree:
MS
Abstract:
A computational study is performed of the transport of a particulate suspension through a corrugated tube using a discrete-element method. The tube is axisymmetric with a radius that varies sinusoidally along the tube length, which in the presence of a mean suspension flow leads to periodic inward and outward acceleration of the advected particles. The oscillations in radial acceleration and straining rate lead to a net radial drift, with mean acceleration measuring about an order of magnitude smaller than the instantaneous radial acceleration, which over time focuses small particles within the tube. The foundations of particle focusing in this flow are examined analytically using lubrication theory together with a low Stokes-number approximation for the particle drift. This lubrication theory solution provides the basic scaling for how the particle drift will vary with wave amplitude and wavelength. Computations are then performed using a finite-volume method for fluid flow in the tube at higher Reynolds numbers over a range of amplitudes, wavelengths and Reynolds numbers, examining the effect of each of these variables on the averaged radial fluid acceleration.
A discrete element method (OEM) is used to simulate particle behavior at finite Stokes numbers, and the results are compared to an asymptotic approximation for low Stokes numbers. At low tube Reynolds number (e.g., Re = 10), the drift velocity induced by the tube corrugations focuses the particles onto the tube centerline, in accordance with the low Stokes number approximation based on the axial averaged fluid radial acceleration. At higher tube Reynolds numbers (e.g., Re = 100), the correlation between the particle radial oscillation and the fluid acceleration field leads the outermost particles to drift into a ring at a finite radius from the tube center, with little net motion of the particles in the innermost part of the tube. At larger Stokes numbers, particles can be dispersed to the outer regions of the tube due to particle outward dispersion from the large instantaneous radial acceleration. The effects of eddy formation within the corrugation crests on particle focusing is also examined.
A discrete element method (OEM) is used to simulate particle behavior at finite Stokes numbers, and the results are compared to an asymptotic approximation for low Stokes numbers. At low tube Reynolds number (e.g., Re = 10), the drift velocity induced by the tube corrugations focuses the particles onto the tube centerline, in accordance with the low Stokes number approximation based on the axial averaged fluid radial acceleration. At higher tube Reynolds numbers (e.g., Re = 100), the correlation between the particle radial oscillation and the fluid acceleration field leads the outermost particles to drift into a ring at a finite radius from the tube center, with little net motion of the particles in the innermost part of the tube. At larger Stokes numbers, particles can be dispersed to the outer regions of the tube due to particle outward dispersion from the large instantaneous radial acceleration. The effects of eddy formation within the corrugation crests on particle focusing is also examined.