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Research Papers

Effect of Near-Wall Turbulence on Selective Removal of Particles From Sand Beds Deposited in Pipelines

[+] Author and Article Information
Hossein Zeinali1

School of Mining and Petroleum Engineering, Natural Resources Engineering Facility,  University of Alberta, Edmonton, AB, T6G 2W2, Canadazeinali@ualberta.ca

Peter Toma, Ergun Kuru

School of Mining and Petroleum Engineering, Natural Resources Engineering Facility,  University of Alberta, Edmonton, AB, T6G 2W2, Canada

1

Corresponding author.

J. Energy Resour. Technol 134(2), 021003 (Apr 04, 2012) (9 pages) doi:10.1115/1.4006041 History: Received May 17, 2010; Revised January 19, 2012; Published April 02, 2012; Online April 04, 2012

This paper investigates the effect of near-wall turbulence on selective removal of small-size particulate matter from sand beds deposited in pipelines. In an effort to develop effective strategies for in-line fines separation, experimental data on selective particle removal by burst-sweep turbulent structures have been gathered. A 3¾″ (0.095 m) diameter—15 m long flow loop together with a particle image velocimetry (PIV) system has been commissioned and used for observations of turbulent burst activities. The flow loop was also equipped with bottom extractors to allow real time sampling of deposited particles which are then analyzed for determining particle size distribution changes with time. In this work, the alteration of size-composition during turbulent transportation of moving (sand) bed was assumed to be the effect of burst-sweep activity (coherent structures). The frequency of coherent burst structures was measured at various distances from the pipe wall, during the radial dissipation, and results were compared with existing literature. The experimental results indicated that when a bed of particles with 0.1–50 μm size range is exposed to burst-sweep activities during turbulent pipe flow, the concentration of fine particles within the bed increases with time (i.e., coarser particles are preferentially removed).

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 7

Main components of experimental rig

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Figure 8

Near-wall burst initiation and dissipation snapshot obtained by processing the PIV data (average flow velocity 0.19 m/s)

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Figure 9

PIV measured burst frequency (#burst/100 s) assessed at four levels in the boundary layer and the frequency calculated (at Z1) using “Cleaver and Yates” (C&Y) method [9]

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Figure 10

Schematic illustration of burst evolving from pipe wall to turbulent core flow [18]

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Figure 11

Concentration shift between transported sand bed and slurry (initial sand mixture of dp  > 50 μm—superficial slurry velocity of 0.33 m/s—Re = 27,899; LD bed sample was taken 135 min after the start of the experiment)

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Figure 12

Change of particle size distribution in the moving lenticular bed deposits with time (dp  < 60 μm, slurry flow velocity is 0.33 m/s; LD bed sample was taken 135 min after the start of the experiment)

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Figure 13

Change of particle size distribution in the moving lenticular bed deposits with time (dp  < 60 μm, slurry flow velocity is 0.36 m/s)

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Figure 1

Idealization of burst-sweep activity from sand bed emerging from near-wall to core turbulent flow [9]

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Figure 2

(a) Simultaneous record of local velocity components U and V versus time; (b) burst and sweep assessment performed by comparing the signs of fluctuating velocity components u′ and v′ —the four-quadrant method [5]

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Figure 3

Two distinct critical particle entrainment regimes as function of the wall shear stress and size range found in the bed [14] (silica sand–water)

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Figure 4

Main forces considered for removal and grading of particles from a sand bed during slurry transportation

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Figure 5

Attraction and buoyant forces contributing to particle removal (silica sand–water)

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Figure 6

Entraining forces acting on particles exposed to turbulent core flow (calculation is done for silica sand slurry at Uavg  = 0.36 m/s, Re = 27,660)

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