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Research Papers

Shear Induced Removal of Calcium Carbonate Scale From Polypropylene and Copper Tubes

[+] Author and Article Information
Matt Royer, Susan C. Mantell

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455

Jane H. Davidson1

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455

Lorraine F. Francis

Department of Chemical Engineering and Material Science, University of Minnesota, Minneapolis, MN 55455

1

Corresponding author.

J. Sol. Energy Eng 132(1), 011013 (Jan 04, 2010) (9 pages) doi:10.1115/1.4000573 History: Received August 09, 2009; Revised September 16, 2009; Published January 04, 2010

This paper presents an analytical model and an experimental study of adhesion and fluid shear removal of calcium carbonate scale on polypropylene and copper tubes in laminar and turbulent water flows, with a view toward understanding how scale can be controlled in solar absorbers and heat exchangers. The tubes are first coated with scale and then inserted in a flow-through apparatus. Removal is measured gravimetrically for Reynolds numbers from 525 to 5550, corresponding to wall shear stresses from 0.16 Pa to 6.0 Pa. The evolutionary structure of the scale is visualized with scanning electron microscopy. Consistent with the predictive model, calcium carbonate is more easily removed from polypropylene than copper. In a laminar flow with a wall shear stress of 0.16 Pa, 65% of the scale is removed from polypropylene while only 10% is removed from copper. Appreciable removal of scale from copper requires higher shear stresses. At Reynolds number of 5500, corresponding to a wall shear stress of 6.0 Pa, 30% of the scale is removed from the copper tubes. The results indicate scale will be more easily removed from polypropylene, and by inference other polymeric materials, than from copper by flushing with water.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Forces acting on a deposited particle subjected to fluid flow (from Ref. 18)

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Figure 2

Adhesion force distribution for calcite particles deposited on PP, Cu, and CuO

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Figure 3

Critical local velocities as a function of particle diameter

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Figure 4

Critical shear stress as a function of particle diameter

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Figure 5

Particle size distribution in calcite slurry

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Figure 6

Schematic of flow-through system (not to scale)

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Figure 7

Percentage of scale removed versus shear stress after 5 min in laminar flow for polypropylene (◻) and copper (△) tubes

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Figure 8

SEM images shown at 2500 times for (a) the initial scale layer deposited on a clean PP tube and PP tubes after 5 min exposure to shear stresses of (b) 0.16 Pa, (c) 0.22 Pa, (d) 0.31 Pa, and (e) 0.38 Pa

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Figure 9

SEM images at 2500 for (a) the initial scale layer deposited on a Cu tube and Cu tubes after a 5 min exposure to shear stresses of (b) 0.16 Pa, (c) 0.22 Pa, (d) 0.31 Pa, (e) 0.38 Pa, and (f) 6.0 Pa

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Figure 10

Percentage of scale removed from copper tubes versus shear stress after 5 min in turbulent flow

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Figure 11

Comparison of predicted and measured shear removal

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