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TECHNICAL PAPERS

Scaling in Polymer Tubes and Interpretation for Use in Solar Water Heating Systems

[+] Author and Article Information
Yana Wang, Jane Davidson, Lorraine Francis

University of Minnesota, 111 Church St., S.E., Minneapolis, MN 55455

J. Sol. Energy Eng 127(1), 3-14 (Feb 07, 2005) (12 pages) doi:10.1115/1.1823492 History: Received May 17, 2004; Revised June 22, 2004; Online February 07, 2005
Copyright © 2005 by ASME
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References

Figures

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Experimental apparatus to monitor the growth of calcium carbonate on polymer and copper tubes placed in tube-in-shell heat exchangers
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Predicted temperatures in the streamwise direction along the length of each tube: (a) bulk water temperature, (b) interior surface temperature
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Predicted supersaturation ratio (S) of hard water as a function of bulk fluid temperature for water initially prepared at 10°C with [Ca2+]t=4×10−3 M (400 ppm CaCO3), and pH=9
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SEM images of nylon 6,6 tubes: (a) ×25,000, native; (b) ×500; and (c) ×25,000, after 540 h exposure to 1200 L supersaturated water (S≈8) in a tube-in-shell heat exchanger
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SEM images of HTN tubes: (a) ×25,000, native; (b) ×500; and (c) ×25,000, after 540 h exposure to 2500 L supersaturated water (S≈8) in a tube-in-shell heat exchanger
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SEM images of PB tubes: (a) ×25,000, native; (b) ×500; and (c) ×25,000 after 540 h exposure to 500 L supersaturated water (S≈8) in a tube-in-shell heat exchanger
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SEM images of PP tubes: (a) ×25,000, native; (b) ×500; and (c) ×25,000, after 540 h exposure to 300 L supersaturated water (S≈8) in a tube-in-shell heat exchanger
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SEM images of Teflon tubes: (a) ×25,000, native; (b) ×500; and (c) ×25,000, after 540 hours exposure to 330 L supersaturated water (S≈8) in a tube-in-shell heat exchanger
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SEM images of copper tubes: (a) ×25,000, native; (b) ×500; and (c) ×25,000, after 540 h exposure to 1500 L supersaturated water (S≈8) in a tube-in-shell heat exchanger
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SEM images of interior surface of nylon 6,6 tube in heat exchanger 2 after 330 h exposure to 724 L supersaturated water (S≈8) in a tube-in-shell heat exchanger: (a) secondary electron image, 25,000×; (b) backscattered electron image, 25,000×
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XRD spectra (I) before and (II) after 540 h exposure to supersaturated water: (a) nylon 6,6; (b) HTN; (c) PB; (d) PP; (e) Teflon; (f ) copper. The asterisks indicate peaks associated with either calcite or aragonite.
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CaCO3 per unit surface area versus time (⋄ ) nylon 6,6, ×HTN,+PB, (□ ) PP, (▵ ) Teflon, and (⎔ ) copper; (a) tubes in heat exchanger 1, (b) tubes in heat exchanger 2. These data were determined using 3-cm long sections of tube removed during the experiment. Measurement uncertainty is 0.01 g/m2.
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Measured scaling rates based on mass of CaCO3 per surface area exposed to flowing water. Data for tubes in heat exchangers 1, 2, and 3 are based on analysis of 15-cm long sections removed at the end of the 540 h accelerated phase. Measurement uncertainty is 1×10−8 g/m2 s.
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Comparison of measured and predicted scaling rates. The measured rate is an average of the scaling rates shown in Fig. 13.

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