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Research Papers: Melting and Solidification

Heat Transfer and Thermodynamic Analyses of Some Typical Encapsulated Ice Geometries During Discharging Process

[+] Author and Article Information
David MacPhee1

Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canadadavid.macphee@uoit.ca

Ibrahim Dincer

Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canadaibrahim.dincer@uoit.ca

1

Corresponding author.

J. Heat Transfer 131(8), 082301 (Jun 05, 2009) (15 pages) doi:10.1115/1.3111262 History: Received October 16, 2008; Revised January 13, 2009; Published June 05, 2009

This study deals with the process of melting in some typical encapsulated ice thermal energy storage (TES) geometries. Cylindrical and slab capsules are compared with spherical capsules when subjected to a flowing heat transfer fluid (HTF). The effect of inlet HTF temperature and flow rate as well as the reference temperatures are investigated, and the resulting solidification and melting times, energy efficiencies, and exergy efficiencies are documented. Using ANSYS GAMBIT and FLUENT 6.0 softwares, all geometries are created, and the appropriate boundary and initial conditions are selected for the finite volume solver to proceed. Sufficient flow parameters are monitored during transient solutions to enable the calculation of all energy and exergy efficiencies. The energetically most efficient geometric scenario is obtained for the slab geometry, while the spherical geometry exergetically achieves the highest efficiencies. The difference between the two results is mainly through the accounting of entropy generation and exergy destroyed, and the largest mode of thermal exergy loss is found to be through entropy generation resulting from heat transfer accompanying phase change, although viscous dissipation is included in the analysis. All efficiency values tend to increase with decreasing HTF flow rate, but exergetically the best scenario appears to be for the spherical capsules with low inlet HTF temperature. Energy efficiency values are all well over 99%, while the exergy efficiency values range from around 72% to 84%, respectively. The results indicate that energy analyses, while able to predict viscous dissipation losses effectively, cannot correctly quantify losses inherent in cold TES systems, and in some instances predict higher than normal efficiencies and inaccurate optimal parameters when compared with exergy analyses.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Storage tank schematic for (a) cylindrical capsules, (b) spherical capsules, and (c) slab capsules

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Figure 2

Auxiliary (a), front (b), and side (c) views of the spherical capsule domain

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Figure 3

Auxiliary (a), front (b), and side (c) views of the cylindrical capsule domain

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Figure 4

Auxiliary (a), front (b), and side (c) views of the rectangular prism (slab) capsule domain

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Figure 5

Numerical and experimental temperature profiles at the front of the sphere (θ=0 deg)

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Figure 6

Numerical and experimental temperature profiles at the side of the sphere (θ=90 deg)

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Figure 7

Numerical and experimental temperature profiles at the back of the sphere (θ=180 deg)

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Figure 8

Normalized energy efficiency values (in percent) for flow rates of (a) Q1=8.7×10−4 m3/s, (b) Q2=1.74×10−3 m3/s, and (c) Q3=2.61×10−3 m3/s

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Figure 9

Exergy efficiency values (in percent) for flow rates of (a) Q1=8.7×10−4 m3/s, (b) Q2=1.74×10−3 m3/s, and (c) Q3=2.61×10−3 m3/s

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Figure 10

Effect of dead-state temperature on exergy and normalized energy efficiencies for the spherical geometry with a flow rate of Q3=2.61×10−3 m3/s

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Figure 11

Exergy destruction with respect to the dead-state temperature; the spherical geometry with a flow rate of Q3=2.61×10−3 m3/s is shown

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Figure 12

Exergy destroyed contents for the cylindrical geometry, experiencing a flow rate of Q3=2.61×10−3 m3/s in a bed of 1000 or 5000 capsules.

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