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Research Papers

Optimization of a Phase Change Thermal Storage Unit

[+] Author and Article Information
Monica F. Bonadies

 Center for Advanced Turbines and Energy Research, University of Central Florida, 4000 Central Florida Boulevard, Building 40, Room 307 Orlando, FL 32816Monica.Bonadies@gmail.com

Mark Ricklick

 Center for Advanced Turbines and Energy Research, University of Central Florida, 4000 Central Florida Boulevard, Building 40, Room 307 Orlando, FL 32816mricklick@gmail.com

J. S. Kapat

 Center for Advanced Turbines and Energy Research, University of Central Florida, 4000 Central Florida Boulevard, Building 40, Room 307 Orlando, FL 32816Jayanta.Kapat@ucf.edu

J. Thermal Sci. Eng. Appl 4(1), 011007 (Mar 19, 2012) (9 pages) doi:10.1115/1.4005209 History: Received February 14, 2011; Revised August 13, 2011; Published March 09, 2012; Online March 19, 2012

Several options exist to collect thermal energy from the sun for domestic use. This study examines a system integrating evacuated tube collectors with heat pipes with a storage unit using melted paraffin wax to store thermal energy. A shell-and-tube heat exchanger is embedded within the paraffin wax storage with a volume of 0.23 m3 . The heat exchanger includes two loops: one for glycol to transfer heat to the paraffin and one for water to extract heat from the melted paraffin. Although the paraffin has the benefit of being inexpensive and nontoxic, it has low thermal conductivity. Therefore, the heat exchanger has large brazed copper fins to extend areas of high thermal conductivity into the wax reservoir. To determine the benefit of the fins, wax and working fluid temperature data are taken from a constructed thermal energy storage unit and then used to verify a finite-difference one-dimensional analytical model of the unit. The maximum operating temperature of the glycol/water mix heat transfer fluid was approximately 65 °C when the fluid flowed at 3.78 l/min. City water at approximately 11.34 l/min was used to test the water heating capabilities of the unit. The one dimensional model proved useful in predicting the heat storage mode of the system. Due to its form, which was specifically developed for the unit in the study, the model could be adjusted to calculate thermal performance of similarly constructed thermal storage units.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Interior of evacuated solar thermal collection heat pipe (side view)

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Figure 2

Interior of evacuated solar thermal collection heat pipe (top view)

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Figure 3

Average family electricity use

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Figure 4

Fin and wall energy balance—melting case

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Figure 5

Analytical model regions

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Figure 6

Fin and wall energy balance—freezing case

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Figure 7

Solar thermal collection and storage system

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Figure 8

Solar thermal collection system assembly

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Figure 9

Model of internal heat exchanger

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Figure 10

Side view of thermal storage unit

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Figure 11

Top view of storage unit

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Figure 12

Semi-infinite solid approximation

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Figure 13

Control volume types

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Figure 14

Heat collection results

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Figure 15

Heat release results

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Figure 16

Melting resistance results at first fin location

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Figure 17

Comparison of simulated and actual melting and freezing processes, January 2010

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