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Technical Brief

Local Thermal Nonequilibrium During Melting of a Paraffin Filled in an Open-Cell Copper Foam: A Visualized Study at the Pore-Scale

[+] Author and Article Information
Li-Wu Fan

Mem. ASME
Institute of Thermal Science and Power Systems,
School of Energy Engineering,
Zhejiang University,
Hangzhou 310027, China;
State Key Laboratory of Clean Energy Utilization,
Zhejiang University,
Hangzhou 310027, China
e-mail: liwufan@zju.edu.cn

Hong-Qing Jin

Institute of Thermal Science and Power Systems,
School of Energy Engineering,
Zhejiang University,
Hangzhou 310027, China

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 4, 2016; final manuscript received October 10, 2016; published online December 7, 2016. Assoc. Editor: Guihua Tang.

J. Heat Transfer 139(3), 034505 (Dec 07, 2016) (6 pages) Paper No: HT-16-1252; doi: 10.1115/1.4035017 History: Received May 04, 2016; Revised October 10, 2016

In this technical brief, the application of infrared thermal imaging to investigate melting of a phase-change material (PCM) filled in an open-cell metal foam was proposed. Melting experiments in a rectangular cell were performed with paraffin/copper foam composite samples having a single pore size of 15 ppi. The visualized study at the pore-scale was enabled using an infrared video camera equipped with a macrolens, offering a resolution of 50 μm. The transient thermal imaging results were first validated against the temperature readings by a pre-installed thermocouple. A relative deviation below 4% was observed between the two methods over the entire course of melting. The local thermal nonequilibrium between a copper ligament and its surrounding paraffin was found to become more pronounced as melting proceeds, which could reach up to the order of 10 °C during the late stage of melting. The quantitative observation of the local thermal nonequilibrium effect may facilitate improvement of the existing two-temperature models for numerical simulations on melting of PCM enhanced by embedding metal foams.

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References

Figures

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Fig. 1

Photographs showing (a) the sample of a paraffin/copper foam composite, and (b) the rectangular drawer-type container for the composite PCM with two types of top plate, as well as schematic diagrams showing (c) the physical model of the melting process, and (d) the visualized experimental facility for melting of the composite PCM

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Fig. 2

DSC curves of the paraffin as determined at a constant heating/cooling rate of 5 °C/min

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Fig. 3

Comparison of local temperature variations measured by IR thermal imaging and a TC at the same location during melting of the composite PCM

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Fig. 4

The measured (a) local temperature variations by TCs, (b) local temperature difference evolutions by IR thermal imaging within a single pore, and (c) temperature contour evolutions at pore-scale by IR thermal imaging during melting of the composite PCM at a superheat of 20 °C

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Fig. 5

The measured (a) local temperature variations by TCs, (b) local temperature difference evolutions by IR thermal imaging within a single pore, and (c) temperature contour evolutions at pore-scale by IR thermal imaging during melting of the composite PCM at a superheat of 30 °C

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Fig. 6

The measured temperature profiles along the central line of the circular view window at representative time instants during melting of the composite PCM at a superheat of (a) 20 °C and (b) 30 °C

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