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Research Papers: Micro/Nanoscale Heat Transfer

Heat Transfer During Constrained Melting of Nano-Enhanced Phase Change Materials in a Spherical Capsule: An Experimental Study

[+] 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

Zi-Qin Zhu, Min-Jie Liu, Can-Ling Xu

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

Yi Zeng

Department of Mechanical Engineering,
Auburn University,
Auburn, AL 36849

Hai Lu

Electric Power Research Institute,
Yunnan Electric Power
and Research Institute (Group),
Kunming, Yunnan 650217, China

Zi-Tao Yu

Institute of Thermal Science and Power Systems,
School of Energy Engineering,
Zhejiang University,
Hangzhou 310027, China;
Key Laboratory of Refrigeration and Cryogenic
Technology of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 5, 2016; final manuscript received July 2, 2016; published online August 16, 2016. Assoc. Editor: Amy Fleischer.

J. Heat Transfer 138(12), 122402 (Aug 16, 2016) (9 pages) Paper No: HT-16-1055; doi: 10.1115/1.4034163 History: Received February 05, 2016; Revised July 02, 2016

The classical problem of constrained melting heat transfer of a phase change material (PCM) inside a spherical capsule was revisited experimentally in the presence of nanoscale thermal conductivity fillers. The model nano-enhanced PCM (NePCM) samples were prepared by dispersing self-synthesized graphite nanosheets (GNSs) into 1-dodecanol at various loadings up to 1% by mass. The melting experiments were carried out using an indirect method by measuring the instantaneous volume expansion upon melting. The data analysis was performed based on the homogeneous, single-component assumption for NePCM with modified thermophysical properties. It was shown that the introduction of nanofillers increases the effective thermal conductivity of NePCM, in accompaniment with an undesirable rise in viscosity. The dramatic viscosity growth, up to over 100-fold at the highest loading, deteriorates significantly the intensity of natural convection, which was identified as the dominant mode of heat transfer during constrained melting. The loss in natural convection was found to overweigh the decent enhancement in heat conduction, thus resulting in decelerated melting in the presence of nanofillers. Except for the case with the lowest heating boundary temperature, a monotonous slowing trend of melting was observed with increasing the loading.

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Figures

Grahic Jump Location
Fig. 1

Schematic diagram of the experimental setup for studying constrained melting in a spherical capsule by the volume expansion scheme

Grahic Jump Location
Fig. 4

Variations of the melt fraction as correlated to a combination of scaled dimensionless groupings for the (a) 0.0 wt.%, (b) 0.5 wt.%, and (c) 1.0 wt.% NePCM samples, and for (d) nine select cases together

Grahic Jump Location
Fig. 5

Transient variations of the surface-averaged Nu number during constrained melting of the various NePCM samples at the boundary temperature of (a) 26 °C, (b) 35 °C, (c) 45 °C, and (d) 55 °C

Grahic Jump Location
Fig. 2

Transient temperature variations during constrained melting for the (a) 0.0 wt.%, (b) 0.5 wt.%, and (c) 1.0 wt.% NePCM samples as measured at positions along the central line inside the spherical capsule at the boundary temperature of 55 °C

Grahic Jump Location
Fig. 3

Transient variations of the melt fraction during constrained melting of the various NePCM samples at the boundary temperature of (a) 26 °C, (b) 35 °C, (c) 45 °C, and (d) 55 °C

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