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Research Papers

Improved Thermal Response in Encapsulated Phase Change Materials by Nanotube Attachment on Encapsulating Solid

[+] Author and Article Information
I. T. Barney, S. M. Mukhopadhyay

Center for Nanoscale Multifunctional Materials,
Department of Mechanical and
Materials Engineering,
Wright State University,
3640 Colonel Glenn Highway,
Dayton, OH 45435

A. K. Roy

Thermal Sciences & Materials Branch,
Air Force Research Laboratory,
AFRL/RXBT Bldg 654,
2941 Hobson Way,
WPAFB, OH 45433-7750

Manuscript received April 11, 2012; final manuscript received July 30, 2012; published online January 18, 2013. Assoc. Editor: Debjyoti Banerjee.

J. Nanotechnol. Eng. Med 3(3), 031005 (Jan 18, 2013) (6 pages) doi:10.1115/1.4007327 History: Received April 11, 2012; Revised July 30, 2012

This paper demonstrates greatly improved specific power (W/g) for encapsulated phase change materials (EPCM) as a result of modified interface morphology. Carbon nanotubes are strongly attached to the interior walls of the graphitic foam encapsulation. Microstructure analysis using scanning electron microscopy (SEM) indicates that the wax infiltrates into the carbon nanotubes (CNT) forest and creates an intimate contact with increased interfacial area between the two phases. Specific power has been calculated by measuring thermal response times of the phase change materials using a custom system. The carbon nanotubes increase the specific power of the encapsulated phase change materials by about 27% during heating and over 146% during the more important stage of latent heat storage. Moreover, SEM images of the interface after repeated thermal cycling indicate that the presence of CNT may also improve durability of the EPCM by preventing interfacial gaps and maintaining improved contact between the graphite and PCM phases.

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Figures

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Fig. 1

Thermal testing apparatus designed and built at Air Force Research Laboratory. The Cu cylinder is heated with 10 W from below. The input temperature is measured with TC1. The thermal response of the sample is measured with TC2.

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Fig. 2

Pore structure of the multicellular graphitic foam encapsulation material

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Fig. 3

Surface of a pore wall in the multicellular foam showing graphitic planes perpendicular to the interface

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Fig. 4

Carbon nanotubes grown over the multicellular graphitic foam. Aligned snakes of carbon nanotubes can be seen extending into the pores.

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Fig. 5

Spaghetti like distribution of randomly oriented carbon nanotubes attached to the surface of the multicellular graphitic foam

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Fig. 6

Paraffin wax is found to penetrate the nanotubes all the way to the silica interface

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Fig. 7

Average specific power at 10 W input during heating and during storage of latent heat for the multicellular encapsulation without CNT (light gray = MGfoam) and with CNT (dark gray = CNTfoam). Error bars represent the full range of measurements.

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Fig. 8

Nano fissure along interface of multicellular graphitic foam (bottom region) with paraffin wax PCM (top region)

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Fig. 9

Interface of CNTfoam3 showing graphite (bottom), CNT and wax (middle-bright lines), and the paraffin wax beyond (top). Second blurry line of silica and CNT are from a shifted sheet of the graphite in the foreground.

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