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Research Papers

Heat Conduction of a Porous Material

[+] Author and Article Information
Koji Miyazaki1

Department of Mechanical and Control Engineering,  Kyushu Institute of Technology, Kitakyushu, Fukuoka 804-8550, Japanmiyazaki@mech.kyutech.ac.jp

Saburo Tanaka, Daisuke Nagai

Department of Biological Functions and System Engineering,  Kyushu Institute of Technology, Kitakyushu, Fukuoka 808-0196, Japan

1

Corresponding author.

J. Heat Transfer 134(5), 051018 (Apr 13, 2012) (7 pages) doi:10.1115/1.4005709 History: Received July 26, 2010; Revised August 12, 2011; Published April 11, 2012; Online April 13, 2012

In this study, we introduce our numerical and experimental works for the thermal conductivity reduction by using a porous material. Recently thermal conductivity reduction has been one of the key technologies to enhance the figure of merit (ZT) of a thermoelectric material. We carry out numerical calculations of heat conduction in porous materials, such as phonon Boltzmann transport (BTE) and molecular dynamics (MD) simulations, in order to investigate the mechanism of the thermal conductivity reduction of a porous material. In the BTE, we applied the periodic boundary conditions with constant heat flux to calculate the effective thermal conductivity of porous materials.In the MD simulation, we calculated the phonon properties of Si by using the Stillinger–Weber potential at constant temperature with periodic boundary conditions in the x, y, and z directions. Phonon dispersion curves of single crystal of Si calculated from MD results by time-space 2D FFT are agreed well with reference data. Moreover, the effects of nanoporous structures on both the phonon group velocity and the phonon density of states (DOS) are discussed. At last, we made a porous p-type Bi2 Te3 by nanoparticles prepared by a beads milling method. The thermal conductivity is one-fifth of that of a bulk material as well as keeping the same Seebeck coefficient as the bulk value. However, electrical conductivity was much reduced, and the ZT was only 0.048.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of the coordinate system showing the phonon intensity and the various angles of interest

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Figure 2

Schematic diagram of phonon transport model for heat conduction in a porous material

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Figure 3

Nondimensional effective temperature distributions of nanoporous materials: (a) Kn = 0.1 and (b) Kn = 5

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Figure 4

Effective thermal conductivities of nanoporous materials under various Knudsen numbers. Solid lines are the maximum and minimum values estimated by conventional simple model.

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Figure 5

MD simulation models for phonon calculations: (a) Single Si crystal; (b) Si with nanoholes at intervals of 2a; and (c) Si with nanoholes at random

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Figure 6

Phonon dispersion relations of Si in (001) obtained by time-space FFT: (a) Longitudinal; (b) and (c) transverse

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Figure 9

Nanoporous p-type Bismuth telluride: (a) Bulk disk samples and (b) AFM images of surface morphology of the sample

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Figure 7

Longitudinal phonon dispersion curves of (a) Si, and nanostructured Si with (b) periodic nanopores, and (c) random nanopores

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Figure 8

Density of states of phonon: (a) Si crystal and (b) Si with periodic nanoholes

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