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Effects of Pore Complex Shape, Distribution and Overlap on the Thermal Conductivity of Porous Insulation Materials

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Abstract

The effective thermal conductivity of porous materials is determined by many factors. Previous works were mainly focused on the pore content and the thermal conductivity of two components. However, few researches pay attention to the effects of pore complex shape, overlap and distribution. In this study, the effects of pore complex shape, distribution and overlap are investigated at the same time. It is found that the best pore should have relatively larger contact areas in the direction vertical to heat flux. I-shaped and T-shaped pores have the larger contact area in any type of the pore distributions. They have the most impact on the thermal conductivity of the porous material. I-shape pore with directional distribution is better than random distribution. The rhombic, elliptical and rectangular pores have larger thermal insulation in random distribution than in directional distribution. The efficiency of square, triangular and T-shaped pores are similar in directional and random distributions. The pore overlap only has the apparent effect on the I-shaped pore. New methods to control the distribution and overlapped direction of pores should be investigated in the future.

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Abbreviations

a 1 :

Length of side

AB :

Left boundary of cell

AD :

Top boundary of cell

b 1 :

Length of side

BC :

Bottom boundary of cell

c p :

Specific heat (kJ·kg−1·K−1)

c 1 :

Length of side

d 1 :

Length of side

DC :

Right boundary of cell

h :

Convective heat transfer coefficient (W·m−2·K−1)

K :

Thermal conductivity (W·m−1·K−1)

L x :

Length along the x axis

L y :

Height along the y axis

n :

Normal direction

N :

Number of pores

q :

Heat flux (W·m−2)

r :

Random number

T :

Temperature (K)

T f :

Ambient temperature (K)

V :

Volumetric fraction

x, y :

Coordinates (m)

x 0 :

Coordinate of pore center (m)

y 0 :

Coordinate of pore center (m)

ρ :

Density (kg·m−3)

β 0 :

Directional angle (°)

c:

Porous material

g:

Pore gas

m:

Matrix material

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Acknowledgments

This Project is supported by the Foundation of A Hundred Youth Talents Training Program of Lanzhou Jiaotong University. It is also supported by the National Natural Science Foundation of China, No. 51406072.

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Authors and Affiliations

  1. School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, Gansu, China

    Xiaojian Wang, Xiaoxue Wang, Xiaohu Niu & Xiaowei Qiu

  2. Key Laboratory of Railway Vehicle Thermal Engineering of Education Ministry, Lanzhou Jiaotong University, Lanzhou, 730070, Gansu, China

    Xiaojian Wang & Liangbi Wang

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  1. Xiaojian Wang
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  2. Xiaoxue Wang
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Correspondence to Xiaojian Wang.

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Wang, X., Wang, X., Niu, X. et al. Effects of Pore Complex Shape, Distribution and Overlap on the Thermal Conductivity of Porous Insulation Materials. Int J Thermophys 41, 145 (2020). https://doi.org/10.1007/s10765-020-02730-8

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