Effects of Pore Complex Shape, Distribution and Overlap on the Thermal Conductivity of Porous Insulation Materials
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Effects of Pore Complex Shape, Distribution and Overlap on the Thermal Conductivity of Porous Insulation Materials Xiaojian Wang1,2 · Xiaoxue Wang1 · Xiaohu Niu1 · Xiaowei Qiu1 · Liangbi Wang2 Received: 23 July 2020 / Accepted: 12 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
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. Keywords Pore complex shape · Pore distribution · Pore overlap · Porous material · Thermal conductivity Abbreviations a1 Length of side AB Left boundary of cell AD Top boundary of cell b1 Length of side BC Bottom boundary of cell * Xiaojian Wang [email protected] 1
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, Gansu, China
2
Key Laboratory of Railway Vehicle Thermal Engineering of Education Ministry, Lanzhou Jiaotong University, Lanzhou 730070, Gansu, China
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145
Page 2 of 21
International Journal of Thermophysics
(2020) 41:145
cp Specific heat (kJ·kg−1·K−1) c1 Length of side d1 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) Lx Length along the x axis Ly Height along the y axis n Normal direction N Number of pores q Heat flux (W·m−2) r Random number T Temperature (K) Tf Ambient temperature (K) V Volumetric fraction x, y Coordinates (m) x0 Coordinate of pore center (m) y0 Coordinate of pore center (m) Greek letters ρ Density (kg·m−3) β0 Directional angle (°) Subscripts c Porous material g Pore gas m Matrix material
1 Introduction Porous materials have been widely used in industrial applications such as heat exchanger, filter, building insulations, evaporator and so on [1–5]. In recent years, porous materials are raised in thermal managements and micro-electronics, where the performance of thermal insulation plays a very key role [6]. The the
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