Study on pore size distribution and thermal conductivity of aramid nanofiber aerogels based on fractal theory

2021 ◽  
Vol 130 (22) ◽  
pp. 225104
Author(s):  
Xiao Chen ◽  
Yinghe Hu ◽  
Xupin Zhuang ◽  
Xiaoyin Wang
Keyword(s):  
Thermal Conductivity ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Fractal Theory

Thermal Conductivity of Sol-Gel Bonded Castables

2008 ◽  
Vol 368-372 ◽  
pp. 1146-1148
Author(s):  
Feng Cao ◽  
C.Y. Wang ◽  
P.S. Tang ◽  
C.Y. Lu ◽  
H.F. Chen ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Glassy Phase ◽  
Size Structure ◽  
Sol Gel ◽  
Refractory Castables ◽  
Silica Alumina ◽  
Alumina Sol

The silica-alumina sol bonding agent, prepared by the sol gel route from ethyl silicate and aluminium isopropanol, was utilized in the refractory castables. The influence of structure on the heat transfer has been investigated using different sorts of refractory matrix. The results indicated that the heat conductivity of sol-gel bonded castables was considerably affected by their structure. The phase composition of matrix, porosity, pore size distribution and pore size structure were the most important factors. Thermal conductivity has been measured from the ambient temperature up to 1250 °C. The influence of crystalline phases and the glassy phase formation and the influence of the pore size distribution on the thermal conductivity were also described in this work.

Pore Size Distribution and Apparent Gas Thermal Conductivity of Silica Aerogel

1994 ◽  
Vol 116 (3) ◽  
pp. 756-759 ◽  
Author(s):  
S. Q. Zeng ◽  
A. J. Hunt ◽  
W. Cao ◽  
R. Greif
Keyword(s):  
Thermal Conductivity ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Silica Aerogel

scholarly journals A Fractal Model of Hydraulic Conductivity for Saturated Frozen Soil

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 369 ◽  
Author(s):  
Lei Chen ◽  
Dongqing Li ◽  
Feng Ming ◽  
Xiangyang Shi ◽  
Xin Chen
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Fractal Theory ◽  
Frozen Soil ◽  
Soil Freezing ◽  
Size Dimension ◽  
Maximum Pore Size

In cold regions, hydraulic conductivity is a critical parameter for determining the water flow in frozen soil. Previous studies have shown that hydraulic conductivity hinges on the pore structure, which is often depicted as the pore size and porosity. However, these two parameters do not sufficiently represent the pore structure. To enhance the characterization ability of the pore structure, this study introduced fractal theory to investigate the influence of pore structure on hydraulic conductivity. In this study, the pores were conceptualized as a bundle of tortuous capillaries with different radii and the cumulative pore size distribution of the capillaries was considered to satisfy the fractal law. Using the Hagen-Poiseuille equation, a fractal capillary bundle model of hydraulic conductivity for saturated frozen soil was developed. The model validity was evaluated using experimental data and by comparison with previous models. The results showed that the model performed well for frozen soil. The model showed that hydraulic conductivity was related to the maximum pore size, pore size dimension, porosity and tortuosity. Of all these parameters, pore size played a key role in affecting hydraulic conductivity. The pore size dimension was found to decrease linearly with temperature, the maximum pore size decreased with temperature and the tortuosity increased with temperature. The model could be used to predict the hydraulic conductivity of frozen soil, revealing the mechanism of change in hydraulic conductivity with temperature. In addition, the pore size distribution was approximately estimated using the soil freezing curve, making this method could be an alternative to the mercury intrusion test, which has difficult maneuverability and high costs. Darcy’s law is valid in saturated frozen silt, clayed silt and clay, but may not be valid in saturated frozen sand and unsaturated frozen soil.

Study on the Effective Thermal Conductivity of Macro, Mirco and Nano Porous Materials in the Light of the Knudsen Conduction/Radiation Coupling Effect

2010 ◽  
Author(s):  
Ulrich Gross ◽  
Khaled Raed
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Pore Size Distribution ◽  
Porous Materials ◽  
Pore Size ◽  
Effective Thermal Conductivity ◽  
Size Distribution ◽  
Solid Matrix ◽  
Porous System ◽  
Gas Atmosphere

Thermal transport phenomena in porous media are characterized by conduction through solid matrix and filling gas, and also by radiation. The gas is dispersed in the porous system depending on the pore size distribution. In each pore, the gas contributes to the heat transfer between the pore surfaces. This effect is strongly influenced by pore size, gas atmosphere, accommodation coefficient and other factors. A recent publication of the present authors focused on modeling the change of the effective thermal conductivity when the gas atmosphere is changed. In the current contribution, the effect of pore size distribution on heat transfer in macro, micro, and nano insulation materials is presented. Samples were chosen from five different highly porous materials with different pore size distribution within the macro, micro, and nano classes. Porosity and pore size distribution of the samples were chosen to get a clear characterization of the materials. The effective thermal conductivity was measured by applying the radial heat flow method at temperatures up to 1000 °C. Evaluating Knudsen effect from the pore size distribution alone does not give plausible explanation for the measured thermal conductivity. However, it is important to consider the kind of connections between the pores. In case of nano materials, the radiation effect proves to be strongly dependent on the Knudsen number.

Effect of Burning-Out Materials on the Properties of Synthesized Microporous Mullite

2012 ◽  
Vol 151 ◽  
pp. 271-274
Author(s):  
Yu Bao Bi ◽  
Hui Fang Wang ◽  
Wei Lu
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Microporous Structure ◽  
Volume Stability ◽  
Temperature Environment ◽  
High Temperature Environment ◽  
Industrial Alumina

Mullite can be prepared as lightweight refractories for its low thermal conductivity, advanced volume stability at high temperature environment. Using industrial alumina and nature silica powders as starting materials, the mullite aggregates with microporous structure were synthesized by adding some burning-out materials as pore forming agents. The effects of burning-out materials on the pore size distribution, mullite contents and microstructure of microporous mullite have been investigated. The results show that the effects on the mullite contents and microstructure of microporous mullite are significant. All the burning-out materials have a similar effect for the pore size distribution.

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