Analysis of Gas Molecule Mean Free Path and Gaseous Thermal Conductivity in Confined Nanoporous Structures

Abstract

This study comprehensively analyzes the mean free path of gas molecules and gaseous thermal conductivity in confined nanoporous structures through a wide range of temperatures and pressures. A simplified unit cell cubic array structure of nanospheres is used to correlate microstructure features with specific surface area and density of nanoporous materials. Zeng's model is used to describe the mean free path of the gas molecules and the gaseous thermal conductivity in confined nanoporous structures, and experimental gaseous thermal conductivity data from the literature is used to validate the model. The results show that a material's nanoporous structure features are directly related to specific surface area and density. The mean free path of gas molecules in a confined nanoporous structure decreases with increasing specific surface area and density. Thus, nanoporous materials with a relatively high specific surface area and a higher density are more favorable for confining gaseous thermal conductivity in nanopores. This work shows that p = 10 4 Pa and 10 6 Pa are two characteristic pressures at ambient temperatures for the investigated silica aerogel materials. When p < 10 4 Pa, the mean free path of the gas molecules remains constant with varying pressure, while gaseous thermal conductivity approaches zero due to the restrictive effect of the nanoporous structure and the diluted gas molecules. When p > 10 6 Pa, the limiting effect of the nanoporous structure on the movement of gas molecules can be ignored, and so the mean free path of gas molecules in the nanoporous material approaches the mean free path of gas molecules in free space, B Gaosheng Wei 123 Int J Thermophys while the gaseous thermal conductivity approaches the gaseous thermal conductivity in free space. As temperature increases, there exists a maximum value for gaseous thermal conductivity in confined nanoporous materials, but this maximum increases as pressure increases. The maximum gaseous thermal conductivity for the material is also determined in the paper.

Thermal Conductivity of Nano-Crystallized Indium-Gallium-Zinc Oxide Thin Films Determined by Differential Three-Omega Method

“…In our study, the thermal conductivity decreased with an increase in temperature. This temperature dependence is similar to that for crystalline materials because the thermal conductivity of amorphous materials increases with an increase in temperature in the room-temperature region [33][34][35][36]. Furthermore, B. Cui et al were carried out extensive thermal conductivity analysis of IGZO thin films at low temperature and reported that the result of thermal conductivity is varying widely depending on deposition technique such as physical layer deposition, sputtering, and chemical synthesis; deposition power, deposition temperature and structural phases such as amorphous, poly-crystal, and single crystal [37].…”

Suppression of Thermal Quenching for CsPbX3 (X = Cl, Br, and I) Quantum Dots via the Hollow Structure of SrTiO3 and Light-Emitting Diode Applications

“…Moreover, SrTiO 3 , as a porous nanomaterial, can block a small amount of thermal radiation and reduce air convection. The larger specific surface area also increases the collision probability between the gas molecules and the interface, and the heat is dissipated during the transfer process, making the thermal conductivity smaller than that of the bulk material . The lower the thermal conductivity, the worse the heat conduction and the better the heat insulation effect .…”

“…The larger specific surface area also increases the collision probability between the gas molecules and the interface, and the heat is dissipated during the transfer process, making the thermal conductivity smaller than that of the bulk material. 22 The lower the thermal conductivity, the worse the heat conduction and the better the heat insulation effect. 23 In addition, dispersing CsPbBr 3 into SrTiO 3 at the nanoscale can also effectively inhibit the aggregation caused by the increasing temperature, thereby reducing the thermal quenching of CsPbBr 3 PQDs.…”

A critical look into effects of electrode pore morphology in solid oxide fuel cells

“…This result can be explained with the Knudsen number, K n , which is defined as the ratio of the mean free path ( ) of the gas species to the pore diameter of the electrode . For hydrogen, the mean free path ( ) is ∼0.5 μm in the range from 600 to 1300 K . When the pore size is below ∼5 μm, K n is larger than 0.1, and the Knudsen diffusivity contributes dominantly to the total diffusivity .…”